The next step is to l(cupel° the button, so as to obtain the gold and silver in a pure state. Cupellation is based upon the fact that when an alloy of gold, silver, lead, and base metals is heated in a current of air, the lead and the other base metals will oxidize, and the melted lead oxide (alitharges) will retain the other oxides in solution. Moreover, if the crucible in which the operation is carried out is porous, the melted lead oxide will soak into it, carry ing the base oxides with it, and leaving a button of pure gold and silver behind.
The in which this is performed is made of bone-ash, and after the button left from the scorification process has been heated in the cupel for a short time, the process indi cated above takes place, its completion being indicated, to the practiced eye, by play of ir idescent colors on the cupelled button. The button is finally allowed to cool, and after it has been taken from the cupel, any small parti cles of bone-ash that remain adhering to it are removed by a brush.
If the original ore contained no silver, the assay is now completed, and it only remains to weigh the gold button, and compare its weight with that of the sample of ore used in the assay. But if silver is present, one other process, known as must be carried out, in order to separate the gold from the silver. Parting depends upon the fact that nitric acid will dissolve the silver out of an alloy of silver and gold, provided the weight of silver present is at least 2.5 times as great as the weight of the gold. In order to ensure the fulfilment of this necessary condition, the button, as it comes from the cupel, is melted with 2.5 or 3 times its own weight of silver that is known to be free from gold, and the alloy so formed is flattened out into a thin plate or ribbon, which is then rolled up into a little spiral, or (cornet,* and boiled in nitric acid. The cornet is next washed in dis tilled water, and boiled again in nitric acid, to remove the last traces of silver; after which it is thrown into a crucible and melted into a but ton, for weighing. The button obtained by this final process consists of pure gold.
Assay Offices in the United States are gov ernment establishments in which citizens may deposit gold and silver bullion, receiving in re turn its value, less charges. The offices are in New York city; Boise City, Idaho; Helena, Mont.; Denver, Col.; Seattle, Wash.; San Francisco, Cal.; Charlotte, N. C.; and Saint Louis, Mo.; Carson City, Nev.; Deadwood, S. D.; New Orleans, La.; Philadelphia, Pa.
The assay office in New York was estab lished by law in 1853, and was opened in the autumn of 1854. The first assayer of the New York assay office was Dr. John Torrey of Co lumbia College, who was appointed in 1854 and held his position till 1873. On his death he was succeeded by his son, Herbert Gray Torrey. Andrew Mason, who was appointed superin tendent in 1883, having previously been assistant assayer and welter and refiner. While holding the latter office he substituted the use of sul phuric for nitric acid in the refining process, thus saving this one assay office $100,000 per annum.
The United States assay office is in a build ing located beside the more imposing sub treasury building, at the intersection of Wall and Broad streets, which marks one of the most historic spots in the country, namely, the site of the old Federal Hall, where Washing ton took the oath as first President of the United States. Although the building is small,
yet it only masks a really large, inner building surrounded on all sides by office buildings and the sub-treasury. The assay offices, and particu larly this one, have an important position in the world of finance, for here the precious met als — gold and silver — in all forms and con ditions of fineness are assayed and refined. In brief, the work of this office consists in assay ing or determining the value of gold and silver, in whatever form presented, as coin, jewelry, or in any other shape. Any one wishing to have gold or silver assayed in quantity or wishing to sell to the government may present his property at the assay office, where he may have the metal reduced and made into bars, or if he prefers, he may sell his bullion to the gov ernment. The charge for doing the work is merely nominal, and based on the actual cost. Millions of dollars are stored at all times in the vaults. When the metal is received, the first step consists in weighing the coin, bars, jewelry or tableware. This is done with great exact ness and a receipt is given. Each person's hold ings are placed in a box and are taken to the melting-room, where they are placed in cruci bles with a fltuc and smelted and cast in ingot molds, the pouring being a highly picturesque ti operaon. A small chip is taken from the bar for assay. See COINAGE.
If the depositor wishes to part with his bullion, the government pays for it at the pre vailing price and proceeds to separate or part the gold from the silver. The price of gold never varies, costing $20.67 a fine ounce. Sil ver fluctuates with the market.
The importance of the assay office in its rela tion to the financial world, the treasury, and the mint cannot be overestimated. During a recent year 10,739 melts of gold deposits and 1,642 melts of silver deposits were assayed. Fine gold melts numbered 324 and fine silver melts 49. The number of special assays was 850. The total assays was 71,000. Consult Bugbee, E. E., Text-book of Fire Assaying' (Boston 1915) ; Outerbridge, A. E., tAssaying by the Spectroscope' (Philadelphia 1874) ; Ricketts, P. de P., 'Assaying and Assay Schemes> (New York 1879) ; Smith, E. A., 'Sampling and Assay of Precious Metals' (London 1913) ; Furman, H. v F., 'Manual of Practical Assaying' (New York 1910) ; Smith, J. R., 'Modern Assaying' (Philadelphia 1910) ; Fulton, C. H., 'Manual of Fire Assaying' (New York 1911) ; Lon, A. H., 'Technical Methods of Ore Analysis' (New York 1911) ; Rhead, E. L., and Sexton, A. H., 'Assaying and Metallurgical Analysis for the Use of Students, Chemists and Assayers' (Lon don 1911) ; Park, J., 'Text-book of Practical Assaying> (London ; Wraight, E. A., 'Assaying in Theory and Practice' (New York 1916) ; 'Laws of the United States relating to the Annual Assay' (Washington 1880).