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which is boiled by placing the vial in a bed of hot sand. Bright red fumes soon arise, showing that the action of the acid upon the silver has begun. In about ten minutes the acid is poured off, and a quantity of less dilution is poured in to dissolve out the last traces of the silver. The silver and nitric acid uniting have formed nitrate of silver; and the remainder of the cornet is pure gold. It is a fragile roll, looking very like the brown tinder left in burning writing paper. This is taken out, washed in distilled water, and melted in a crucible, when it at once resumes its metallic appearance. It is carefully weighed in the operator's delicate scales, the result showing the fineness of the bullion; or how large a

portion of it was gold, and how large alloy. The value of an ounce of any fineness being already known, the whole value of the gold in our deposit is readily ascertained.

There was, moreover, some silver contained in our deposit—a small proportion probably, but still of some value—and for this we are to be paid. To ascertain this another half gramme is cut from the assay-slip, but no silver is added tp it. It is cupelled to extract the base metals, and being weighed with the cornet of puro gold, the excess in weight shows how much silver there was.

We have spoken of only a single assay; but in fact two are taken from each deposit, by different assistant-assayers. If these agree, they are deemed to be correct. If they differ, a new assay is made by each. If they still differ, it indicates that, in melting, the deposit was not thoroughly mixed, and that one portion of the bar was richer than another. In that case it is re-melted, and the process is gone over again. The process of assaying is a very delicate one, demanding great practical skill, since an error of the hundred-thousandth part of an ounce in the small pieco assayed would make a sensible difference when multiplied by the quantity of a large deposit. But such is the acknowledged skill of our nssayers, that Dr. Torrey's mark on a bar is never questioned.

To indicate t he fineness of gold, we adopt the simple French decimal system. The bullion is supposed to be divided into 1000 parts. If it is pure gold, its fineness is }888 , tnat isi ^ it contains 100 parts alloy, its fineness is rffift; or, in decimals, -900, and so on. The English

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ASSAY WEIGU-BOOM.

mint has used a less scientific system. It supposes the bullion to be divided into 24 parts, called carats. If it is pure, it is said to be 24 carats fine. If it contains 2 parts out of 24 of alloy, it is 22 carats fine; and so on. Recently, however, the assayers have been required to make their reports also in decimals; and this system will probably in time wholly supersede the old one.

The Assayer fills out a report stating the fineness of the gold, and the amount of silver contained in it. This is sent to the office of the Treasurer, where the necessary caleulations are made, and a memorandum is sent to the office of the Superintendent for verification. This memorandum is made out in tabular form, printed in crimson, and signed by the Chief Clerk, in behalf of the Treasurer. The memorandum for our deposit reads as follows:

No. 1912—Memorandum of Gold Bullion deposited in the United States Assay Office, at New York, the 11th day of Jimc, 1861, by John Smith.

Description, California Grain.— Weigut, before melting, 1120-07 ounces; after melting, 1120-34 ounces Fineness, -923.— Value of the Gold, $21,376 20.— Value Of Silver parted from the Gold, $94 40.—Deductions for Parting, Coinage, and Fine Bars, $162 90—Net Value $21,307 70.

I certify that the net amount of the above deposit is Twenty-one thousand three hundred and seven.^Lfe Dollars, payable at the U. S. Assay-l rlQ Gold Coini,

Office, only on presentation of the I . I 1*1,111 M. Receipt, of a corresponding date [ 1 In silver Coln«. and number, heretofore issued. J ;''

Our deposit, being of California gold, was quite pure. It lost less than half an ounce in melting, and being -923 fine, contained only 77 parts in a thousand of alloy, including the silver. It was, in fact, worth more than its weight in gold coin, of which our standard is -900; that of British coin being 22 carats, equal to about -916. If our deposit had been in foreign coin, with no counterfeits in it, about one-tenth part would have been alloy; if it had been jewelry or plate, probably it would have contained quite half alloy. As we chose to take our pay in coin, the cost of coinage is charged to us. The deduction would have been less if we had taken fine bars, as is usually done when the gold is wanted for exportation or deposit. The charges are made according to a fixed scale; varying for parting and refining with the character of the deposit; for fine bars it is 6 cents, and for coinage 50 cents, per hundred dollars. In four or five days after making our deposit it is assayed, its value ascertained, and we get our warrant for the payment in coin, for which, however, we must now wait a while. Formerly, when Uncle Sam was "flush," he used to keep a balance of a few millious in the hands of the Treasurer of the Assay Office, so that he could cash the Superintendent's warrants at once. But having met with some losses of late, and being subject to heavy expeuses, he finds this inconvenient. In fact, he is "short." So we must wait for our money until the bullion can be sent to Philadelphia and coined. This will take twenty or

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MELTEB AND EEFLNEU8 VAULT.

thirty days. But the hardship is not very great, as we can easily "make a raise," if need be, on our warrant.

Hitherto our deposit has been kept separate from all others. But now that its value has been ascertained, and we have a warrant for the payment, it is cousidered us the property of the United States; and in the processes of refining is mingled with other deposits, losing its personal identity.

The operation of refining, which Mr. Kent now commences, is a repetition on a large scale of the delicate processes of assaying. The bars are melted in a large crucible, twice their weight in silver being added. The molten mass is dipped up, and flung, with a peculiar jerk, into a cistern of cold water. We have all, for one purpose or another, poured melted lead into water, and noticed the minute fragments into which the metal is divided. The same thing happeus to the compound of gold and silver. It is divided into small portious, and looks not unlike a heap of shavings. This process is called "granulating," its object being the same as the rolling out of the assayslips, to allow every part of the metal to come in contact with the nitric acid, in which it is to be placed to extract the silver.

The water is drained off, and the granulated metal is taken to the "Parting Houses." — These are closets with sliding windows, which shut close in order to prevent the fumes from escaping. The bottom is a tank with steampipes around it. Here are placed large jars of poreelain, holding about twenty gallous. Into each is put 150 pounds of the metal. The nitric acid, which has been decanted from the carboys in which it is held, is poured in—about ten

gallous, properly diluted, to each jar. Mx or seven thousand carboys of acid, costing nine dollars each, are used in the course of a year. Great

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POUEINU OUT ACID.

care must be taken in handling it, for it will burn the flesh or clothes of the workmen should it touch them. It will not, however, act upon

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passing into the room,
escape through the tall
chimney seen in our
first illustration. This
vapor presents a brill-
iant appearance, and
many who see it sup-
pose that vast quanti-
ties of gold are passing
off into the air. The
vapor, however, is no-
thing more valuable
than nitrous acid. Aft-
er boiling for six hours,
the acid, or rather the
combination of nitric
acid and silver, which
is nitrate of silver, is
drawn off by a gold si-
phon, worth three thou-
sand dollars, and a
stronger dilution of acid
poured in. This is boil-
ed for another six hours,
when all the silver is
supposed to be taken
up; it is drawn off, as
before, and the gold is
left in the jar. The ni-
trate of silver is now in
the form of a dark fluid,
looking like a pale greenish ink
it again.

The gold, which is in the form of a dark brown powder, resembling Scotch snuff, with no lustre or indication of its metallic character, is yet almost pure—probably -993 fine. It has been by this process purified as high as -995. It still contaius a little nitrate of silver mixed with it, to remove which it is placed in a large tub, having at the bottom a strainer composed of layers of muslin and filtering paper. A stream of warm water is poured upon it, which

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CASTING VUtE BAES.

penetrates the mass, washing away the nitrate. In eight or ten hours it is thoroughly cleaused. It is then taken to a hydraulic press. About a peck is placed in a "stave" or mould. A pressure of two hundred tous is applied, which forees out the water through slits left in the stave, and compresses the powder into a solid cake, about twelve inches in diameter and three inches thick. The top and bottom of this cake present a dull yellow '' frosted" appearance; but the sides, which have been exposed to friction, shine with metallic lustre. It looks like a fine yellow cheese, by which name it is called. One of these gold "cheeses," however, weighs about sixty pounds, and is worth eighteen or nineteen thousand dollars. Twelve of them are made from tho contents of one filter

These cheeses, after having been baked in an oven, heated by steampipes, to expel any moisture that may remain, are taken down to the " Fine Melting - Room," broken up, and melted. A little saltpetre and borax is thrown into the crucible, to extract any base metal which may have become mixed. It is turned into iron moulds, smoked with rosin and pitch to prevent adherence; oil is poured on the bar while cooling, to give it a good surface. It comes out in the shape of " fine bars," each weighing about seventeen pounds, and worth some five thousand dollars. These are cooled in a "pickle" of sulphuric acid diluted with water, which removes any oxydation of iron on the surface, and gives them a bright appearance. These bars are about -993 fine.

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When the moulding is begun a cake of five or six ounces is cast, and one notch is cut in it as a mark; when the last bar is cast another cake is made, and marked with two notches. These are called "assay pieces;" they are stamped with the number of the melt, and assayed, as before explained. Each bar is then weighed separately by the Bar Wcigh-Clerk, who caleulates its value from the weight and fineness, as reported by the Assayer. The number of the melt, the year of melting, the office where refined, the number of the bar, its weight, fineness, and value, are then stamped on every bar. These are now delivered to the Treasurer, who keeps a record of every one. Thus the bullion, which was delivered to the Meltcr and Refiner in various shapes, is now converted into "fine bars," refined, assayed, its exact value stamped on each, and is ready to be sent to the Mint at Philadelphia for coinage, or to be exported. For shipments bars are generally used in preference to coin, because they are

more convenient to pack, and there is a saving of the expense of coinage.

It will be remembered that two parts of silver were melted with every part of gold. This, dissolved in nitric acid, constituting nitrate of silver, was left at the "Parting House." The recovery of this silver forms one of the most beautiful operations in the Assay Office.

This nitrate, in the form of a greenish fluid, is poured into an immense tank, holding about 3000 gallons, in which has been placed a strong solution of common salt. Salt is a combination of chlorine and soda—its chemical name is chloride of sodinm. Four substances are contained in this tank: silver, combined with nitric acid, forming nitrate of silver, and chlorine, combined with soda, forming chloride of sodinm. A double chemical action takes place. Nitric acid has a stronger affinity for soda than for silver, and chlorine a stronger affinity for silver than for soda. The consequence is that the acid leaves the silver and unites with the soda, forming nitrate of soda; while the chlorine unites with the silver, forming chloride of silver. The chloride of silver thus formed falls down, or is "precip

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