120 THE POPULAR SCIENCE MONTHLY, 



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 ofBce 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 re- 

 fine 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 out- 

 side 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 



