SOLUBILITY OF GOLD, 433 



cold ones. Marcasite is more easily soluble than pyrite, and the simple 

 precipitated sulphide goes into solution most readily of all. I tliink there 

 can be no doubt that pyrito and marcasite form double salts with sodium 

 sulphide entirely analogous to the soluble compounds of mercuric sulphide. 

 Marcasite is more easily attacked than pyrite, just as metaciiniabarite is 

 more susceptible to the action of reagents than is cinnabar. 



Solubility of gold. — The association of gold and pyrite is world-wide. Ac- 

 cording to Claim ^ there is no jiyrite wliicli does not yield traces of gold 

 when carefully tested. This, indeed, does not accord with my experience, 

 for extremely careful tests of some pyrite in my laboratory have failed to 

 reveal any indication of gold. Gold is associated with quiclvsilver, however, 

 at Steamboat Springs, at some points on the gold belt of California, at the 

 Manzanita mine, at the Eedington mine, and some other localities. From 

 these fiicts I concluded that gold should be soluble in sodic sulphide. On 

 warming chemically pure precipitated gold dust with a solution of sodic 

 sulphide the glittering scales of gold gradually disappeared. The filtrate 

 after a proper manipulation yielded a purple precipitate with phosphorous 

 acid.- 



A solution containing 843 parts of sodic sulphide (Na'S) by weight 

 dissolves one part of gold at the ordinary temperature of the atmosphere. 

 Gold also dissolves in sodic sulphydrate and in solutions of sodic carbonate 

 partially saturated with sulpliydric acid at ordinary temperatures. The 

 solubility appears to be increased and facilitated by heat. 



Solubility of cus. — Cupric sulphide dissolves less readily than pyrite. Ex- 

 periments were made by keeping CuS in contact with the solvents in bottles 

 at about 20° C. for two weeks, the bottles being shaken from time to time. 

 A little less than five tiiousand parts by weight of sodic sulphydrate are 

 required to dissolve one part of copper sulphide. About eight thousand 



' BisclioPs Cbom. und phys. Geol., vol. 3, 1866, p. 939. 



"Bischof !oug since remarked that, were tbe existence of sulphide of gold in nature proved, the 

 possibility of double sulphides of this metal, such as can be artificially produced, and of their depo.si- 

 tion from aqueous solutions would be ascertained (ibid., p. 838). So, also, Prof. T. Egleston has found 

 that gold kept iu contact v.ith alkaline sulphides produced solutions giving reactions for gold (Trans. 

 Am. Inst. Min. Eng., vol. 9, 1881, p. 640). lie did not show, however, how such sulphides or their 

 equivalents could form or exist in nature, and seems to conclude that the compound existing iu natural 

 solutions is the chloride. 



MON XIIT 28 



