Testing Precious Metals C.m Hoke[1]

TESTING PRECIOUS METALS Gold, Silver, Platinum Metals

Identifying - Buying - Selling A Handbook for the Jeweler, Dentist, Antiquarian, Layman

By G. M. HOKE Author of Refining Precious Metal Wastes

THIRD EDITION

T H E JEWELERS' TECHNICAL ADVICE COMPANY

New York, N. Y.

COPYRIGHT 1946 BY C. M. HOKE

All rights reserved. This book, or parts thereof, may not be reproduced in any form without permission of the publishers.

The First Edition was originally published in The Brass World—Plating—Polishing—Finishing of New York Parts of the Third Edition were published in The Jewelers* Circular-Keystone of New York

PRINTED IN U. S. A.

was founded in 1912, when platinum was first coming into use as a jewelry metal. Its manager, Sam W. Hoke, was a pioneer in the technology of platinum. He patented a series of oxygen-gas torches, used for melting and welding platinum, soldering gold and platinum jewelry, melting quartz glass, etc. In 1912 the melting of platinum was possible in only a few plants in the whole world; today it is a commonplace in even the smaller jewelry factories. C. M. Hoke, the writer of this book, has a background of university training in chemistry and biology, as well as experience in the teaching of chemistry. For years she has devoted her time to instructing jewelers and others in refining, melting, salvaging and finishing the precious metals, and in developing equipment for the control of compressed gases. T H E JEWELERS TECHNICAL ADVICE COMPANY

Foreword The precious metals are always interesting—even the prosaic tasks of testing, refining, working, and selling them command a perennial interest. For many years the writer has been concerned with these matters, and the following pages are designed to answer one group of questions that has arisen time and time again. If you are handling precious metal articles, you will often need to distinguish, for example, between a piece of 18-karat and a piece of 14-karat gold, or to decide whether a given article is white gold or platinum. If you are buying or selling old jewelry or dental golds, you will often wish to know the approximate value of a piece, without taking time for an assay, and possibly without injuring the article itself. The purpose of this book is to describe methods, particularly the touchstone method and its variations, that will give this information. The idea of testing gold with a touchstone is very old. We are told that the Lydians used it in 500 B.C., rubbing the metal against a smooth stone, then comparing the streak with similar streaks made by metals of known composition. When during the Middle Ages men learned to make strong acids, the method became more exact. During the last few years, with the introduction of the many new metals and alloys and combinations that now characterize the precious metal industries, the method has been greatly amplified. In the hands of a careful worker it yields quickly a large amount of useful information. These chapters will first describe the touchstone method as used on the ordinary yellow gold alloys that have been in vogue since the days of our grandfathers. Then we shall cover silver, and the white golds and platinum alloys that came into use at about the time of World War I. Some other methods of identification that do not employ the touchstone will also be described, and full attention will be given to those new alloys and combinations, including the ruthenium alloys, which appeared during World War II.

The book does not discuss assaying (which is the chemical analysis of a small weighed sample) and it gives only a few paragraphs to the problems of the prospector. Its purpose is to assist the jeweler, antiquarian, metal buyer and layman to identify precious metal articles and estimate their value. A knowledge of chemistry is not required. One chapter is devoted to quality stamps and karat marks. Another contains advice not only for the layman with some jewelry to sell, but also for the jeweler or refiner who might buy it. It outlines the evolution of the gold-buying industry, calls attention to the laws under which it operates, and suggests the problems, profits, and responsibilities that accompany it. C. M. HOKE.

Palisade, New Jersey, 1945.

Contents Foreword

7

Chapter I. The Old Touchstone Method and the Yellow Golds

11

Chapter II. Silver and Some Other White Metals

18

Chapter III. The Quality Stamp—"Let the Buyer Beware!"

29

Chapter IV. The Platinum-Group Metals and the White Golds A. New Metals; Old Tests B. New Metals; New Tests C. Some Other Tests

39

Chapter V. Buying and Selling Old Precious Metals

63

Chapter VI. Some Paragraphs for the Prospector

78

Appendix

83

A. B. C. D.

A List of Equipment. When Handling Strong Acids. How to Determine Specific Gravity. A Table of Metals, their Melting Points and Specific Gravities, and their Responses to Acids and to the Oxy-Gas Flame. E. Some Definitions and Formulas.

Index

91

CHAPTER I

The Old Touchstone Method and the Yellow Golds HE equipment for testing ordinary golds is shown in the frontispiece, though most workers will add one or two more acid bottles. There is the smooth, flat stone, of slate or fine-grained basalt; there are the so-called needles—pointed bits of yellow gold of various finenesses, each marked with its quality; a small triangular file; and the acid bottles. The gold buyer will need in addition a scale and a set of weights. Our first task is to make sure that the article to be tested really is gold. We then determine its quality by rubbing it upon the stone so as to make a mark or streak, and comparing this streak with streaks made by the standard needles. This in one paragraph is the whole story of the touchstone tests. Let us first acquaint ourselves with the ordinary, old-fashioned gold alloys of a golden color, postponing our examination of white golds, silver and the platinum metals until later. For your first step, obtain several articles of different types, but of whose quality you are sure; for example, a genuine gold coin or a piece or two of high-grade jewelry made and stamped by a reputable manufacturer; some moderately-priced articles; a handful of very cheap novelty jewelry that is finished to look like gold; and finally, for comparison, a piece of clean brass. The more articles, and the larger their variety, the more quickly you will learn to identify and appraise the "unknown" articles that will come to you.

T

THE FILE

The experienced gold-buyer always begins by filing a deep notch in the article, in order to penetrate any outer layers, and he may learn immediately that the gold is only skin deep. Mediumpriced jewelry—rolled-gold or gold-filled goods—consists of a core of inexpensive metal to which an outer layer of karat gold has

been affixed. The core is usually brass; occasionally it is a gold alloy of lower karat; and during World War II use was made of a sterling silver core, instead of brass, because wartime regulations forbade the use of brass for jewelry manufacture. Low-priced novelties are apt to be electroplated and their surface film of precious metal is very thin indeed. Most high-grade articles are flash-finished with a light electrodeposit of pure gold, and when new may be further protected by lacquer. While these latter films can be removed by a few strokes of the file, the heavier coatings, such as those found in gold-filled or rolled-gold goods, are pierced only by a deeply-filed notch. Accordingly, as we said, the experienced buyer always begins by filing a deep notch. NITRIC ACID

The first acid bottle contains chemically pure (C.P.) nitric acid, full strength, which can be bought from a drugstore or supply house. This acid attacks the majority of metals, and will destroy skin, clothing, woodwork, and so on, and therefore must be handled with care. If you should get acid on your skin or clothing, immediately wash it off with much water—hold your hand under the faucet and let the water run on it freely—and very little harm will be done. If no running water is nearby, provide a basin of water for immediate use if needed. Note that the glass stopper of the acid bottle is extended into a long tongue. With this tongue, apply a small drop of nitric acid to each of your metal articles, on a clean surface or in a freshly-cut notch, and watch the results, noting the color changes, if any. After a half minute, rinse the acid off with plenty of water, dry, and see if the metal has been attacked. Brass or copper boils up instantly and the acid turns green. Gold of 6-karat# or lower will be attacked almost as promptly, and will show a green color, due to the copper with which it is alloyed; 10-k will darken; ordinary gold of 12-k or better will show little or no reaction. * The term karat means a twenty-fourth part, and expresses the proportion of gold in an alloy. Thus pure gold is 24-k; 6-k gold is 6/24ths (or i/4) gold, the remaining i8/24ths being some other metal or metals. Pure gold is also described as "fine" gold, or as being "1000 fine," and 6-k gold is sometimes spoken of as "250 fine."

In general, any metal of the yellow color of gold that will stand this nitric acid test, may be assumed to be gold or a gold alloy. Note that we say of yellow color, for there are several white metals, such as platinum and stainless steel, that resist nitric acid. If possible, get a friend to hand you some unstamped articles of whose quality he is sure; examine these "unknowns" and report to him regarding their character, repeating the tests until you have learned how the various metals and alloys respond to the acid test. DETERMINING THE KARAT

When the acid test has convinced you that an unknown is indeed a gold alloy, your next step is to determine its karat, using the standard needles and the touchstone. Rub first one needle and then another upon the stone, thus making a series of streaks upon the smooth surface. Each streak is a thin layer of metallic molecules—molecules of gold and molecules of base metals. Now with the stopper of your acid bottle, draw a little nitric acid across each streak. As you would expect, the base metal molecules, thus exposed to the acid, will dissolve promptly, while gold molecules remain unchanged; hence, streaks made by the lower karat needles will almost disappear, but those of higher quality will show little or no response. Returning then to your unknown, rub it hard against the stone, making a streak. Suppose you suspect that it is about 10-k quality, maybe less. Beside the first streak make two others, one with the 10-k needle, another with the 8-k needle. With the stopper of your acid bottle, draw nitric acid across the three streaks of metal.

Watch the way in which the acid works. As soon as you find a standard streak whose response is the same as that of your unknown, then you have found the approximate fineness of the unknown. By "response" we mean the speed and completeness with which the streak is attacked. But suppose your unknown is of such high quality that it is not affected by plain nitric acid. We must now turn to the second bottle, which contains chemically pure hydrochloric acid, and we shall make up some aqua regia. AQUA REGIA

Aqua regia is a mixture of nitric acid and hydrochloric acid. The name means royal water, and was used by the ancients because the mixture dissolves gold, the noble metal. Practically the same results are obtained by adding a little table salt to diluted nitric acid. When aqua regia is first made up, chlorine is evolved, a noxious gas which attacks metals and should not be permitted to reach machinery, balances, and so on. Nor should the mixture be kept in a stoppered bottle, for the evolving gas might break the container. Because of this (and also because it spoils on standing) aqua regia should be made up only as needed. Mix it the same way every time; the exact proportions are not important, but get accustomed to a certain mixture and continue to use it. It is possible to mix the two acids right on the stone, after making the streaks; that is, draw a little nitric acid across the streaks, then add a little hydrochloric acid, letting the two acids run together. This is not good practice, however, because each stopper becomes contaminated with the other acid, creating confusion. A better plan is this: With a medicine dropper measure out ten drops of nitric acid into a tiny bottle; add ten drops of water, preferably distilled; then using a clean dropper add two drops of hydrochloric acid. This gives you enough aqua regia for about a dozen tests. Wash your medicine droppers after every usage. Returning then to the streak that was not affected by plain nitric acid, wash and dry the stone, and apply aqua regia with a small glass rod or a clean medicine dropper. Even fine gold is attacked by aqua regia. By comparing the response with first one standard

needle, then another, you can determine the quality of your unknown. This test differs slightly in principle from the nitric acid test, in that aqua regia dissolves the gold molecules as well as those of most base metals. Some workers make up their aqua regia with even more water than above, because the reactions proceed more slowly with the dilute mixture and therefore are easier to compare. Some workers use a different proportion of hydrochloric acid. Note the color changes. Fine gold when dissolved gives a yellow color, but this is usually masked by the green color of the copper that is almost always present in gold alloys. Nickel, used in most white golds, also gives a green color. Silver when treated with aqua regia, forms a cheesy white substance on the stone which may well confuse a beginner. Because of the influence of the alloying elements, it is well, if possible, to use yellow gold standard needles when testing yellow gold unknowns, green gold needles with green gold unknowns, and so on. GREEN GOLDS

Green gold alloys, especially those of high quality, contain considerable silver and little or no copper. The response of silver to aqua regia is peculiar, as we shall find in a subsequent chapter. Green golds respond more slowly to aqua regia than yellow golds of the same karat, and may lead you to think that they are more

Standard needles for testing the quality of white golds and green golds.

valuable than they are. Therefore, we repeat, when testing green golds, use standard needles made with green gold points. RED GOLDS

These alloys contain more copper and less silver than the yellow golds of the same karat, and respond slightly more rapidly to aqua regia. WHITE GOLDS

A white gold is an alloy that contains enough of some white metal to destroy the yellow color. There are two whiteners in general use—nickel and palladium. Most inexpensive white golds consist primarily of gold and nickel, to which copper and zinc may be added, sometimes other metals. When testing them, use the same procedure as with yellow golds, but it is wise to use standard needles made with points of white gold. Many better quality white golds consist of the same elements, gold, nickel, and small amounts of other base metals. However, many white golds of especially fine quality, including many dental alloys, are whitened with palladium. Now there is considerable difference in the value of gold-nickel and gold-palladium alloys, assuming that the proportion of gold is the same. Hence your concern, after deciding that a given article is white gold, is to learn what kind of white gold it is—nickelgold or palladium-gold. This takes us to a later chapter of this story, in which we cover palladium and nickel. DENTAL ALLOYS

There are dozens of dental alloys in use, ranging in value from iridio-platinum pins, through the wrought and casting golds and high-karat solders, down to the amalgams, base metal "technic" alloys, and occasional pieces of stainless steel and aluminum that may find employment in dental work. Some dental fillings are almost pure gold. If a piece of yellow metal has been in use in the mouth for some time and still presents a tarnish-free surface, it probably is gold of good quality, and should respond to the acid and touchstone tests in much the same manner as the jewelry alloys. Do not be deceived by the word

solder as used in dentistry; it may refer to a gold alloy of high value, used to join together the parts of a denture. The tendency today is away from the conspicuous yellow golds and toward the white alloys—white golds and alloys containing platinum-group metals—which will be discussed fully in a later chapter. Dental golds do not carry the quality stamps that are commonly found on jewelry, hence gold buyers who distrust their own ability to appraise metals often refuse to quote on dental alloys. For that reason the buyer who can appraise properly, will find excellent opportunities in this field.

Clean the stone frequently to remove all marks, perhaps by rubbing it with fine pumice, or by covering the spots with a little aqua regia. Wash it free of acids before putting it away, or the traces of today's tests may confuse you tomorrow.

A list of the equipment used in these tests will be found in the Appendix. The Appendix also contains a table of metals with their melting points and specific gravities, as well as their responses to nitric acid, to hydrochloric acid, and to the oxy-gas flame.

CHAPTER II

Silver and Some Other White Metals T ^ H I S is the group that offers the greatest challenge to the preJ- cious metal buyer, and can offer him the greatest profit. It includes on one hand the silver alloys, the white golds and the platinum metals, and on the other hand a vast array of alloys like stainless steel, which, though handsome and useful, are not precious metals. The purchaser wants to be able to separate out, from a trayful of white metal articles, precisely those that are valuable to him, and to do it with speed and assurance. These chapters will present him with tests that should give him this assurance. There are about seventy metals known to science (the number is uncertain because some are on the borderline between metal and non-metal), and of this number all except gold and copper are described as white. When the student contemplates all the possibilities of composition and value that are presented by the words "a white metal" he must realize that the task calls for care, knowledge, and patience. Fortunately for our purpose, most of the seventy-odd white metals are quite unsuited to jewelry making. Thus mercury is liquid at ordinary temperatures; tin is much too soft; potassium reacts violently with plain cold water; radium gives off rays that destroy the flesh; and so on. Our attention therefore will be placed primarily upon those white metals that are precious, and upon those that are associated with them, or are apt to be confused with them. THE MAGNET AS A DETECTIVE

Gold buyers often use a magnet to locate such things as steel springs in bracelets. If a piece of metal is strongly attracted to a magnet it is probably iron or steel. However, certain nickel and cobalt alloys and some kinds of white gold also respond to the magnet, which therefore should not be relied upon too implicitly, es-

pecially as some of the stainless steels are attracted only feebly or not at all. Other metals besides iron respond to the magnet; some stainless steels do not.

T H E FLAME TEST

If you can turn the flame of an air-gas or oxygen-gas blowpipe on a piece of suspected metal, you can, within a few seconds, obtain an excellent idea of its nature. Nickel, chromium, brass, and most other base metals promptly turn black. Most base metals will melt, forming oxides of characteristic color and form. White gold alloys will melt promptly in the oxy-gas flame; more slowly in air-gas. Or, if the flame is removed before actual melting occurs, a definite darkening is visible. This is also true of sterling silver. Fine silver when molten absorbs oxygen, and on cooling expells it with violent spitting and "crabbing". This tendency is less conspicuous with sterling and coin silver. Stainless steel soon shows a darkening; if heated further it will ignite and burn with a hissing and sparkling flame; the final result will be a shapeless lump of black oxides. Tungsten, tantalum, and molybdenum change color at low temperatures, and soon begin to burn in the oxy-gas flame, though they will not become actually molten. The response of platinum and its high grade alloys to a flame is highly characteristic. (By high grade alloys we mean iridioplatinum, or others in which only precious metals are present.) Suppose you bring the metal to a brilliant red heat, then remove the flame. There will be no darkening whatever. Heat it still further using an oxy-gas flame, and melt it; it melts smoothly and cleanly, without forming any oxide or crust. When the button cools, it will be white and smooth. Base metals, treated in that way, become a mass of clinkered oxides. Palladium and alloys rich in palladium show colored oxides at about 4000 C, but when heated further these disappear, and if the metal is cooled quickly they will not have time to form again and the cooled button will be free from tarnish.

Molten palladium absorbs very large volumes of gases, and if the flame is removed suddenly the gases are expelled violently. The button that remains will be distorted and honeycombed with bubbles. Low grade platinum alloys when heated strongly will darken, in proportion to the base metal present. Fine gold, heated to redness, will cool without changing color. But if even small amounts of base metal are present, the surface after cooling will show a film of oxide. The oxy-gas flame, if properly handled, is thus one of the most illuminating of all quick tests, and the air-gas flame is almost as useful. This test will be discussed again in Chapter IV, and a chart showing the responses of several metals to the oxygen flame is given in the Appendix. SPECIFIC GRAVITY

In general the precious metals are heavier than base metals, and the experienced worker can obtain a hint as to the value of an article merely by "hefting" it in his hand. This ratio between the bulk and the weight of a substance, called its density or specific gravity, is often helpful in identification. The student soon observes that platinum and its high grade alloys are somewhat heavier than the white golds; while steel, nickel, silver, and most of the base metals are so much lighter than platinum that there is small excuse for a mistake. Tungsten and tantalum are two base metals of very high specific gravity, comparable with that of platinum. However their leaden color, and the fact that they ignite under the oxy-gas flame and form colored oxides, reduce the chances of confusion. This method of identification, which has both its advantages and its limitations, will be discussed again in Section C of Chapter IV, and in the Appendix. How SILVER REACTS

As in Chapter I, the first step is to provide yourself with several articles of whose composition you are sure, then apply to them the various tests, in turn, and observe the results. Obtain a piece of good quality sterling silver, something made recently and stamped

by a reputable manufacturer; a silver coin; perhaps a bit of some lower-grade silver alloy; and some stuff that you know to be silverplated. First remove any surface coat, such as lacquer, and to each article apply a drop of nitric acid. Let it remain for thirty seconds or so, then rinse it off and see if the surface of the metal were attacked. You will find that nitric acid reacts with silver, even the highest grade, turning dark and making a gray spot on the metal. Fine silver, when dissolved in nitric acid, gives a colorless solution that darkens after exposure to light. Sterling silver and coin silver show some green color, the green being due to the copper with which they are alloyed.

To confirm silver, place a fresh drop of nitric acid on a clean surface, let it react for a half minute, then with the point of a penknife drop in a single small grain of table salt. A white substance will appear—silver chloride—of a cheesy consistency. This is characteristic of silver. Instead of the grain of salt you could use a tiny drop of dilute hydrochloric acid. In effect this is almost the same as applying a drop of aqua regia. We think of aqua regia as a powerful solvent since it will dissolve gold. However, it is surprisingly slow to attack silver. Make the test and see; note that the nitric acid in it will eat into the surface a little, but very soon the white cheesy stuff forms, and protects the metal from further attack. Wash the metal and you will find that a whitish spot remains, difficult to remove. This will help to explain why green gold, which contains much silver, responds more slowly to aqua regia than does yellow gold

of the same karat. Some of the high-karat green golds are almost insoluble, even in hot aqua regia. Here is another way to establish silver: In another bottle mix up nitric acid and a few crystals of potassium dichromate. Place a drop of this solution on the suspected article (after getting rid of lacquer, etc.) and note the color effect. Silver will show a very strong, definite red, through the formation of silver dichromate. SlLVERPLATED GOODS

The recognition of silverplated ware is usually easy. File a deep notch and apply nitric acid to the cut, and note the difference in appearance and behavior of the silver surface and the base-metal tains no silver at all. Sometimes a brass core is found. Both of these core materials react quickly to nitric acid, causing it to bubble and turn a deep green. core. The favorite core material is a copper-nickel-zinc alloy which is called "nickel silver" or "German silver/' but which conOrdinary silverplated ware is of such small value that refiners and gold buyers normally refuse to buy it, so it is important to be able to recognize it every time. GOLD-ON-STERLING

In Chapter I we mentioned "gold" jewelry which was found to consist of a sterling silver core to which a thin surface layer of gold has been applied. The wearer may think of such jewelry as gold, but to the buyer it is silver. At present silver prices it is not to

Thin sheets of karat gold are welded to one or more surfaces of a thick billet of less expensive metal—usually brass or a nickel alloy, sometimes sterling silver—and the whole is then rolled very thin. The resulting thin sheet is used in making gold filled or rolled gold plate jewelry. In order to meet U. S. standards the gold layer must be of at least 10-k quality. If the weight of the karat gold is more than 1/20 of the total weight, the jewelry may be stamped "gold filled" The term "rolled gold plate" is used when the gold layer is thinner.

be ignored, and sometimes there is enough gold present to add a little to the buyer's price. This combination is normally recognized in the preliminary tests involving nitric acid and a deeply-filed notch. Fresh, wellmade goods present a handsome gold-like appearance, but if the gold film is thin, the silver soon tarnishes underneath the gold. This combination attained special vogue during World War II at the time when silver and fine gold were available, while copper and nickel—the metals so generally used in the cores of inexpensive jewelry—were subject to wartime restrictions. The fact that silver responds only feebly to aqua regia has led some careless buyers to misjudge the value of this combination, to their loss. Fortunately for them, it is apt to be clearly stamped "Sterling." Sometimes the outer layer of gold is of sufficient thickness and quality to class the goods as "rolled gold" or "gold filled"; but these goods are generally stamped with a quality mark; e.g., "Rolled Gold Plate on Sterling" or "Sterling -f- 1/20— 12K." T H E VARIOUS SILVER ALLOYS

Pure unalloyed silver, called "fine silver," is so soft that it has few practical applications. The most important alloy is sterling silver, which contains 925/ioooths fine silver, the remainder usually being copper. The word "sterling" goes back to the twelfth century; it seems that five towns in eastern Germany were banded together in the so-called Hanseatic League; they were free cities and maintained their own currency. The British soon learned that their coins, called the coins of the Easterlings, were dependable; hence the term "sterling" as a stamp of quality. Coins of the United States of America are 900/ioooths silver, the remainder being copper. Much jewelry and tableware used to be made of this alloy, and may be stamped "Coin" or "Coin silver." Alloys of lower silver content are often encountered, not only in the coinage of several foreign countries, but also in articles of commerce, but the designation "silver" cannot now be used legally in connection with them in the United States. Imported goods may be encountered, stamped "Silver," which on assay may prove to be of very poor quality indeed. It is sometimes desirable to make simple tests to distinguish be-

tween sterling, coin and lower grade silver alloys, but most observers have found that it cannot be done with the same assurance and satisfaction as with the gold alloys. Sterling silver and coin silver differ by only 25 parts per 1000, or 2]/2 percent, and when we recall that both the silver and the copper are soluble in nitric acid, we can see why the acid test has its limitations. However, by having both surfaces clean and smooth, and by applying equal amounts of acid to both surfaces and exposing both together to the light for the same length of time, and noting the color changes, the difference is detectable. Silver of lower grade, if alloyed with copper, can easily be distinguished from sterling silver in the same way. Unfortunately, these lower grade silvers may contain a variety of alloying elements —more or less nickel, or zinc, or cadmium—to fit them for different purposes, and unless you have some knowledge of the alloying elements, these simple spot tests can be misleading, and experienced workers advise against their use. SILVER SOLDERS

Silver solders, also called silver brazing alloys, are of many formulas, containing from five percent to about eighty percent silver, the balance being copper and zinc and perhaps some cadmium. Large amounts of these alloys have been consumed in recent years, in dozens of applications, not only in the manufacture of jewelry, but also in such jobs as the assembling of incendiary bombs, the repair of ice-cream freezers, the construction of equipment for the chemical industries, and many others. While not of high intrinsic value, these silver brazing alloys should not be ignored by the metal buyer, especially as they may often be found in large quantities. SOME WHITE BASE METALS

Many base metals are attacked and dissolved by nitric acid, but by no means all. Obtain scraps of various metals, such as lead, tin, pewter, Britannia metal, tungsten, stainless steel, aluminum, chromium-plated and nickel-plated ware, and so on. Clean them well to remove any surface grease or lacquer, then touch each with a drop of nitric acid. Let it act for a half-minute or so, while you

observe any color changes, then wash well and notice if the surface were etched or spotted. To describe all the effects fully would take more space than is here available; moreover, a few minutes spent at such tests will teach you more than hundreds of words. So we repeat: practice with pieces of metal of whose nature you are sure, exposing them to various tests and comparing results. For instance, we suggest that you try the dichromate mixture mentioned above, on other white metals beside silver. Lead shows a yellow color; Britannia metal turns dark. Platinum is not affected in the least, nor is high-grade white gold, but palladium will be darkened and will show a spot. NICKEL-SILVER

The terms "nickel-silver" and "German silver" are applied to an important series of white alloys in which copper, nickel and zinc are the principal components. Both terms are highly misleading, since no silver at all is present, and many other names have been suggested, including "nickel-brass" and synthetic words like "Cunizin" and "Nicuzin," none of which have received general favor. Tableware and hollow-ware made of nickel-silver and electroplated with silver, nickel, or chromium, have been made in enormous quantities. Rolled and filled gold jewelry, especially that whose outer layer is white gold, is generally made on a nickel-silver base; and there are dozens of other applications. Accordingly it is important that the gold buyer be able to recognize these nickel-silver alloys wherever found. They are attacked vigorously by nitric acid, showing a strong green color because of the copper and nickel content. When heated strongly they darken; under the oxygen flame they ignite and burn to a black clinker, meanwhile conferring a green color to the flame. STAINLESS STEEL

This handsome but inexpensive alloy, stainless steel, has had quite a vogue for sports jewelry, men's belt buckles, wrist watches, etc. In appearance it resembles white gold or platinum. Oddly enough it is not readily attacked by nitric acid nor by aqua regia,

and for that reason it has occasionally deceived unwary appraisers. As we have indicated, some kinds are attracted to the magnet, some are not. It is considerably lighter in weight than either white gold or platinum, and most jewelers will at once notice this lack of "heft". As we mentioned above, it darkens under the oxy-gas flame, then ignites and burns to a dark clinker. But if you are in doubt about any article of white color and noticeable hardness, which resists the action of nitric acid and of aqua regia, pause a moment and then test it with plain hydrochloric acid. If possible, heat either the article or the acid somewhat; hydrochloric acid attacks the stainless steels promptly, making a definite spot or dissolving the streak in a short time. Sulphuric acid also attacks stainless steel; so does a solution of ferric chloride. None of these affects white gold or platinum. RESISTANCE ALLOYS

There are dozens of more-or-less white alloys on the market, which though not stainless steels by definition (since they contain little or no iron) are often confused with them. We refer to those heat- and corrosion-resisting alloys of which Stellite, Nichrome and Illium are only three examples of a long list. Chromium, cobalt, nickel, tungsten, silicon, manganese and other elements may be present, and the number of formulas is legion. Occasionally such alloys present an appearance that might confuse the metal buyer, and many of them resist nitric acid surprisingly well. But mostly they are lighter in weight than platinum or white gold, and their crystalline structure and their "feel" under the file give sufficient warning. Their melting points are high, but under the strong heat of the oxy-gas flame they will ignite and burn, after the manner of other base metals. SOME LESS COMMON METALS

Tungsten, tantalum and molybdenum are three of the semi-rare metals that have found growing commercial importance during

recent years. In color they are somewhat dark, and are tough, heavy, strong and hard. Their carbides are extremely hard, and are compacted and sintered into points or blades for drills, cutting tools and the like, for which purpose they rival the diamond. These metals all possess remarkable resistance to nitric acid, aqua regia, and most other reagents, and accordingly have some times been confused with the platinum metals. But above red heat they all oxidize readily, and under the oxy-gas flame they ignite and burn to form colored oxides. CONTACT POINTS

Electrical contact points must have high heat and electrical conductivity, hardness, strength, and resistance to corrosion at the high temperatures of the electric arc. Many metals and alloys are being used in their manufacture—silver, copper, platinumgroup metals, tungsten, tungsten carbide, cobalt, and others. Sometimes a point consists of two alloys welded together, the combination then being brazed or welded to the device of which it is a part, and many of the alloys involved are quite complex. Old contact points can be quite a problem to the metal buyer. Knowing that much platinum and iridium go into this market, he is tempted to buy the things, even after experience has taught him that he is more apt to lose than to profit when handling them. The task of appraising them and recovering the precious metals, if any, is difficult, and many professional refiners refuse to buy them. Accordingly the beginner is advised to approach this market with caution. CHROMIUM PLATE

Chromium is a hard white metal, unusually resistant to most corrosive agents. Chromium plate, when properly applied, is a handsome finish and sometimes is used on cheap white gold jewelry, as well as on many base metal articles. It resists nitric acid, and therefore is sometimes mistaken for white gold or platinum. However, it is attacked readily by hydrochloric acid, and by sulphuric acid. When heated under the airgas or oxy-gas flame, it blackens promptly.

RHODIUM PLATE

Rhodium plate is also deceptive. Rhodium is a metal closely related to platinum, costing more per ounce than platinum itself. It can be deposited electrolytically in a very thin layer, on silver or base-metal articles, to give them a handsome appearance, free from tarnish. Rhodium is not attacked by nitric acid, aqua regia, nor any other single acid. It is fairly hard to the file—almost as hard as chromium plate. But the deposit is always so thin that a few strokes of the file will expose the metal below. For that reason it should not cause any great confusion to the buyer of precious metals. WHITE GOLDS

The tests described so far, when applied to most white golds, will be suggestive, but not always conclusive. You may still be uncertain as to whether the unknown is white gold or a platinum metal alloy of some kind. We shall therefore return to the white golds in a later chapter, with conclusive tests. THE PLATINUM METALS

These metals and their alloys are so important, not only in jewelry and dentistry but in many other applications, that an entire chapter will be given over to them. For the moment we shall content ourselves with remembering the facts we have recently noted: that platinum is not attacked by nitric acid nor by hydrochloric acid; that its melting point is very high; that it melts cleanly under the oxy-gas flame and cools again without the formation of visible oxide; and that it is noticeably heavier than most other white metals. Palladium is the one metal of the platinum group that is attacked by nitric acid. It dissolves promptly to give a deep brown solution. It is much lighter in weight than platinum. Palladium electroplate is sometimes used to give a handsome non-tarnishing finish to jewelry or scientific instruments. Alloys in which gold and palladium are the main constituents are important in dentistry, also they form one kind of white gold. All of these, and others, will be discussed more fully in Chapter IV.

CHAPTER III

The Quality Stamp—"Let the Buyer Beware!" Since gold and silver have been used in coinage for many centuries, it is natural that their stamping or marking should be regulated by law. Such laws are not only a protection to the purchaser, but are of equal value to the manufacturers because they sustain public confidence in the industry. Regulations for the platinum metals are of more recent date. Everyone who handles precious metal articles should understand these laws thoroughly. Thus the manufacturer must keep his alloys high enough to meet the law, but not so unduly high as to jeopardize his profits. The retail jeweler, who is equally liable before the law, does well to check the goods he sells and to give attention to the reputation of the manufacturers from whom he buys. The metal buyer, in his turn, has good reasons for observing and interpreting the various stamps. For example, if an article is marked "10-k," he need not waste time testing it against the 12-k needle. Also, he should familiarize himself with the trademarks of the various manufacturers, and observe which, if any, are associated with sub-standard goods. Finally, all groups must understand the meaning of "tolerance" in marking, which will be explained shortly. BRITISH HALL MARKS

The marking of gold jewelry began in England in the fourteenth century. The Goldsmiths' Company, incorporated in 1327, and certain other Guilds, found it necessary to organize for the protection of their craft and of the public against fraud. They had, among other functions, that of testing gold and silver articles at their several Halls. A small sample was cut from each piece and assayed, and the article then received four or more stamps, including the quality mark, a town mark, a date letter (changed each year) and a maker's mark. Various symbols were used, such

as a leopard's head, a crown, a lion, and the like. Goods made between 1784 and 1890 also carried a duty mark indicating that a certain tax had been paid. Stamping was not compulsory, and small articles were not always marked. It should be noted that 13 CARAT GOLD.

9 CARAT GOLD.

STANDARD SILVER.

Some British Hall marks. These were used by the Birmingham Assay Office.

these marks were impressed not by the maker, as in the United States of America, but by the Guild Halls, after assay. Hall marking has been the subject of a considerable literature, which is well worth the study of the antiquarian and historian. AMERICAN LAWS AND STANDARDS

In this country the manufacturer himself, subject to law, is permitted to affix quality marks and trademarks to his goods. The United States National Stamping Law, covering falsely or spuriously stamped articles made of gold or silver or their alloys, was enacted June 13, 1906. The text may be found in almost any law library or big public library. (Ask for Rev. Stat. U. S., vol. 34, pt. 1, p. 260, 59th Cong., 1st Sess., Public Law 226.) Handy and Harman, silver dealers at 82 Fulton Street, New York, sell a reference book called Handy Book for Manufacturers, which contains, among other useful facts, the full text of the law just mentioned, as well as summaries of the laws affecting plati-

num, of the several Commercial Standards which now have the effect of law, and of the Canadian law applying to the marking of precious metals. Another most useful volume is Trademarks of Jewelry and Kindred Trades, published by the Jewelers' Circular-

Some American stamps. They consist of the quality stamp and the maker's registered trademark.

Keystone, 100 East 42nd Street, New York. This book illustrates several hundred trademarks, and in addition summarizes the stamping laws and explains their application. The manner in which the various silver alloys may be stamped has already been discussed in this book—see Chapter II. "TOLERANCE"

Our lawmakers have assumed that jewelers and silversmiths are subject to human error, so they allow a "tolerance" between the quality indicated by the stamp and the actual quality as determined by an assay. The law also allows for solder, and requires that the article, solder and all, must approach within a certain percentage of the stamp. Thus the law of June 13, 1906, as summarized in the Handy Book, provides that: "If an article is made of gold and is stamped gold, it must also bear a quality mark such as *io karat' (10-K), '14 karat' (14-K). "If an article of gold is given a quality mark, the fineness by assay must not be lower than:—

Watch Cases and Flatware Other articles, not including solder

.003 less than stamped quality. 0208 (i/2 karat) less than the stamped quality. "However, the assay of a complete article, including solder, must not be more than .0417 (1 karat) under the stamped fineness per karat. "For example, the gold in a 14-karat watch case, free from solder, must be at least .5803 by assay. The entire case, including solder, must assay at least .547 (13 karat). A gold ring, not soldered, stamped '14-K' must assay at least .5625 (13I/2 karat). The gold in a brooch stamped '10-K' must assay at least .3958 (gi/2 karat) and the entire brooch, solder and all, must assay at least .3750 (9 karat). "The silver in any article stamped 'Sterling Silver' should assay .925, and the silver in an article marked 'Coin Silver' should assay .900. The silver in an article, not including solder, must not be less than this by more than .004. For example, an article marked 'Sterling Silver,' free from solder, must assay at least .921. "Soldered parts must not reduce the assay of the entire article, including solder, by more than .010 under the standard assays of .925 and .900, respectively, for sterling silver and coin silver. For example, an article marked sterling silver when melted, including solder, must assay at least

Most manufacturers make their goods as close to the limit of tolerance as they dare. Many of them, either wittingly or unwittingly, go below this tolerance. The buyer must keep this possibility in mind when he is calculating the value of a precious metal article. LAWS FOR STAMPING PLATINUM

For some years after the introduction of platinum as a jewelry metal there was confusion regarding its marking, and much misbranding, adulteration and fraud took place. Three of the States in which considerable platinum jewelry was manufactured—New Jersey, New York, and Illinois—passed laws regulating the stamping of platinum and its alloys. And finally, on June 20, 1938, the National Bureau of Standards made effective a series of regulations, based on these State laws, that cover the entire nation. The full text of the New York State law will be found in the Handy Book. Copies of the new National Standard, known as Commercial Standard 66-38, may be obtained from the Superintendent of Documents, Washington, D. C, for 5c. Briefly its main provisions are as follows:

Articles may be stamped "platinum" or "plat," provided all parts of the article purported to be of platinum shall constitue at least 985/1000 parts platinum. If platinum assaying 985/1000 parts pure has been combined with gold the article must be stamped with the karat mark indicating the fineness of the gold in conjunction with the word or abbreviation of platinum, as "14K & Plat." When platinum is alloyed with iridium, palladium, ruthenium or osminum, these articles must be marked in fractions designating the content of these metals. Merchandise bearing quality marks must also be stamped with a registered trade mark.

Since the rules regarding the stamping of platinum alloys are new, a great deal of platinum jewelry now in use was made before these controls were drafted. Accordingly some of the marks on platinum jewelry are misleading now. For years palladium was more expensive than platinum; therefore it was accepted practice to use palladium with platinum, without mentioning the fact. Later the price of palladium fell below that of platinum, and a metal that had once enhanced the value of an article became a cheapener. This situation is only one of the reasons why the purchaser should test platinum articles with extra care. OTHER COMMERCIAL STANDARDS

The National Bureau of Standards, in co-operation with the precious metal industries, has formulated several other "Commercial Standards" that may be of interest. These Standards have their origin in the Bureau, rather than in the legislative halls, and are a crystallization of trade practices. They are subject to amendment when an interested industry feels that changes are advisable, and they are enforced by the Federal Trade Commission. Copies may be obtained from the Superintendent of Documents, Government Printing Office, Washington, D. C, at five cents each. Other standards may possibly be adopted in the future. The following are now effective: Marking articles made of silver in combination with gold—Commercial Standard 51-35. Marking articles made of karat gold—CS 67-38. Marking of gold filled and rolled gold plate articles other than watchcases—CS 47-34, with amendments of February 25, 1939. Bui-

letin TS-1942, of July, 1933, defines the terms "Gold filled" and "Rolled gold plate." Marking of jewelry and novelties of silver—CS 118-44. ENFORCEMENT

While the marking of precious metals has, as we see, been subject to law for centuries, obedience to these laws is not yet perfect. But the fight for honesty in marking and in advertising is being carried on actively by a number of organizations, some of them maintained directly by the precious metal industries. The reader who finds instances of fraud or misrepresentation would report them at once to the Better Business Bureau of his city; or, he or his jeweler should communicate with the Jewelers Vigilance Committee, Inc., New York 19, N. Y. These groups, in co-operation with the Federal Trade Commission and the National Bureau of Standards, have accomplished much, not only in the enforcement of penal laws, but also in obtaining official condemnation of various borderline cases. Also the American Gem Society of Los Angeles, through its members, has done a great deal toward clarifying the advertising and labeling of diamonds and other gem stones. STANDARDS IN FOREIGN COUNTRIES

Each nation has its own standards, not only for the alloys used in coinage, but also for silverware and jewelry. In Chapter II we observed that the word "silver" on a piece of jewelry does not mean the same thing in all lands. To give the details of all these varying standards would not be profitable here, inasmuch as the buyer rarely is sure of the origin of the old metal he buys. The wise practice is to confirm all stamps by one or another of the methods described in these chapters. "LET THE BUYER BEWARE!"

If every article made of precious metal was truthfully stamped, there would be little need for a book like this. But many articles are never marked at all—dentures and chemical ware, for example. And the antiquarian handles articles made before the present laws were framed. An article can be truthfully marked when made,

then, perhaps because its thin outer layer is worn off, or because some repair job added considerable solder or even an additional part of a different composition, the old mark may have become misleading. Finally there is always the possibility of fraud. Thus it is clear that the buyer of old precious metals must indeed be wary. One well-known buyer says, "Never believe a karat mark unless it is accompanied by a reputable trademark, and sometimes not even then." If there is no trademark, the stamp may well be quite meaningless. Chains and mesh are probably the worst offenders. It is recognized that considerable solder is needed in making some kinds of chains, and the wise buyer will assume that even more than that is present. Links that test say 12-k on the stone, when melted down and assayed may turn out to be 10-k or less; chains that test 10-k on the stone may assay 8-k. And so on. SOME PRECAUTIONS

If an article consists of more than one part, like the old-fashioned watchcase with front, back, bezel and bow, test each piece separately, as those less exposed may be of lower value. Lockets and big cuff links sometimes are re-inforced by a base-metal disk inside. Examine the pin and safety catch on brooches. Do not hesitate to file deep notches, maybe two or three, on different surfaces of each piece. Remember that an old article may have been repaired, with the addition of much solder or even a new low-karat segment. Articles such as candlesticks are often made of a hollow metal shell which is filled or loaded, sometimes with pitch, sometimes

with lead which has been melted and poured in. Sometimes the base alone is loaded. This same scheme has been used with heavy link bracelets, etc., and has occasionally deceived the inexperienced observer. Rolled or filled gold requires special care. It consists largely of base metal such as brass, with a thin layer of karat gold on the outside. Usually this outer layer is 10-k or 12-k. You may find a stamp reading "1/10 12-k." Analyze this stamp and you will realize that this article when new assayed only one-twentieth fine gold, as the 12-karat alloy is only half fine gold, and the karat gold shell is only one tenth of the total weight of the article. After years of usage the outer gold layer, originally very thin, may be worn down to almost nothing. Therefore, when estimating its value, "let the buyer beware." Some professional gold buyers refuse to handle this material. ANTIQUES

Very old gold jewelry is sometimes worth more than you would think. Years ago when platinum was cheaper than gold, it was sometimes used as an alloy. It cheapened and stiffened the gold, without increasing its tendency to tarnish, and in rare cases was used in sufficient amount to increase the value of the article. On the other hand, much old jewelry is dishonestly marked, and sometimes you will find that an antique with a handsome exterior is nothing but soft solder inside. FRAUD

Deliberate fraud occurs too often to be ignored. The Jewelers' Circular-Keystone, in its issue of September, 1943, reports one instance. A customer complained that a certain ring, stamped and sold as 14-k gold, blackened his finger. The retailer tested it hastily (by rubbing an edge on the stone and testing the streak) and it seemed to be a full 14-k. But further examination disclosed that about nine tenths of the ring was silver, lightly gilded. Thin circles of 14-k gold wire had been soldered to the top and bottom edges of a heavy silver ring, so that if a touchstone test were made in haste, only gold would rub off. The moral of this is: file

a deep notch if possible, and test more than one surface. Incidentally, the buyer might have been warned by the fact that while this ring bore a karat stamp, there was no maker's trademark—always a suspicious circumstance.

A poorly disguised fraud. Circles of thin gold wire were soldered to the edges of a heavy silver ring, and the combination was gold-plated. The quality stamp was not accompanied by a trademark. Part of the silver ring and part of one gold circle have been cut away.

DENTAL ALLOYS

Metals that have been used in dentistry carry no stamp, and their purity and suitability depend upon the integrity and knowledge of the dental technician. Much dental gold is of high quality, especially inlays and crowns, but in the construction of a denture it is often necessary to use considerable solder, which may be 16-k, 14-k, or even lower. Parts of metal that are covered by vulcanite or porcelain may be of low grade gold or even of base metal, and sometimes rivets of copper or silver are used, then covered over with gold solder. Old fashioned false teeth were, in many cases, provided with two small pins of high-grade iridio-platinum. Much of the work done today, while more satisfactory to the patient, may contain no precious metal at all, so each job must be considered individually. SCIENTIFIC APPARATUS

Enormous amounts of precious metals have been made up into instruments and equipment for the various scientific industries and professions. The laws applying to jewelry apply equally well

to these instruments, and quality stamps and makers' trademarks should always be looked for. In other chapters we learn that in these fields the precious metals may be alloyed with or combined with each other, or with the base metals, in such a profusion of forms that the beginner may well be discouraged. However, no other field is potentially more profitable to the buyer of metals. TREASURE HUNTING IS STILL FASCINATING

These paragraphs may have suggested that this business of buying and selling old precious metals may be as interesting as it is profitable. To find value in a piece of unattractive, unwanted metal brings a thrill of satisfaction over and above the mere gratification of the profit motive. To solve the question of its worth may be as full of unexpected twists as any other puzzle. For instance, we once had occasion to buy a heavy old-fashioned watchchain. Its appraisal seemed to be as simple a task as could be found. We exposed the metal to the oxygen flame; all the links glowed, but three of them glowed with a difference. On closer examination we found that those three links were silver—carved exactly like the others—apparently the result of some old repair job, long since forgotten. On another occasion one section of a discarded penholder, when scraped clean of encrusted ink, turned out to be 18-k gold. . . . Incidents like these help to make this work a constant adventure.

CHAPTER IV

The Platinum-Group Metals and the White Golds SECTION A. NEW METALS; OLD TESTS HEN platinum first came into vogue, it was natural to apply to it the same tests that we use on gold and silver. As we have learned, the old acid and flame tests, described in Chapters I and II, are extremely useful, but they do not always tell the observer as much as he wants to know. Accordingly it is our purpose now to expand these tests, then later to add some new ones, to permit the recognition of many of the alloys of the platinum group that are now in use in the arts and industries. It is only fair to point out while some of these white metals are promptly and easily identified, this is not true of all of them. However, all these tests are well within the powers of the layman who will follow instructions, who is willing to obtain indubitable samples of the various metals, and who will practise with these samples until he learns their characteristics.

W

THE SIX SISTER METALS

Platinum, palladium, and iridium are the more plentiful members of the platinum group, and the ones of greatest general interest. The other three, osmium, rhodium, and ruthenium, are much rarer but are finding increased usefulness as time goes on. These six metals share certain characteristics, notably rarity, white color, density, resistance to corrosion, high melting points, and many chemical peculiarities; but, like human sisters, each has an individuality of its own. Many combinations of two or more of these six, with or without additional metals from other groups, have found employment in jewelry, in many industries, and in the sciences. To explore all such combinations would require much more space than is here available. These chapters, therefore, will concern themselves mainly with those alloys that are of interest to the jeweler and the

old jewelry buyer. These include the two or three kinds of "hard" platinum that form the foundation of the platinum jewelry industry; those alloys of palladium that have found favor in jewelry, including the white golds, and a few of the alloys in which base metals are present by accident or design. Because of their resemblance to the alloys used in jewelry, a number of dental alloys will also be included. WHAT WARS DO TO JEWELRY METALS

When platinum jewelry first came into fashion, early in this century, the alloys generally used were the simple iridio-platinums. (Pure platinum is almost as soft as fine gold, and must be hardened and stiffened for most purposes. The addition of 5 percent to 10 percent iridium gives an ideal alloy for jewelry purposes.) Careful assay of jewelry made at that time may show other elements, but these probably got there by accident because knowledge of how to purify these metals was then far from complete. World War I clamped an interesting economic pincer on platinum. Russia was the main source of supply, and it was cut off by war. At the same time demands increased hugely, both because platinum is used in making chemicals for the munitions industries, and also because the public wanted jewelry made of platinum and did not care how much it cost. Accordingly prices skyrocketed. This situation so stimulated the ingenuity of metal workers that many substitutes and new alloys were devised. Some of these have found honored places in the world of metals, for example, some of the palladium and ruthenium alloys. Some others, in which nickel and other base metals were used, had poor working qualities, and in addition were economically unsound since their complexity caused enough trouble in refining and remelting the scrap to counterbalance the original saving. The fact that we then had no regulations to cover the platinum group served to increase the confusion and to encourage fraud. One of the by-products of the great demand for white jewelry was white gold. The first white golds were gold-palladium alloys, followed shortly by a variety of alloys in which nickel served as whitener. The fact that these alloys came under the gold stamping

laws tended to reassure the careful buyer, and doubtless contributed to their popularity. In England a considerable quantity of palladium jewelry was made during World War I, even though at that time its price was higher than that of platinum. World War II, in its turn, placed restrictions upon most of our metals, and again challenged the ingenuity of the precious metal metallurgist. One expedient, rolled gold on a silver base, was mentioned in Chapter II. During the long Armistice, our chemists and refiners had learned much about the properties and purification of the six members of the platinum group, and supplies of most of them had increased considerably. As a result, alloys and combinations that had been standing unnoticed in the laboratory were escorted forth to make their debut upon the stage of fashion. Thus, when iridium went to war, ruthenium came forward, and the useful ruthenio-platinum was introduced to the jewelry world. In working qualities it so nearly resembles the classic iridioplatinum that its future as a jewelry alloy seems assured. However, "Ruth-Plat," as it is designated by the commercial standard which by this time had been formulated for the platinum group, was in its turn a war casualty when platinum came under restriction. Rhodium also was called to the colors. Finally certain palladium alloys in which ruthenium serves as hardener, received their opportunity, and "jewelry palladium" came into use. When in our mind's eye we review this parade of alloys across the stage of history, we realize that the task of identifying them has become more and more complex. We see why the itinerant gold buyer became confused and decided that it was better for him not to bother with the white metals at all. We see why identification, though more difficult, is far more interesting, and when properly carried out is correspondingly more profitable. (Incidentally, this review brings the practical suggestion that a hint as to the composition of a piece of "platinum" jewelry may sometimes be found in the date at which it was made.) SAMPLES NEEDED FOR TESTING

When we were examining silver and some other white metals in Chapter II, we provided ourselves with samples of as many differ-

ent metals as possible. The serious student will now provide himself with as many samples of platinum-group metals and their alloys as possible. Sets of standard platinum needles, much like the standard gold needles, are on the market, and are useful. These are brass points, tipped with bits of pure platinum, pure palladium, several of the platinum-palladium alloys and an iridioplatinum alloy.

Standard needles for testing platinum-group alloys.

In addition to these, however, or in place of them, you should obtain from a reputable source several sizable pieces of metal—a pennyweight or so of each will be enough for the careful worker— which you will feel free to heat to redness, and from which you can cut off portions to be dissolved in acids, and to which you can apply the various reagents. By all means have pieces of pure platinum, pure palladium, and fine gold. If you plan to distinguish between iridio-platinum and ruthenio-platinum, buy samples of both alloys. The highest grade white golds, which consist of about 85 per cent gold with 15 per cent palladium, more or less, are usually thought of as gold alloys, though they can with equal propriety be called palladium alloys. It is well to have samples of one or two of these. The more samples you have to compare, the greater will be your skill and assurance in identifying unknowns. Mark each sample carefully by stamping or engraving on it some symbol or number. One plan is to have each piece a different shape—square, or oblong, or triangular, or the like—and to make careful record of the composition of each piece.

THE ROUTINE OF TESTING

Let us assume that we have some white metal articles and wish to pick out those made of precious metals and to determine as much as we can of their composition. First we employ the tests described in Chapter II. If the student is not already familiar with these, he should read that chapter again, noticing carefully the references to the platinum metals and the white golds. Thus we use the magnet; we use the air-gas or the oxy-gas flame; we observe the specific gravity or "heft" of the articles; we file deep grooves and apply nitric acid: sometimes we apply plain hydrochloric acid, or plain sulphuric acid, or a grain of table salt. Probably by this time we have separated out the base metals and discarded them, and quite possibly we have formed excellent guesses as to the composition of the more resistant articles. If in doubt, we subject our samples to the same tests, and observe results. THE AIR-GAS OR OXY-GAS FLAME

All manufacturing jewelers, all jewelers who do repair work, and all dental technicians, have air-gas or oxy-gas torches of one type or another. Such a torch properly used is one of the best, as well as one of the quickest devices for the identification of precious metals. As we have suggested in Chapter II, a few seconds spent in bringing a suspected metal to red heat may answer all your questions. The flame will spot the base metal articles for you, and may give you valuable clues to the composition of the precious metal articles. The use of oxygen from a tank, instead of compressed air, has become increasingly common not only for making platinum jewelry, where it is essential, but also for making gold or silver jewelry. For our purposes the oxy-gas flame is preferred. Oxy-acetylene flames are almost as good, but are so hot that they must be used with caution. We have learned in Chapter II that platinum and its precious metal alloys, if brought to white heat and then allowed to cool in air, will show no tarnish whatever, differing therein from most white golds, from sterling silver, and from all the base metals. For

that reason the professional metal buyer normally makes this test the first order of business. For that same reason the established jeweler or dental technician, who has a torch and knows how to use it, is better equipped to buy old precious metals than is the most energetic house-to-house buyer.

One kind of small oxygen-gas blow-pipe.

Much can be learned about a piece of metal by heating it to its melting point—by making it actually molten. For example, iridioplatinum is slower to melt than soft platinum; the more iridium the higher the melting point. If base metals are present, even in small amount, the button that forms on cooling will show a darkened surface and probably will be brittle. An experienced melter can identify the impurities by the stains that form on the crucible. Palladium responds to the flame rather oddly. If you start with cold metal and heat it gradually, you will see films of peacockcolored oxides play across the surface when the metal reaches about 4000 C. At about 8oo° C. these disappear, and if you quench the hot metal in water at the right moment, it will cool before the oxides have time to form again, and the button will be clean and white. The melting point of palladium, 15540 C, is higher than that of gold, lower than that of platinum. Molten palladium absorbs large volumes of gas, and the button swells and puffs; then when it solidifies again the gas is expelled with much spitting and "crabbing." But it is not always possible or convenient to heat your unknown

metals to the molten stage. Sometimes, in fact, you will wish to damage their appearance as little as possible. That brings us to the second section of this chapter, to a series of tests in which a minute quantity of the unknown metal is dissolved in a drop of aqua regia, then treated with some chemical that will reveal its nature. SECTION B. NEW METALS; NEW TESTS If the student has not already done so, he should at once assemble his samples of platinum, platinum alloys, palladium alloys, white golds, and so on, and apply to them the traditional acid tests —first nitric acid, then aqua regia.

So, let us now with our samples of metals and alloys of known composition, make metallic streaks in the cavities of the spot plate, rubbing hard with the hard metals, more gently with the soft ones. Next we shall treat the streaks with nitric acid, then with aqua regia. Following that, whenever such tests do not tell us all we want to know, we shall add some new and additional chemicals, thus carrying out the new tests that have been developed in step with the development of these new alloys. NITRIC ACID AND PALLADIUM

Palladium is the only member of the platinum group that dissolves in nitric acid. Make a streak in a cavity of the spot plate, add a drop of nitric acid, and observe the deep brown color of the solution. Pure palladium is too soft for most commercial purposes. Alloys stiffened with a little ruthenium and rhodium have working qualities suitable for jewelry, and attained a mild vogue during the long Armistice. When, during World War II, restrictions were placed on rhodium, platinum, and ruthenium, the so-called "jewelry palladium" came into quite general use. Several formulas were used, in most of which ruthenium had the role of hardener (with or without the addition of other elements), and some handsome palladium jewelry was made. In most of these alloys the proportion of palladium is so high that nitric acid attacks them at once, showing the brown color. Later in this chapter confirmatory tests for palladium will be described. The inclusion of even a little platinum in a palladium alloy greatly reduces its solubility in nitric acid. Thus the alloy 98% palladium with 2% platinum reacts on the stone like 14-k gold; and the alloy 90% palladium with 10% platinum resists the cold acid completely. Clean the spot plate after each using, dissolving any stain with nitric acid or aqua regia, then rinsing well with plenty of water. AQUA REGIA AND THE PLATINUM METALS

Again make streaks in the cavities of your spot plate, using your platinum-group metals and alloys, your samples of white golds and dental golds, and if possible including several samples of low-

grade platinum alloys—alloys containing copper or nickel or silver, with or without gold or palladium. Mix up some fresh aqua regia. For this work a good mixture is one part nitric acid to four parts hydrochloric acid, and the best container is a dropping bottle. The sketch shows one type of dropping bottle. Notice the grooves on the stopper and in the neck of the bottle; when these coincide you can easily pour out one drop, or as many as you wish, without fumbling or waste.

One kind of dropping bottle. The stopper is grooved, and there is a channel in the neck of the bottle.

Never close tightly any bottle that contains aqua regia. Keep the stopper turned so that the grooves coincide and the gases that evolve may escape. If dropping bottles are unobtainable you can manage with ordinary glass-stoppered bottles and a handful of medicine droppers or small glass rods; but the dropping bottles are much the better arrangement. Add about four drops of aqua regia to each metallic streak, and await results. With some streaks the acid goes to work at once. With others the action is so slow that the hasty observer will conclude that they are not dissolving at all. But sooner or later, depending upon the nature of the alloy and the temperature of the plate, the aqua regia will take on a deeper color and the metallic streaks will disappear. In a notebook write down the order in which the streaks are attacked.

To hasten matters, heat the plate until it is uncomfortably hot to the hand, possibly by placing it on steam pipes, or on an asbestos pad resting on an electric hotplate; or grasp it with tongs and slip it into a pan of hot water. We spoke just now of lower-grade platinum alloys—those containing base metals. Compared with iridio-platinum and ruthenio-platinum, these may dissolve readily in aqua regia, therefore may be confused with certain high-grade alloys in which palladium or gold is present. On the other hand, low-grade alloys containing much silver may be as slow to react as the very valuable "hard" platinums. Thus we see that the mere rate of solution gives only partial information as to the value of an alloy; thus copper or palladium hastens action, while silver, iridium, or ruthenium slows it down, and observations based on speed alone can be quite misleading. This brings us, then, to the modern extensions of this method, whereby it is easy to detect palladium or gold (or both) in a platinum alloy; also to detect platinum, palladium or nickel in a white gold or dental alloy; and to distinguish between iridio-platinum and ruthenio-platinum. First we make a streak with our unknown metal and dissolve it in aqua regia. Then we add certain chemicals to the drop, and by noting the color changes we learn the composition of the unknown. That is the whole story in one paragraph. STANNOUS CHLORIDE TESTING SOLUTION

This solution, often called "Testing Solution A," is extremely useful. Rightly handled it reveals the presence of gold, silver, platinum, iridium and palladium in solution, and suggests the proportions in which they are present. It is easy to prepare and the ingredients are inexpensive. From your supply house purchase an ounce of stannous chloride crystals, and an ounce or less of pure tin metal—mossy, granular, or foil—but it must be pure tin. You will also need some hydrochloric acid, and by far the best container to use is a dropping bottle, similar to that mentioned above. These quantities will provide several hundred tests. Make up only a little of Testing Solution A at a time, as it does not keep well. Take about a pennyweight or less of the stannous

chloride crystals (also called tin salts) in the dropping bottle, add a half pennyweight or so of tin metal, and fill the bottle threefourths full of water. Tap water will do. Now add about 20 to 30 drops of hydrochloric acid, more or less, to a 30 cc. bottle. This gives a milky liquid that is ready to use. The tin metal will dissolve very slowly, and it serves to keep the solution in good condition. Label the bottle "Testing Solution A." As we said, Testing Solution A when properly used shows the presence of precious metals in solution. In order to get acquainted with the color-changes involved, you should first make up some solutions containing these precious metals. You should have a solution containing gold, one containing platinum, and other containing palladium. This method is so useful and fascinating that most users wind up with a whole series of standard solutions, so perhaps you might as well get a half-dozen dropping bottles in the first place. STANDARD SOLUTIONS OF GOLD, PLATINUM, PALLADIUM

To make up a standard solution, simply dissolve a small piece of metal in a little aqua regia, then add water. For instance, take exactly a grain of pure platinum wire; dissolve it in a little aqua regia, using a small porcelain dish and heating gently until all the metal dissolves. Use as little aqua regia as will do the work. Wash the solution with water into a glass-stoppered two-ounce bottle, and fill the bottle up to the mark with water. Label this bottle "ONE GRAIN PLATINUM IN 2 FLUID OUNCES OF SOLUTION."

(When your only object is to become acquainted with the various solutions, it is not necessary to use exact measurements. But later on, when trying to approximate the amount of precious metal in a solution, it will be extremely helpful to have standard solutions made up with a definite weight of precious metal in a definite volume of liquid. Therefore it saves time to make up your solutions in the beginning according to a definite plan.) STANNOUS CHLORIDE TESTING SOLUTION WITH PLATINUM

Let us become acquainted with Testing Solution A. Take the spot plate and drop one drop of the standard platinum solution into a cavity. Notice the pale yellow color. Add a drop or more

of Testing Solution A. If properly prepared the two will react instantly to give a deep yellow or brown color. If too concentrated, the color will be almost black; in that case, dilute the platinum solution with an equal volume of water. This deep yellow color with Solution A is a characteristic of platinum and iridium. WITH GOLD

In another cavity, place one drop of gold solution, and add a drop of Solution A. After several moments add several more drops of Solution A. Note the first intense dark color, deep purple or black. This is characteristic of gold. After it stands a few minutes, notice the purple stain on the white porcelain. Do not let the liquids dry on the plate. Wash it promptly after each test, removing any stains with a drop of aqua regia and rinsing well. Now, in another cavity, take just one drop of your gold solution, and dilute it with five drops of plain water. Take one drop of this dilute gold, in another cavity, and add a drop of Solution A. Note that the color is still definite. Dilute with five more drops of plain water, and try again. See how dilute this gold solution must be before it becomes so weak that you cannot detect a change with Testing Solution A. If you figure this out, you will find that this is a delicate test, one that will reveal the presence of a very small percentage of gold. WITH PALLADIUM

In the same way, learn the color-changes shown when mixing standard palladium solution with Testing Solution A. This colorchange is even more interesting than the others. When the two drops are first admixed, you see a deep yellow, not unlike the effect produced by platinum. After some minutes the yellow turns blue-green. This blue-green color is characteristic of palladium. WITH SILVER

Silver solutions, such as silver nitrate, do not give any color-reaction with Testing Solution A. What you will see when the two are mixed is a white cheesy precipitate of silver chloride, similar

to that obtained when table salt is added to a silver nitrate solution. WITH BASE METALS

Solutions containing only such base metals as iron, copper, zinc, nickel and cadmium give no color change with stannous chloride. Lead may give a white precipitate that looks like silver chloride, but if you employed the dichromate test in Chapter I this will cause you no confusion. STANNOUS CHLORIDE TESTING SOLUTION WITH UNKNOWNS

You should now be ready to examine metals of whose composition you are ignorant. Take an article that you suspect of being platinum or some platinum alloy. Rub it hard to make a good streak in a clean cavity of your spot plate. Dissolve the streak in aqua regia, noting whether or not it is necessary to heat the plate; and making up for evaporation if you do heat it. Add a drop of Solution A and note the color change. Repeat with a piece of what you believe to be a good gold alloy. Repeat with something you believe to be palladium. Finally ask some friend to hand you pieces of metal, preferably pure metals or simple high-grade alloys, test them and check your reports with him. (Testing Solution A must be made up freshly from time to time. It loses its virtue completely in a few days. Therefore, begin the day's work by checking your Solution A against a drop of standard gold solution; if it fails to respond, throw it away at once.) DETECTING GOLD, PLATINUM, AND PALLADIUM, IN THE PRESENCE OF EACH OTHER

The next step is to detect palladium in metal that is mostly platinum. This is especially valuable when testing dental alloys or buying metal that may be contaminated or of low grade. If you have a standard needle of a platinum-palladium alloy, rub it on your spot plate, warm the plate, dissolve the streak in aqua regia, and test the solution with Testing Solution A. Can your eye detect the difference between that effect and the effect produced by pure platinum?

Next, rub pure platinum in a cavity, and make a few rubs in the same cavity using a bit of fine gold. Suppose you make fifteen rubs with platinum, and three rubs with gold. Again warm the plate, dissolve the streaks in aqua regia, and test with Solution A. Can your eye detect the presence of that small amount of gold? Also, can your eye detect the presence of all three metals—gold, platinum, and palladium—at the same time, in a single drop of solution? Your eye may not be able to do this the first time. But after a little experience, you will know which metals are present and roughly the proportion of each. Skill in appraisal comes with practice—practice in studying the behavior of alloys of whose composition you are certain, exposing them to the various tests and comparing them with each other and with unknowns handed to you by some friend who can check your reports. If a spot plate is not obtainable, it is possible, though not convenient, to use other plans. Thus, get a minute amount of your unknown metal into solution in some other way, perhaps by cutting off a scrap with a file or saw and dissolving it in aqua regia in a tiny test tube or small watch glass. Soak up the solution in clean white blotting paper or filter paper. Now drop one drop of Testing Solution A onto the stain. Colors will appear and spread through the paper handsomely. If two precious metals are present, say gold and palladium, the characteristic colors of both will appear. IF THE TESTS ARE NOT CONCLUSIVE—

The beginner sometimes gets confusing results. Sometimes the colors refuse to appear. This may be due to the fact that one solution or another has lost its potency. More likely it is because you have used too much acid. Remember that aqua regia weakens on standing. Remember that Testing Solution A spoils on standing. Both must be mixed afresh from time to time. The standard solutions do not spoil. If properly kept in glass-stoppered bottles they will keep for years. But when you make them up, do not use an excessive amount of acid to dissolve your bits of metal. If too much aqua regia is used, the tests will be weakened or even destroyed.

The excess acid can be driven off by evaporating the solutions gently until sirupy, then adding a little water. In dissolving the streaks made on the spot plate, you sometimes use more aqua regia than is wise. There again you can remove the excess by warming the spot plate gently; if the drop should go entirely dry, add plain water to bring your substances again into solution. Another situation that may confuse the beginner is to find an alloy containing much platinum and very little palladium; or much gold and very little palladium. He finds that the palladium color is obscured by the intense reactions of the platinum or the gold. As his eye becomes skilled he can detect smaller and smaller proportions; however, he will be glad to know that there is another solution that is especially valuable in detecting small amounts of palladium. DIMETHYL GLYOXIME SOLUTION

This solution has the added virtue of showing up nickel, even in small amounts. It will show up nickel in a platinum alloy; in a white gold alloy; in a dental alloy; or in a solution. It will show up palladium and nickel when both are present in small amounts in an alloy that is largely platinum or gold. Purchase a gram of dimethyl glyoxime. One gram will be enough for several hundred spot plate tests. Be sure to get a good quality product. It is a white or pale yellow powder. The name is pronounced "dye-methyl glyoxeem," but no one will blame us if we refer to it as DMG. Dissolve this gram of DMG by bringing it to a boil in about 100 cc of water—about 4 fluid ounces. The powder dissolves rather slowly. Let it cool and if possible let it stand overnight; then filter. It is important that the solution be clear and free from sediment or crystals. It is now ready to be placed in a dropping bottle, which should be labeled DMG. It keeps quite well for years, except that you may have to filter it again. Let us get acquainted with DMG. Its most interesting characteristic, as we said, is to show up palladium and nickel, in the presence of other metals and in the presence of each other.

DMG AND PALLADIUM

First, place a very small drop of the standard palladium solution in a cavity of the spot plate. Or, better, take one drop and dilute it with several drops of water to obtain a pale yellow solution; then place one drop of the pale solution in a clean cavity. Do the same thing with a drop of your standard platinum solution, and with your standard gold solution; a drop to a cavity. All three have a pale yellow color. Now add a drop or two of DMG to each cavity. Note the PRECIPITATE that forms, and its color. Note that the pale yellow colors do not change, but that in the cavity containing palladium you will see a PRECIPITATE, or sediment. Note carefully that while Testing Solution A gives prompt changes in color, DMG distinguishes between palladium and the other metals by forming a precipitate. You can see this more clearly by making similar tests in small test tubes. Make one test with an extremely dilute palladium solution, adding DMG and noticing that even very small amounts of this yellow precipitate are visible. Be sure in the beginning that all your test solutions are clear and free from precipitates or flocculence; otherwise you will be deceived. DMG AND NICKEL

Scratch on the spot plate with a five-cent piece. Dissolve the streak with a drop of nitric acid or aqua regia. Add a drop or two of DMG. Nothing special will happen. Now, add a big drop of ammonia. If you used enough ammonia to kill the acid, you will see a very beautiful and characteristic color change. From one point of view it is a waste of time to describe these color changes, since they become of value only through being seen by each observer. However, for the sake of the record we may say that this color, produced by DMG, nickel, and ammonia, is a striking rose-red. And the precipitate produced by palladium and DMG in acid solution is canary yellow. Note this particularly: The test for palladium appears only in ACID solution; the test for nickel must be made in AMMONIACAL solution.

This is very handy. Thus, suppose you have a piece of so-called platinum as an unknown, and you suspect that it may contain both nickel and palladium. First make the streak on the spot plate and get it into solution with aqua regia. Then add DMG. If palladium is present you will see the copious precipitate, canary yellow in color. Now add enough ammonia to make the mixture smell faintly. If nickel is there, you will at once see the beautiful rose-red. All in one cavity of your spot plate. Continue to test various scraps of metal, such as cheap white gold, (which is almost sure to contain nickel) and high-grade dental alloys, (which are almost sure to contain palladium). These tests are so fascinating that it will be no hardship to practice until your eye is quite thoroughly trained. THE SPOT PLATE AND AN UNKNOWN

With the facts already learned, the clever observer is now ready to test a wide variety of unknown metals. Suppose you have a piece of jewelry, and you suspect it of being palladio-platinum, possibly containing gold and nickel. Let this diagram represent the cavities in the spot plate: o o o

o o o

o o o

o o o

Now make scratches with your unknown in the three cavities to the left. Make from 10 to 25 scratches in each cavity; with soft metals a few scratches are enough; with hard ones use more. Count the scratches, so as to use the same number every time in a given test. In the second row of cavities, make scratches with some metal of known composition, whose nature you believe to be similar to your unknown. Let us call this alloy a; the unknown will be called x. Thus, suppose you suspect your unknown of being approximately 20-80 palladio-platinum. In that case, the second scratches should be made with a needle of that composition. In the third row of cavities, make scratches with some other

combination of metals, which you suspect may resemble your unknown x. For example, you might make fifteen scratches with pure platinum and five scratches with fine gold. Call this alloy b. In the fourth row it might be useful to make scratches of some further combination which may or may not resemble x. For example, make fifteen scratches with pure platinum and five scratches with a piece of pure nickel. Call this c. Your spot plate will now look like this: xo xo xo

ao ao ao

bo bo bo

CO CO CO

The next step is to dissolve every one of these streaks in aqua regia. With platinum alloys you must heat the plate. Into each cavity drop exactly the same amount of aqua regia. Give the streaks time to dissolve; indeed, you can gather considerable information regarding your unknown by noticing the promptness with which it dissolves in aqua regia. In some cases the color may prove helpful; you will recall that both copper and nickel give green solutions; unfortunately gold, platinum, palladium and iridium all give the same color here—yellow. After the streaks have all dissolved, begin your tests. Starting at the top, place about three drops, more or less, of Testing Solution A in each of the four top cavities. Now, to the middle row of four cavities, add two or three drops of DMG. Use the same number of drops in each cavity of a row. In the bottom row, add first a big drop of ammonia, then one or two drops of DMG. Compare the way in which your unknown responds to these tests, with the reactions caused by alloys or mixtures whose nature you are sure of. Sometimes it helps to let the spot plate stand a while—half an hour, or overnight. New colors may appear. If your unknown is strikingly different in its reactions from your knowns, then start in all over again, after cleaning your spot plate, using another set of knowns. These suggestions will readily bring to mind other possible arrangements. The success of this method lies in practice, care, a good memory and a good light. Also in keeping your spot plate clean.

To DISTINGUISH BETWEEN IRIDIO-PLATINUM AND RUTHENIO-PLATINUM

In some ways this test is more difficult than most; hence it is essential to practise with samples of both alloys until you are sure of the method. You will use the spot plate, aqua regia, some fullstrength C.P. ammonia, and a few crystals of sodium thiosulphate— also called "hypo" and obtainable from any photo or chemical supply shop. First make thirty scratches in a cavity of the spot plate with the iridio-platinum. In another cavity make thirty scratches with the ruthenio platinum. Heat the plate as usual, and dissolve the streaks in aqua regia. However, since these alloys are so slow to react, you probably will have to add more aqua regia, a drop at a time, to make up for evaporation. Do not let the cavities go dry; it may help to add a drop of water. It usually takes about ten minutes for the streaks to dissolve. Sometimes the particles of metal float loose from the porcelain before they really dissolve. Keep the plate hot. When all the metallic particles have dissolved, add to each cavity two or more drops of ammonia—enough to make the solution definitely ammoniacal. Warm again, being careful not to let the spots go dry, adding a drop of water or of ammonia to keep things in solution. Finally, add to each cavity a small crystal of sodium thiosulphate (hypo). In the ruthenium solution you will see a red or pink color within two or three minutes. Compare it with the iridio-platinum solution, which shows almost no color change. That is all there is to the test. Its only difficulty is that these alloys dissolve so slowly, even when the plate is hot, that some observers lose patience and give up before the test has had time to act. Also, it is necessary to keep the spots from going dry, and this requires some watchfulness. This reaction was reported first by Carey Lea, and its use for this purpose was suggested to the writer by Raleigh Gilchrist of the United States National Bureau of Standards.

SECTION C. SOME OTHER TESTS There are many other tests used by chemists and metallurgists for the identification of metals. Those already given will serve most purposes. The following tests, however, are included in this chapter because of their long usage and for their value in special applications. IODINE TEST FOR PALLADIUM

Place a drop of tincture of iodine, the kind found in most family medicine kits, on a piece of palladium or an alloy that is rich in palladium. Heat with a small flame—-a match will do—until the alcohol in the tincture takes fire and the liquid dries. A black stain of palladium iodide will remain, to be removed only by vigorous rubbing. Repeat, using platinum or a nickel-gold; while a stain will form, it is less deeply colored and can be easily rubbed off. THE GLOW TEST

One peculiarity of the platinum group metals is their ability to soak up gases. This is utilized in one kind of cigarette lighter, in which some finely-divided palladium can be exposed to naphtha fumes; it soaks up the fumes and in so doing becomes hot, and finally the fumes ignite. This phenomenon can be used as a test for platinum group metals in some cases. However, many substances inhibit the test, while others (such as copper) may produce a false glow, so the test has fallen into disuse, and is not recommended for our purposes. ANOTHER TEST FOR GOLD

Ferrous sulphate (also called copperas) is often used as a test reagent for gold in aqua regia solution. Before making the test, heat the solution gently almost to dryness and add a little plain hydrochloric acid, then again evaporate almost to dryness. This is to remove all excess nitric acid, whose presence interferes with the test. Now add a little water and a crystal of the pale green ferrous sulphate, and after a few seconds a dark cloud of finely divided metallic gold will appear.

ANOTHER TEST FOR PLATINUM

In the refining and purifying of platinum, it is customary to add ammonium chloride to an aqua regia solution of the metal, and a yellow powder will precipitate out. This powder, whose color ranges from canary yellow to deep orange, is platinum-ammonium-chloride. It is collected and converted back into metallic platinum. This same reaction can be used to identify platinum. Dissolve a scrap of metal in a little aqua regia. Dissolve some ammonium chloride in a little water to make a concentrated solution, and add it to the acid solution. Watch for a yellow or orange precipitate. Practise with your platinum samples before attempting to identify unknowns. You will find that this test is not as delicate as some others, for if there is only a little platinum in solution, no precipitate will be visible. Some people add the ammonium chloride as a dry salt; this is not wise, for you may mistake its crystals for the yellow powder that you are seeking. Potassium chloride can be used in this test instead of ammonium chloride. This test is a favorite with prospectors, and is dependable when properly used. However, wishful thinking has led at least a few workers to mistake sand and other worthless materials for the yellow or orange precipitate. It is wise to practise with several ores and minerals known to contain platinum, before attempting to identify unknowns. OLD AQUA REGIA SOLUTIONS

Men who work with the precious metals have frequent occasion to dissolve them in aqua regia, for example as the first step in the preparation of a gilding bath, or in the refining of factory wastes. It is not unusual to find accumulations of these old solutions, sometimes heavily contaminated with other metals. Methods of appraising such solutions differ with circumstances, but in general we utilize the principle discussed in Section B of this chapter. That is, drop-size samples are tested in the cavities of the spot plate against the various testing solutions until the components are established. Then by comparison with the Standard Solutions (in which a known weight of metal is dissolved in a known volume of

liquid) we can roughly estimate the weight of metal in a given volume of unknown solution. This calls for skill and patience, the drop-size samples being diluted with one or more drops of water until the intensity of the color-reactions of the unknown solution approximate the intensity of the color-reactions given by the Standard Solutions. This problem, which is hardly one for the beginner, is discussed in more detail in the book Refining Precious Metal Wastes, by C. M. Hoke, published by the Metallurgical Publishing Company, 123 William Street, New York. TESTING ALKALINE SOLUTIONS

You will observe that in the tests so far described, the solutions have been mildly acid or neutral. Never strongly acid—excess acid will weaken or even ruin most of them—nor alkaline, except in those cases where an ammoniacal solution was used. Testing Solution A will not work at all in alkaline or cyanide solutions, until the alkalinity is destroyed. Thus, suppose you have an old cyanide gilding solution, and wonder if it contains dissolved gold: Take about five drops of the suspected liquid in a small test tube or tiny dish, stand near a window or an exhaust fan, and carefully add four or five drops of hydrochloric acid. The fumes evolved are extremely poisonous—hence the need for working near an exhaust. Bring the mixture cautiously to a boil; this drives off the cyanide. Let it cool, and you can now use Testing Solution A or ferrous sulphate the same as usual. Success with all these tests calls for practice, patience, and a good light. It also requires keeping your spot plate clean. ELECTROGRAPHIC TESTS

A clever electric method for detecting gold, chromium, and some other metals in alloys or electrodeposits has been worked out by J. A. Calamari, Robert Hubata, and P. B. Roth of the New York Medical Laboratory in Brooklyn. The test is easy to perform* need not injure the article, and requires only simple equipment. The article to be tested is wired to the positive pole of a battery, 6 to 9 volts, and a pad of filter paper or white blotter, wet with a solution of sodium nitrate and hydrogen peroxide, is laid on it. A graphite rod connected to the negative pole is touched to the wet paper.

If the paper is in contact with gold, a purple spot appears. Most base metals give no reaction, but chromium gives a blue spot, silver a black spot, and so on, and the intensity of the color may suggest the karat or composition of the surface layer. The method is described fully in Industrial and Engineering Chemistry, July 16, 1942.

For our purposes this method has the disadvantage of centering attention on the surface of the article, which as we know may be quite different from the bulk of the piece. But when properly applied and understood, it is very useful. SPECIFIC GRAVITY

Even in prehistoric days people noticed that some metals were heavier than others, and that the precious metals in general are heavier than the common ones. These differences are utilized in many ways; thus the prospector shakes the gold-bearing gravel in a pan, with water, and the heavier gold particles settle to the bottom. These differences have also been used, for centuries, in identification and appraisal. The story is that Archimedes, a Greek mathematician of the third century B.C., was asked by his king to determine if a crown, purporting to be gold, did not actually contain some silver—a problem of precisely the type that confronts the readers of this book. Archimedes was puzzled, until one day as he stepped into his bath and saw some water overflow, it came to him that the excess of bulk caused by the introduction of a lighter alloying element could be measured by putting the crown and equal weights of gold and of silver, separately, into a bowl of water, and noting the difference of overflow. The story continues that Archimedes was so overjoyed at this happy thought that he ran home without his clothes, shouting "Eureka! Eureka!," meaning "I have found it!" This ratio between the weight and the bulk of an article is called its density or its specific gravity—"specific" because each pure elemental material has its own unique and specific ratio. The procedure for determining it is given in the Appendix. Pure water is commonly used as a standard of comparison, with the specific gravity of 1.00. A cube of water measuring 1 centi-

meter on a side weighs 1 gram. A cube of gold of the same size weighs 19.32 grams, and has a specific gravity of 19.32. Silver, lead, palladium and mercury occupy a middle group with gravities running from 10 to 13. Tin, zinc and steel are all close to 7; aluminum is 2.7; platinum is 21.37. Gases, and things like cork that float on water, have specific gravities of less than 1, usually represented by a decimal. Alloys have densities that range between those of the components. Thus a palladio-platinum alloy will come somewhere between pure platinum and pure palladium, and its specific gravity will suggest its composition. Sterling silver can be distinguished from silver alloys of lower grade. Iridio-platinum can be distinguished from ruthenio- or palladio-platinum. High karat golds are heavier than low karat. And so on. However, the method has its limitations. For example, by manipulating the components it is easy to make up several alloys of the same density but different compositions. If a bar contains bubbles or blow-holes its density will be less than that of a homogeneous bar. If such a bar were drastically rolled its specific gravity would increase. If a piece of jewelry contains stones, these must be removed before a significant specific gravity determination can be made. In general, the smaller the article, the less accurate the determination. In the Appendix will be found a list of metals with their densities and melting points, as well as their responses to nitric acid, to hydrochloric acid, and to the oxy-gas flame.

CHAPTER V

Buying and Selling Old Precious Metals

C

AN I make money buying and selling old gold? "Where can I buy it?" "To whom can I sell it?" "Must I have a license?" "How much is this old silver worth? This platinum? This palladium?" "What is the most profitable kind of old precious metal to handle?" "Will it pay me to buy up a lot of old filled watchcases and plated spectacle frames?" "Is it true that this line is full of grafters?" "I paid eighty dollars for this watch; why is it the jeweler will give me only three dollars for it now?" These and other related questions come up repeatedly. This chapter will try to reply to them, and to be helpful both to the layman (or lay woman) with some jewelry to sell, and to the jeweler or antiquarian who might buy it. THE FOUR STEPS

There are four steps in the process of buying and selling old precious metals. First the metal must be identified. We make sure that it is gold and not brass, and we determine its karat quality as accurately as we can. Or we make sure that it is silver all the way through, and not silver plated. Or we decide that it is platinum of high quality; or of low quality. The details of this first step have been described fully in the first four chapters of this book The second step is to find out how much the article weighs. The final steps are to calculate its value and to find a purchaser who will pay the highest price. Let us now consider these steps in turn. WEIGHING PRECIOUS METALS

We often see pictures of Justice holding a balance in her hand. But in real life we get much more just results if the scales are sup-

ported on a strong and rigid frame, carefully leveled so that the beam, when at rest, lies truly horizontal. Indeed, the use of a hand balance in trade is generally forbidden by law, for a clever swindler can tip a hand balance in his favor, and even an honest hand can be unsteady. The troy system of weights is commonly used with the precious metals. Its basic unit, the grain (gr.) is of the same weight as the grain used in the apothecaries' and avoirdupois scales. 24 grains = one pennyweight (dwt.) 20 dwt. = one troy ounce (oz.) 12 troy oz. = one troy pound (lb.) The pound is rarely mentioned, which is just as well, for it differs just enough from the generally-used avoirdupois pound to make for confusion. For small quantities there is a growing tendency to use decimal parts rather than to mention two units. Thus, instead of saying 20 ounces 10 pennyweight, we might say 20.5 oz. Instead of 15 pennyweight 6 grains, we might say 15.25 dwt.

The seller must remember that a swindler can use an honest balance but dishonest weights. Some of the itinerant old-gold buyers that flooded the land during the depression of the '30's were said to use a copper cent, weighing about 50 grains, instead of a pennyweight (24 grains), thus obtaining twice as much gold as they paid for. The difference between the troy ounce (480 grains) and the lighter avoirdupois ounce (437.5 grains) has also been used to the disadvantage of the unwary. As we said, the troy system is in general use with all the precious metals. However, scientific workers, accustomed to the metric system, like to buy and sell their platinum group metals by the

gram or milligram, and the well-equipped metal buyer will have a set of gram weights in addition to his troy weights. A good balance is a sensitive and expensive instrument. It should be sheltered from dust and draughts, and must stand on a firm level table, free from vibrations. Weights should be kept in a covered container, and should be picked up with tongs made of a relatively soft metal—never touched with the fingers. You can learn something about a person and his establishment by observing how he handles his balance and weights. THE "OLD GOLD" INDUSTRY

For generations—until the depression of the 1930's—the buying and selling of old gold had been an inconspicuous industry. The sums involved were small, and there were only a few simple regulations. Few jewelers sought such business, and when it came to them they carried it on apologetically in the back office. Then, after Great Britain went off the gold standard, the picture changed. The purchasing power of gold began to rise all over the world. Prospectors got out their rusty shovels and went into the hills. Itinerant gold buyers went from house to house picking up unused trinkets. In 1933 the United States called in all gold coins, and our gold price, which for years had been $20.67 an ounce, started the step-by-step climb that finally was pegged at $35 an ounce by the Gold Reserve Act of 1934. With this increase in value—a rise of almost 70 percent—the old gold business mushroomed into an important industry involving thousands of people and millions of dollars. Jewelers hung the "We Buy Old Gold" sign prominently in their front windows. Socalled refiners' agents opened up on every Main Street, while house-to-house canvassers swarmed over the country by the thousands. Some of these latter were honest and intelligent, but many were patently dishonest, and most of them were deeply ignorant of metal values. (For example, since their main interest was in the yellow metal, gold, few of them learned how to appraise platinum and white gold, or even to recognize them.) This feverish and unwholesome activity was finally calmed, partly by legitimate competition, partly because federal and local regulations put the fly-by-night and the crook out of business.

Since then the buying and selling of old precious metals has been stabilized on a higher plane, and is now largely in the hands of men who, like jewelers, have a knowledge of metals and integrity in handling them. FRAUDS AND MISUNDERSTANDINGS

No doubt there has been much deliberate deception in the handling of the precious metals. There have also been many honest mistakes. This book has repeatedly mentioned certain necessary precautions—allowances for solder, the need to penetrate into the inner layers of metal; stainless steels that resist the usual acid tests; the wisdom of testing white and green golds with white and green gold needles; the wisdom of testing all parts of complex articles such as watchcases, and so on. It is indeed true that such precautions are needed, as was revealed some years ago when several jewelers, men used to handling gold, were deceived by stainless steel. The experienced jeweler tends to judge the worth of an article by the workmanship upon it—if the workmanship is good, he expects the metal to be worthy. This tendency has been traded upon by a few unscrupulous persons, and fake antiques, of excellent design and craftsmanship, have appeared on the scene. However, for every single instance of this kind, there are thousands of honorable transactions. Some of these latter, however, have been misunderstood by the layman. Thus: A woman brings in a watch, now useless, but once highly prized; the jeweler offers her a few dollars, representing only the old metal value; he can give her nothing for the mechanism, nothing for the labor originally put into the case, nothing for the fashion element that once accompanied it, and not a cent for the profit that the original dealer made when he sold her the trinket. Situations such as this often mean disappointment to the seller, but reflect no discredit on the buyer. "WHO WILL BUY MY GOLD?"

The layman with a few pennyweight of gold will generally do best to take it to a neighborhood jeweler of good repute. Large lots probably should be sold to Uncle Sam. If his community has no jeweler, his bank will advise him as to the financial stability of

someone nearby. A jeweler will explain the value of the metal, and if there are any precious stones he may purchase them as well. If the article has artistic merit the jeweler may indeed pay more than the mere old-metal value and purchase the article for re-sale. The professional refiner sometimes—not always—will pay a few more cents a pennyweight than the jeweler. However, he rarely is interested in artistic merit nor in precious stones. There are professional refiners in most large cities, and their agents can be found almost everywhere and are usually glad to be of service to the layman. The retail jeweler who buys old precious metal will sell it to Uncle Sam or to a professional refiner, his choice being governed by considerations that will be discussed later in this chapter. The manufacturing jeweler will probably refine his purchases and use the metal in his own shop, or perhaps he will turn it in in exchange to the metal dealer from whom he buys his raw material. When jewelers buy old gold from the public, the appraisal is normally made on the basis of the quick tests with acid and touchstone that have been described in these chapters. When the Government buys gold or gold-bearing material, it melts down every lot, mixing it thoroughly, takes a sample and assays it carefully. Payment is made on the basis of this assay. This procedure takes a few days, but naturally gives an accurate valuation which leads to greater satisfaction all round. Very small lots are not accepted. When refiners buy metal, they usually employ the quick touchstone tests for small lots, while large lots are melted together, sampled, and assayed. U. S. GOVERNMENT REGULATIONS

The regulations imposed by the United States Government were designed originally to prevent hoarders who in 1933 had violated the law by failing to turn in their gold coins at the old value, from profiting when the price of gold was increased. These regulations now apply to all transactions involving any substantial quantity of gold, and have proven of great protection to the public and the legitimate dealer. During World War II all the metal industries, both base and

noble, underwent many changes due to shortages and war restrictions, and more regulations were imposed, mostly on the manufacture of specific metal articles. Since all such regulations are subject to change, it would be idle to repeat them here. The interested reader should obtain copies of current regulations from time to time, as he needs them, from his nearest Federal Reserve Bank, or the Mint or Assay Office of his district. For many years the regulations regarding Uncle Sam's purchases of gold were quite simple; he would purchase gold in almost any form from anyone, and no questions asked. Each lot had to be of a certain minimal quality and total value. A small charge was made to cover the refining of the material, the rates varying slightly from time to time. Shipments were made by hand or express to the owner's nearest Mint or Assay Office. The government has never employed any traveling agents, and has publicly stressed the point that the Mint has no agents soliciting for it. "MUST I HAVE A LICENSE?"

Since we went off the gold standard, the regulations now involve the licensing of those who acquire, transport, melt or treat, import, export, or earmark gold in substantial quantities, or hold it in custody for foreign or domestic accounts. The rules regarding Uncle Sam's purchases of native gold, old jewelry, etc., have also been modified in almost every detail. These rulings are subject to further change without notice. Several kinds of licenses are provided—all being described fully in the Regulations. Application forms for the various licenses can be obtained from the Office of each District; these must be filled out in duplicate and sworn to before a Notary Public, and returned to the Office of the District, with such further information as the Regulations require. No charge is made, and in general if a man has been established in some branch of the precious metals industry or has legitimate need for gold, he will not be refused a license. One of the requirements of licensees is that they should not do business under a name which would induce the belief that gold is being handled on behalf of the Government or for the purpose

of carrying out any policy of the Government. In other words, Uncle Sam does not want gold-buyers to pose as his agents. Many states and cities require local licenses in addition to the Federal license. Local regulations are aimed at preventing the sale of stolen goods and the fleecing of uninformed sellers. THE MINTS AND ASSAY OFFICES

The Denver Mint takes care of applicants from the following states: Colorado, Iowa, Kansas, Minnesota, Nebraska, New Mexico, North and South Dakota, Oklahoma, Texas, Utah, and Wyoming. The Assay Office at New York takes care of Connecticut, Delaware, Maine, Massachusetts, Michigan, New Hampshire, New Jersey, New York, Rhode Island, Vermont, and Wisconsin, Puerto Rico, Virgin Islands, and Canal Zone. The Philadelphia Mint takes care of Alabama, Arkansas, Florida, Georgia, Illinois, Indiana, Kentucky, Louisiana, Maryland, Mississippi, Missouri, North and South Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, and the District of Columbia. The Seattle Assay Office takes care of Idaho, Montana, Oregon, Washington and Alaska. The San Francisco Mint looks after Arizona, California, Nevada, and the territories and possessions not otherwise mentioned. UNCLE SAM DOES NOT BUY PLATINUM

One government regulation of peculiar interest is that covering the platinum-group metals. The Mints and Assay Offices do not wish them and, if they are included in a shipment Uncle Sam will not pay anything for them. In fact, his refining charges will be that much higher, because of the extra labor involved in assaying and refining material that contains these metals. The moral is plain—sell your platinum to one of the many dealers who will pay a fair price for it. This metal will be discussed again in this chapter. WHAT TO DO WITH SILVER

At certain times in our history Uncle Sam has bought silver as well as gold. The world price fluctuates from day to day, being

influenced by political and financial conditions at home and abroad. Quotations will be found in the daily papers. Meanwhile, though silver is not high, there is a good market for it, and if one has a quantity of old sterling silver he can sell it to a professional refiner, especially one who is equipped to make it into sheet, wire, or the like, and to sell it for making up new goods. Several refiners specialize in silver, and silver is always accepted by the Government as an integral part of a deposit of gold that complies with its regulations—that is, silver that serves to alloy the gold. Silver plated ware is of such small value today that in general it is not traded in except by those who happen to have many pounds of it. Usually this is sold to a copper refinery, where it goes through the same electrolytic process that is used in refining copper; the silver is recovered as a by-product. "How MUCH IS PAID FOR OLD GOLD?"

At present writing, the Government price of fine gold is $35.00 a troy ounce, or $1.75 a pennyweight. Ordinary gold contains more or less base metal, and is worth correspondingly less. There is always a "spread" between the buying price and the selling price of any article, to provide for the handler's living, and gold is no exception to the rule. Previous chapters of this book have told how to establish the karat or quality of a gold article, and how to establish whether a given article is solid gold or merely gold filled or plated. An experienced purchaser will allow a leeway of one or two karats, for solder or for errors in testing. That is, suppose a ring seems according to the touchstone test to be a full 14-k; he will study its design to see whether it required much or little solder, and possibly he will decide that the ring as a whole would assay 13-k. As mentioned in earlier chapters, chains and mesh usually have more solder per unit of weight than other articles, and a chain whose links are 14-k may assay 10-k to 11-k. THE GOLD-BUYER'S ROUTINE

Here is a procedure that probably would be followed by a jeweler when buying gold in small quantities with the expectation

of selling it eventually to a refiner. He establishes its average karat; finds the weight in pennyweights; then multiplies the karat times the weight times about 5^ to 51/^ for the purchasing price. He can expect the refiner to pay him about 6^ to 61^^. (These figures are all based on fine gold at $35 per ounce.) For example: An old ring mounting seems to be 14-k on the touchstone; the design requires very little solder and there are no indications that repairs have been made. Assuming that the average quality would be at least 13-k, and noting that the weight is 3 dwt., he multiplies 13 x 3 x 51/2^ The answer is $2.14^4, and represents the price he would pay to the seller. He hopes to sell the article to a professional refiner for 13 x 3 x 61^^, or $2,531/2The difference of 39^ is his profit and must pay for his time in making the touchstone tests, the cost of shipping to the refiner, and so on. By buying for a little less than 51/^ sometimes, and occasionally selling for a bit more than 61/2^ the profit may run from about 18 percent to 30 percent on the investment, with 25 percent as an average. To the jeweler, this transaction has another aspect. It has led someone to enter his store and make his acquaintance. The profit may well be small, but it often leads to further business with a larger return. For this reason many jewelers figure on a very narrow "spread" between the buying and the selling price of their old gold business, and thus build up good will. On the basis of 6i/2<j; per karat per pennyweight, a refiner would pay 65^ for a pennyweight of 10-k gold, $1.23 for a pennyweight of 18-k gold, and so on. When a refiner buys a large quantity of clean old jewelry or scrap, enough to justify a chemical assay (instead of an appraisal based on touchstone tests) he may pay more than 61/2$ per karat per pennyweight. Some kinds of old metal are more difficult to refine than others, because of the quantity and nature of the base metals present, and this factor also may affect the price. FILLED, ROLLED AND PLATED GOODS

Gold filled and rolled gold stock, so much of which is used in spectacle frames, watch cases, and moderately priced jewelry, is much less valuable. It may bring 25^ to 75^ an ounce. It is im-

portant to remove all nonmetal or base metal parts before weighing. Note that this price is for an ounce, not a pennyweight. Gold plated stuff is worth even less; possibly io^f to 15^ an ounce. Uncle Sam does not buy it, and most refiners receive it without enthusiasm if at all, except when very large lots are available. BUYING AND SELLING PLATINUM GROUP METALS

The market for old platinum metals is not as well standardized as that for gold and silver. The Mints and Assay Offices do not buy these metals from the public. The layman with a few pennyweight of platinum jewelry to sell will generally do best by taking it to his neighborhood jeweler, if possible to the one from whom it was originally bought. The jeweler or old-metals buyer should seek a refiner who is active in this market. Certain refiners specialize in these metals, while others specialize in gold or silver. Makers of scientific apparatus, dental supply houses, or jewelers who use platinum in the manufacture of their wares, should also be considered. Since these metals have many wartime applications and have at times been under restriction, enquiry should be made as to the legal aspects of any sale or purchase. These metals normally have fluctuating prices. Quotations may be obtained from dealers or from trade papers. At certain times the Government has established fixed prices. As we learned in Chapter IV, some of these metals are easily identified, and thus easily appraised, but many of the alloys and combinations are fairly difficult to identify, and even more difficult to appraise. Several different alloys or combinations are used in jewelry, and in the various technical fields the number of alloys and combinations, with or without gold or silver or base metals, is legion. These all look a good deal alike but differ widely in value. The situation is further complicated when a base metal core is completely encased in only a thin shell of precious metal. A complete chemical assay for the exact determination of these metals is longer and more costly than one that involves only gold or silver, and becomes increasingly difficult with each additional element to be determined.

The refining of scrap or waste metal for the recovery of these metals, and the purification that may be needed to prepare them for resale, are in general more time-consuming than similar tasks in which only gold or silver are to be recovered. And there are fewer workers qualified to do such work. THE PLATINUM "SPREAD"

Because of the complications just described, the "spread" between the buying and the selling prices of the platinum-group metals and their alloys is wider than the "spread" for gold or silver. Thus, when a prospective buyer is calculating what to pay you for your scrap platinum-group metals, he recalls the difficulties of identification and appraisal; he remembers that a complete assay may be a slow and expensive job; he reflects that it may not be easy to refine and repurify what he buys; and he recalls that the market price of these metals may suddenly drop. Accordingly he quotes you a buying price that will be low enough to take care of all these factors. And when he comes to sell the refined metal again, his selling price must be correspondingly high. Sometimes one can return scrap platinum, such as old chemical ware, to the original dealer from whom it was bought. If so, and if the article is still in recognizable form, he may well offer a higher price than usual, since he knows its composition and need not figure in the cost of appraisal and testing. METALS USED IN DENTISTRY

Yellow gold fillings are high quality gold—22-k or so. The modern cast fillings are sometimes of lower karat. Dentists often place fillings of much less expensive materials in the back teeth, where they will not show; some of these turn dark or even black. From the standpoint of the patient's benefit these fillings are often of the highest value, but to the old-gold buyer they are not attractive. Old fashioned false teeth were, in many cases, provided with two small pins of high-grade iridio-platinum. Much of the work done today may contain no precious metal at all, so each job must be considered individually. Many of the dentures of today are made of gold-platinum-palladium alloys, some of which at times are worth more than fine

gold. They often look like so much nickel, being white or of a slightly yellowish white color, but a few of the tests described in this book will quickly prove their value. Scrap metal of this type can, in general, be sold to best advantage to a dealer in dental alloys, since he can most easily appraise it. "ARE WHITE METALS THE MOST PROFITABLE TO TRADE IN?"

It is being said that platinum, white gold, and the whiter dental scrap are the most profitable part of the "old gold business" today. This will doubtless be the case for some time in the future. For one reason, most of the early house-to-house canvassers did not know how to identify platinum or palladium, and distrusted any whitelooking alloy, and therefore refused to purchase many very valuable offerings. This led the owners to place a lower value on such articles. Accordingly when a buyer appears who knows how to judge such metals, he can pick up excellent bargains. The reader may have wondered why so much space was devoted in this book to methods of identifying and appraising platinum, palladium, white golds both high grade and low, and other white alloys. The reason should now be clear—so few people are familiar with these tests, and there is so much neglected value on the market. FACTORY WASTES, FILINGS, SWEEPS

When a jeweler makes a piece of jewelry, he starts with a sheet of metal and he hammers it and drills holes in it, and files off the rough edges; possibly he engraves it. He winds up with a piece of jewelry that weighs one-half or maybe only one-tenth as much as the original sheet. The rest is now in the form of scrap, filings, and minute particles such as those that are swept up from the factory floor, all contaminated with more or less dirt. The large and relatively clean pieces he will wash and melt up for immediate re-use. The smaller scraps and filings have various kinds and amounts of trash mixed with them—steel from the files, emery from the emery cloth, tobacco, binding wire, bits of paper, possibly shellac from the stone-setter's bench, and what-not. The refining of such materials is part of the routine of most jewelry factories; the paper and other organic matter is burned out, steel

is removed with a magnet, nitric acid will dissolve out other base metals, and so on, the exact procedure depending upon the character and proportion of the trash and impurities. If his filings contain both gold and platinum metals, he will wish to separate these chemically and recover them in pure form. This calls for some additional procedures, all well within the facilities of most jewelry shops. Some of the original precious metal will, however, be in even smaller particles, admixed with a larger proportion of dirt. Thus it is the custom in jewelry shops to save carefully the sweepings from the floor, to filter the water in which the men wash their hands, to burn the polishing cloths and save the ashes,—all because these wastes contain enough precious metal to justify these efforts. The refining of this third group of wastes, this low-grade group, is a much more difficult matter. While it is shop routine to refine the high and medium grades, only the exceptional plant should attempt to refine low-grade wastes. The custom is to burn and sieve them, perhaps to subject them to other treatments, then for their ultimate refining to sell them to a professional refiner who can give them proper large scale treatment. The scrap and grindings brushed from the work-table of the dental mechanic have many of the characteristics of jewelers' wastes, and are treated in the same general manner. Jewelers, platers and others all have occasion to dissolve precious metals in acids or other solvents, producing solutions of varying composition and value. Sometimes the owner recovers the dissolved metal himself; sometimes he must sell it to a professional refiner. There are several other industries—photography for one—that generate precious metal wastes, and mostly they are of such a nature that their refining, as in the case of the jeweler's sweeps, is best carried out on a large scale. Here, then, is another field of activity for the buyer of old metals. He can act as a refiner's agent in purchasing such factory wastes as the owners cannot or will not refine at their own plants. And perhaps he can complete the industrial cycle by selling the refined metals back to the jeweler, dentist, or other worker. It should be clear that co-operation and understanding between the gold buyer and the refiner, as well as between the several other

segments of the precious metal industries, can work to the advantage of all concerned. The fostering of such understanding is one of the purposes of these chapters. (Methods used by jewelers, professional refiners, and others in the recovery of pure precious metals from the various kinds of scrap, filings, solutions, sweeps, and the like, are described fully in the book Refining Precious Metal Wastes, by C. M. Hoke, published by the Metallurgical Publishing Co., 123 William Street, New York.) THE PROFESSIONAL REFINER

The refiner has, as we have seen, several important functions in the economy of the precious metals. In some parts of the country the bulk of his work is the refining of ores and concentrates shipped to him directly from the mines. All refineries have facilities for sampling and assaying the materials that come to them. In other parts of the country the most plentiful material is "secondary" metal—scrap jewelry, old dentures, factory wastes, residues from electroplating or engraving, and such like. These various materials call for varying treatment, and the precious metals are separated out and purified by a variety of chemical and metallurgical processes, depending upon the metals present, the impurities involved, and the proportions in which they occur. As the last stage in his procedure, the refiner usually converts some or all of his pure metals into alloys—18-k gold, 14-k gold, sterling silver, iridio-platinum, rolled gold, dental alloys of various formulas, and so on,—and shapes them into wire, sheet, tubing, or such other forms as are desired by the trades and arts. LINKS IN OUR ECONOMY

It should be clear by now that the buying and refining of old precious metals are important links in the chain of our economy. They return to usefulness thousands of ounces of indispensable materials that might otherwise be lost to humanity. Gold is more than a trinket; for one thing it is a metallurgical necessity in dental surgery. Platinum is more than an item of luxury; it is an irreplaceable element in dozens of scientific applications of supreme importance. Nor has Nature been generous in supplying us with

these metals; they are scarce and hard to find. Accordingly the community owes respect and honor to the men who collect these metals—sometimes in forms that suggest neither beauty nor usefulness—and return them to the refinery, whence they will emerge to begin again the cycle of beauty and usefulness.

CHAPTER VI

Some Paragraphs for the Prospector Sooner or later any person—jeweler, refiner or gold buyer—who can appraise old metals will be asked to appraise minerals and ores. Nuggets that look like gold, and grains that might possibly be native platinum, will be brought hopefully to his desk. But while it is true that gold is gold wherever you find it, the fact remains that the identification and appraisal of ores call for different techniques from those described herein. While the tests and reactions can be adapted for use with ores, the adaptation may be modified considerably by the materials with which the native metals are combined or admixed. A man who is skilled in one type of appraisal may find himself at a loss in the other type. Such readers, therefore, as are interested in prospecting, are urged to study the excellent literature of this field, and to avail themselves of the help of our federal and state governments. A person who has already had experience in the tests described in this book will quickly pick up the additional techniques. SOURCES OF INFORMATION

Practically every state in the Union maintains a bureau that publishes authoritative information of interest to prospectors, miners, and others concerned with the development of our mineral resources and industries. These bulletins usually are distributed free of charge to residents of the state, and at cost to nonresidents. For example, Field Tests for the Common Metals, by George R. Fansett, is only one of the many useful publications of the Arizona Bureau of Mines. It gives tests for over thirty minerals, including gold and silver (but not platinum), and may be obtained from the University of Arizona at Tucson. The price is twenty cents. Most states also maintain laboratories for the identification of minerals, and will reply to questions regarding probable markets.

This service is often supplied free if the specimens originate within the state; a small charge is made for samples submitted from outside the state. When assays, quantitative chemical analyses, spectrographic analyses, microscopic or thin sections are desired, they are furnished at rates established by law. Many schools and universities, especially in regions with important mineral industries, give instruction in mining engineering and related subjects. For example, the University of California at Berkeley gives a correspondence course in mineralogy, and supplies each student with specimens of ore for study and comparison. The United States Bureau of Mines, although it does not duplicate the services rendered by state bureaus, is also glad to give advice on prospective markets and otherwise to assist in bringing together the buyers and sellers of mineral products. In addition it has published much authoritative and intensely practical information of a general character, for example its Information Circular 6148-R, entitled Selected Bibliography of Minerals and Their Identification. This pamphlet was prepared in answer to the many inquiries for the names of elementary books on geology, mineralogy, methods of identification, prospecting, and so on. It gives short notes on the character of each book, the number of pages, and the price. M. W. von Bernewitz' Handbook for Prospectors is written for the man in the field. It discusses grubstaking; the clothing and equipment needed; laws pertaining to mining; geology in prospecting; occurrence of ores; what minerals to look for and where; sampling; field tests and measurements; developing a prospect; markets and prices; and so on. It devotes almost two hundred pages to the occurrence, description, detection and uses of the metallic and non-metallic minerals, and it concludes with a glossary of terms used in mining. It is published by the McGraw-Hill Book Company, Inc., of New York and London. It is only one of the many helpful publications mentioned in Bureau of Mines Information Circular 6148-R. IT IS EASY TO RECOGNIZE GOLD

The student who avails himself of the above sources of information will learn that some tests are easy and sure. Thus native gold

is easily recognized because of its color, its heaviness, its high melting point, its malleability, and certain chemical reactions with which the reader is now familiar. These facts, and descriptions of the minerals that are sometimes confused with gold, as well as many other pertinent facts, are given in the literature, much of which is in popular form and suitable for the man in the field. PLATINUM NOT ALWAYS EASY

There is less popular information on native platinum-group metals. They are even rarer than gold, and found in fewer parts of the world, and while in some forms they are easily recognized, other forms are difficult to identify and even more difficult to appraise. Thus crude platinum in the form of easily recognized metallic grains is sometimes recovered from stream beds. In the field we take advantage of platinum's high specific gravity and pan the sample. When an experienced man is handling the pan, the platinum will hang back of the gold particles with which it is often associated. The platinum grains are often of a silvery white color that could be confused only with silver, or perhaps with bits of steel, from which the reader of this book could at once distinguish them by tests described herein. The presence of platinum should be confirmed by the ammonium chloride reaction given in Section C of Chapter IV. A hand lens will be an aid in examining these heavy particles and will indicate to an experienced eye whether it is worth while to send the sample to an assayer. The assay of the platinum-group metals is much more difficult than that of gold. Several scientific organizations, notably our National Bureau of Standards, have done much to dispel the mystery that once surrounded these metals, but even so, many chemists still approach without pleasure the tedious task of determining and separating them. On the other hand, the platinum metals are often found as minor constituents of ores of other metals, and in such small proportions that it is impossible to detect them in field tests. For example, let us consider one large source of palladium and platinum —the nickel-copper ores of the Sudbury District in Canada. The platinum content of these ores is little more than one part in two million. (Small amounts of rhodium and the other platinum

metals are also present, beside gold and silver.) Since large tonnages of ore, over 1,800,000 tons in 1934, are treated for the recovery of the main products, generous amounts of the platinum metals are obtained as by-products. In the treatment of these coppernickel ores, the platinum metals become concentrated in the copper-nickel matte of the smelting process, then when the nickel is electrolytically refined the platinum, palladium, rhodium, gold, silver and other metals are recovered as by-products. In 1938, 57 percent of the world production of platinum-group metals was obtained as by-products of the refining of ores in which some other metal—copper, nickel, gold, silver—was the main enterprise. Here, then, are ores of great commercial importance, but of so small a platinum content that the tests used on old jewelry will not reveal their value. What the prospector needs here is a knowledge of practical geology and mineralogy, to be confirmed by a laboratory analysis or assay. "BLACK SANDS"

Another source of platinum that has been the subject of much talk is the so-called black sands that often accompany gold in alluvial deposits. These sands are a mixture of heavy grains of various minerals, including magnetite, chromite, ilmenite, cassiterite, tourmaline and others, some of which are quite worthless. Occasionally the platinum grains are fairly easy to identify. The United States Bureau of Mines in its Information Circular I C 7000, dated March 1938, warns the public not to be too enthusiastic over the chances of striking it rich, and explains that for over half a century much money, energy and time have been wasted on black sands that generally were not worth the effort, partly because the total platinum content was low, partly because the stuff with which it was mixed was of a nature to make refining difficult and expensive. Circular I C 7000 describes the occurrence of these sands, machinery for grinding and concentrating them, and suggestions for marketing such sands as may really be of value. The metals in these sands dissolve very slowly in aqua regia; time, heat, and patience are required. This should be remembered whenever tests such as the ammonium chloride reaction, described in Section C of Chapter IV, are used to identify them.

SOME WORDS OF WARNING

Metals as valuable as those of the platinum group are bound to inspire dishonest men to dishonest deeds. Much money has been lost by the public to fraudulent stock promotions involving socalled platinum mines that contained no platinum at all. The reader should recall that most of our forty-eight states maintain laboratories for the identification and assay of ores and minerals, as well as bureaus that supply information on the marketing of such materials. These bureaus are at the command of any resident with legitimate need for their services, the prospective investor as well as the mining prospector, and there is no need to go far from home for information. By the same token, the jeweler or old-gold buyer in Boston or Baltimore, for example, who receives a sackful of what looks like gold nuggets from some stranger in a far-off mining town will do well to be curious. He may learn that the stranger is merely one who fears to entrust his secret to any home town neighbor. Or perhaps he is a crank who has canvassed every testing laboratory in his own region and will not believe what they tell him. Or the situation may have a sinister aspect, for sometimes the stranger is a promotor angling for a statement, on the stationery of a reputable firm, that his sample contains gold, the whole thing being merely a stock-selling scheme. ONE MORE LINK

On the other hand, a jeweler doing business in a mining region may find it important to be able to handle mineral specimens. If his neighbors trust his skill and integrity they will come to him in spite of the services offered by the government bureaus. And if he studies the available literature, and practises with samples of knowns and unknowns, he will soon find himself with a useful and profitable accomplishment—one with which he can forge one more link in the chain of our precious metal economy.

APPENDIX A. A LIST OF EQUIPMENT The following chemicals and equipment are mentioned in Chapters I, II and IV. Not all readers will want all items. Nitric acid. Touchstone. Hydrochloric acid. Acid bottles. Table salt. Standard yellow gold needles. Medicine droppers. File. Magnet. Samples of gold and other yellow metals of known composition. Standard needles of green gold and white gold. Samples of silver alloys of known composition. Samples of white base metals. Air-gas or oxygen-gas torch or blow-pipe. Potassium dichromate. Small glass rods. Sulphuric acid. Ferric chloride. Samples of platinum metals, gold, assorted alloys. Standard platinum testing needles. Spot plate. Dropping bottles. Small test tubes. Stannous chloride. Pure tin. Dimethyl glyoxime. Ammonia. Sodium thiosulphate—called "hypo." Tincture of iodine. Ferrous sulphate. Ammonium chloride or potassium chloride. The chemicals are all common and inexpensive, and can be found in most drug-stores and camera shops, or in any chemical supply house. Not all readers will want all items. The touchstone, acid bottles, and standard testing needles are sold by jewelers' supply houses. The only articles in this list that might be unfamiliar are the spot plate and the dropping bottles. These are described as follows in the catalogue of Eimer & Amend, dealers in laboratory

supplies, 633 Greenwich Street, New York, N. Y. Other dealers have access to this catalogue and can obtain similar articles. Dropping bottles: Eimer & Amend catalogue number 3-000. Two sizes, 30 cc. or 60 cc. Spot plate with cavities: Eimer & Amend catalogue number *3-745-5The standard platinum testing needles are sold by Sigmund Cohn, 44 Gold Street, New York, N. Y. B. WHEN HANDLING STRONG ACIDS

Nitric acid, hydrochloric acid and sulphuric acid must be handled with care. They quickly attack the skin, clothing, wood and metal surfaces, and so on. When working with them, be sure to have close by plenty of water in which to wash your hands—running water or a big basin. Provide yourself with old rags for wiping spilled acid from the table or floor, and burn them after use.

If you spill acid on your hands or clothing, the first thing to do is to wash it off immediately, using plenty of plain water. After that it does no harm to neutralize with a little weak ammonia or

bicarbonate of soda. Never attempt to neutralize until after you have removed all acid possible with plain water.

c. How To DETERMINE SPECIFIC GRAVITY

It takes only a few minutes to determine specific gravity, and the equipment is simple—a good balance with weights; a piece of thin thread; a cup of water and a support to hold it. Method: First weigh the article as usual, writing down the weight. Next, weigh it while it is hanging in water; the weight will be slightly less. Subtract the second weight from the first. The specific gravity will be the first weight divided by this difference. To explain: Most balances have a hook at the end of the beam where the pan is hung; hang your object on this hook, using thin silk thread. Weigh the object, and call this weight Wa. Now fill a small cup with water, and bring it up under the hanging object until the latter is completely immersed. Many balances are accompanied by a support for this purpose—it is shaped like an inverted U, just large enough to bestride the pan. You can make such a support by bending a piece of sheet metal or cardboard. Next, weigh the object while it hangs in the water. Call this weight Ww. Find the difference between Wa and Ww and call it D.

Be sure to get rid of bubbles of air that may attach themselves to your article; they will upset the reading. This method applies to objects heavier than water. The table gives the specific gravities of pure metals only, and alloys will be different; for example the figure for 18-k green gold is about 15.8, more or less, depending upon the formula. 18-k yellow gold, about 15.1. 14-k yellow gold, about 13.2. 10-k yellow gold, about 11.7. Sterling silver, about 10.4. Coin silver, 10.35.

This table shows the reactions of the commoner metals and their alloys to cold, full-strength nitric acid; to cold full-strength hydrochloric acid; and to the oxygen-gas flame. It is assumed that the samples will be in the form of small articles—neither as a finelydivided powder nor a large mass. Specific gravities are given in the usual units—water = 1.0—and melting points are expressed in degrees Centigrade. The small raised numerals refer to the following notes: 1. Iron, steel and chromium under concentrated nitric acid often remain "passive" or insoluble for some time. But if scratched, or touched with a wire of some dissimilar metal, they will begin to react with vigor. 2. Lead is readily soluble in warm nitric acid, especially if the latter is diluted. It dissolves slowly in hot hydrochloric acid, but on cooling the white insoluble lead chloride precipitates out. 3. Silver when treated with hot hydrochloric acid, or hot aqua regia, is slowly converted into the white insoluble silver chloride. 4. Tin is converted by nitric acid into a white gelatinous solid called meta-stannic acid. It dissolves promptly in hot hydrochloric acid; slowly in cold.

E. SOME DEFINITIONS AND FORMULAS alloy. (1) A mixture, or combination, or solid solution, of two or more metals, usually made by melting them together; as, brass is an alloy of copper and zinc. (2) The baser metal, or metals, combined with a finer one. aluminum bronze. Alloy of copper and aluminum, having a color resembling gold. amalgam. Alloy in which one component is mercury. argent. French word for silver. argentan. French word for nickel-silver. Britannia metal. White alloy, originally made in England, containing tin, antimony, and some copper. Harder than pewter. bronze. Alloy whose principal components are copper and tin. cadmium. White metal, often added to solders to lower the melting point and make them flow more easily. carat. A unit of weight for gem stones. Not to be confused with karat, a term denoting the ratio of fine gold in an alloy. The word probably comes from the Greek her at ion, a seed that was used in ancient times as a unit of weight. Its value has varied from time to time. The metric carat is the standard now commonly used, equivalent to 200 milligrams, or 3.08647 grains Troy. coin gold. U. S. A., 90 percent gold, 10 percent copper. Great Britain, 91.66 percent gold, 8.33 percent copper. cuivre. French word for copper. dwt. Abbreviation for pennyweight. electrum. (1) A native gold alloy, containing considerable silver. (2) Nickel-silver. E.P.N.S. Abbreviation for "electro-plate on nickel-silver." E.P.W.M. Abbreviation for "electro-plate on white metal." fine. As applied to gold or silver, pure. Thus fine gold is pure 100 percent gold, without alloy. hard platinum. Pure platinum hardened by the addition of (usually) about 10 percent iridium; used in jewelry and other applications where strength and resistance to abrasion are required. Other hardeners are sometimes used, 5 percent ruthenium being one of the best.

invar. Alloy of 36 percent nickel and 64 percent iron, used in horology because of its very low coefficient of expansion. karat. A twenty-fourth part; a term used to express the ratio of fine gold in an alloy. Thus, pure gold is 24 karats fine; see page 12 for further examples. Should not be confused with carat, a unit of weight used for gem stones. Both words are probably derived from the same Greek word, keration, meaning a seed used as a unit of weight. In the U. S. A. the form karat is used for the ratio of gold in an alloy, while carat denotes the unit of weight for precious stones. Outside the U. S. A. the form carat, as well as other spellings, is used for both meanings. lernel. Filings swept from a jeweler's workbench. They contain particles of precious metal mixed with dust, bits of solder, steel from the tools, and so on. From the French limaille, meaning filings. monel metal. An alloy containing about 65 percent nickel, 30 percent copper, and small amounts of iron and other metals. muriatic acid. Another name for hydrochloric acid. noble metals. Metals that are permanent in air, showing no oxidation under ordinary conditions. The Alchemists applied the term to gold and silver, which they believed to possess special virtues. The six metals of the platinum group have now been added to this category. oreide. Copper alloy of a golden color, containing some zinc and possibly a little tin. osmiridium. Naturally occurring alloy of osmium and iridium. The hard grains are used for tipping penpoints. Also called iridosmine. pewter. Alloy formerly popular for household and table ware. Consists largely of tin, with copper and lead in varying proportions, with or without small amounts of zinc, antimony, and bismuth. pinchbeck. Alloy of about 88 percent copper and 12 percent zinc, having a reddish golden color. Used in cheap jewelry, etc. pink gold. Gold alloy containing a fairly high proportion of copper, plus a little nickel, with or without zinc and silver. precious metals. Metals which are prized because of physical and chemical properties that make them desirable for coinage or

INDEX ACID bottles, 12 Acids, when handling, 84 Alkaline solutions, 60 Ammonium chloride test, 59 Antiques, 36 Aqua regia, 14, 47 and gold, 14 and silver, 21 and stainless steel, 25 and platinum metals, 46 Archimedes, 61 Assay Offices, 69 Assaying, 8, 72 BASE metals, 12,18, 24, 26,43, 86 and stannous chloride, 51 "Black sands," 81 Blow-pipe, oxy-gas, 44 Bottles, acid, 12 dropping, 45, 47, 84 CHAINS, 35 Chromium, 26, 27, 86 Coin silver, 23 Commercial standards, 31, 33 Contact points, 27 DENSITY, 20, 61, 85 Dental alloys, 16, 37, 73 Dichromate test, 22, 25 Dimethyl glyoxime solution, 53 Dropping bottles, 45, 47, 84 ELECTROGRAPHIC tests, 60 Enforcement of laws, 34 Equipment for testing, 11, 45, 83 FACTORY wastes, 74 Fansett, George R., 78 Ferrous sulphate test, 58 Field tests, 78 File, 11, 35 Filings, 74 Flame test, 19, 26, 27, 43, 86 Fraud, 36, 66 GERMAN silver, 25 Gilchrist, Raleigh, 57 Glow test, 58

Gold and aqua regia, 14 and ferrous sulphate, 58 and the flame, 20 and nitric acid, 12 and stannous chloride, 50 buying and selling, 63, 66, 71 rilled, 22, 25, 36, 71 green, 15, 21 native, 7g "on sterling," 22 plated goods, 71 price of, 70 red, 16 rolled, 22, 25, 36, 71 white, 16, 28, 39, 40, 42 yellow, 11, 13 Guilds, 29 HALL marks, 29 Hydrochloric acid, 14, 25, 27, 84, 86 IODINE test, 58 Iridium and iridio-platinum, 39, 40, 56, 57> 73 "JEWELRY palladium," 41 KARAT, 12 to determine, 13 stamp, 29, 31 LAWS, stamping, 30, 32 Lea, Carey, 57 Licensing of gold handlers, 68 Lydians, 7 MAGNET, 18, 43 Melting points, 86 Minerals, to identify, 78 Mints, 67 Molybdenum, 19, 26 NEEDLES for testing, 11,13, 15,42, 84 Nickel, 16, 19 and dimethyl glyoxime, 54 Nickel-silver, 25 Nitric acid, 12, 84, 86 and gold, 12 and silver, 20, 21 and stainless steel, 19, 25 and platinum metals, 26, 28, 46

OLD-GOLD industry, 65, 70, 74 Ores, to appraise, 78 Osmium, 39 Oxygen-gas flame, 19, 26, 27, 43, 86 PALLADIUM, 16, 19, 28, 39, 41, 44, 86 and dimethyl glyoxime, 54 and the flame, 19, 44, 86 and iodine, 58 and nitric acid, 28, 46 and stannous chloride, 50 in jewelry, 41, 46 in ores, 80 Platinum, 28, 39, 40, 86 and ammonium chloride, 59 and the flame, 19, 43, 86 and iodine, 58 and nitric acid, 28, 46 and stannous chloride, 49, 54 buying and selling, 69, 72 group of metals, 39 native, 80 stamping laws, 32 Precautions, 35, 82 Prospectors and prospecting, 78 QUALITY stamps, 29 REFINER, the professional, 67, 75, 76 Refining precious metal wastes, 60, 75, 76 Regulations, Government, 67 Resistance alloys, 26 Rhodium, 28, 39, 41, 46 Ruthenium and its alloys, 39, 41, 46, 57 Ruthenio-platinum and iridio-platinum, to distinguish between, 57 SCIENTIFIC apparatus, 37, 72 Silver, alloys of, 23 and aqua regia, 21 and dichromate, 22

and the flame, 19 and nitric acid, 21 brazing alloys, 24 buying and selling, 69 chloride, 21 plated goods, 22, 70 reactions of, 20, 86 solders, 24 sterling, 22, 23, 32 Solder, allowance for, 31 Solutions, alkaline, 60 old, 59 standard, 49 Specific gravity, 20, 61, 85, 86 Spot plate, 45, 84 "Spread" in prices, 70, 75 Stamp of quality, 29 Standard needles, 11, 13, 15, 42, 84 Standards of quality, 30, 33, 34 Stannous chloride solution, 48 Steel, stainless, 19, 25 Sulphuric acid, 26, 27, 84 Sweeps, 74 TANTALUM, 19, 20, 26 "Testing Solution A," 48 "Tolerance," 31 Touchstone, 7, 11, 13 Trademarks, 30, 31, 35 Troy weights, 64 Tungsten, 19, 26 U. S. A. as gold buyer, 66 U. S. Government Regulations, 67 U. S. Bureau of Mines, 79 U. S. Bureau of Standards, 32 VIGILANCE Committee, 34 Von Bernewitz, M. W., 79 WARS, effects of, 40 Wastes, factory, 74 Weighing, 63