SECONDARY PRECIPITATION OF GOLD 253 
native mercury, arsenic, and antimony can act in a similar way. 
There is, however, little geological evidence of such precipitation, 
though it is conceivable that electrum may sometimes be formed 
in this way. Ransome’ mentions the association of wire gold 
with native silver in the Breckenridge district, and here the silver 
may have been the precipitating agent. The other metals having 
a higher electrolytic solution tension than gold and occurring free 
in nature are not common in gold deposits, and no record of their 
having caused precipitation of gold is found. Tellurium, usually 
classed as a non-metal, may interact with gold chloride in solution 
to precipitate gold, as shown by the following equation? 
3Te+4AuCl,=4Au+3TeCl, 
This may account, in part, for the precipitation of gold in the 
oxidized portion of gold telluride deposits. 
it: SULPHIDES, TELLURIDES,. ETC. 
a) Simple sulphides.—That sulphides are capable of precipitat- 
ing gold has been known for many years. In 1866 Wilkinson 
showed that metallic gold is precipitated by the sulphides of copper, 
iron, arsenic, lead, zinc, molybdenum and tungsten, and to this 
list Skey* added the sulphides of tin, bismuth, platinum and gold. 
These investigators showed that the precipitates obtained were 
metallic gold, not gold sulphide, though the latter would be the 
compound naturally expected by some such reaction as follows: 
2AuCl,+3ZnS = Au.S,;+ 3ZnCl, 
It is of interest to consider the possible reasons for the precipitation 
of the metal instead of the sulphide. 
Hydrogen sulphide, under ordinary conditions of temperature 
and pressure in the laboratory, reacts with gold salts in solution 
to form Au.S,,5 a stable sulphide of extremely low solubility, as 
follows: 
8AuCl,+9H.S+4H.0 = 4Au.S.+ 24HCI+H.SO, 
tF. L. Ransome, U.S. Geol. Survey, Professional Paper No. 75, p. 82. 
2V. Lenher, Jour. Am. Chem. Soc., XXIV, 355 (1902). 
3 Trans. Roy. Soc., N.S.W., VIII, 11 (1866). 
4Chem. News, XXIII, 232; see J. B. u. d. Fortschritte d. Ch., 1871, p. 344. 
5 Gmelin-Kraut, V, P. II, p. 268. 
