theory and practice derived from former professional experience, and further showed, what is not always the case with chemists, a capacity to apply his knowledge in the larger way required for commercial results." There was delay at first in disposing of the gold that came to the Mint, and some impatience on the part of consignors, but the capacity of the Mint was soon enlarged to meet promptly every demand. In the course of five years the pressure of gold at the Philadelphia office was relieved by the creation of a Government Assay Office in New York and a Branch Mint at San Francisco. Then came a change in the standard of silver coin, causing an immense recoinage in small pieces; and then the issue, in place of the old copper cents, of copper-nickel pieces, and, after these, of bronze; each calling for other processes of assay and involving additional work.
An improved process for refining gold was described by Prof. Booth, in a letter to the Wastage Commission, as follows: "I refine usually to 993 and 995 m., and sometimes, to make a finer gold, I heat the alloy of gold and silver with parting acid, so as to nearly separate them, and then heat the residue with oil of vitriol and saltpeter, at a steam-heat, by which I have brought the gold to 998 m. The process is my own, and not known outside of the Mint." A paragraph from an article in the Journal of the American Chemical Society for June, 1885, on The Smelting Furnace of the United States Mint, is quoted by Mr. Dubois as characteristic. "My last improvement," Prof. Booth says, "which is still practiced, consists in the very simple operation of melting all the iron residues from the furnaces, even including grate-bars, and keeping them in a quiet melted state, so as to allow the heavier gold and silver to settle out of the iron. When the mass is cold, the precious metal is knocked off the bottom by a hammer as a single tough king, with scarcely a trace of iron in it, while the iron mass above it has never yielded a trace of gold or silver to the assayer. Instead of spending three weeks of annual vacation from melting in hammering tons of accumulated iron, we now melt through the year, whenever convenient, from five to fifty pounds of iron residues at a time. We gathered in one melting, last autumn, a cake of a few ounces of gold and silver from a mass of over fifty pounds of iron in a part of a day, and the latter was entirely free from the precious metals. When I first succeeded with this process, I could hardly believe in the perfect separation from iron, and the late Mr. J. R. Eckfeldt, the best assayer in the United States, doubted it, until, by numerous tests made from a piece of some thirty pounds of iron, he found a total absence of gold and silver."
The difficulties met at the Mint in adapting processes to the various kinds of metallic impurity that came in with the gold
