SOLUTION OF GOLD. 1091 



The conclusion that gold is soluble in ferric and cupric chlorides, in 

 acids where oxygen is liberated, and is possibly soluble in ferric sulphate, 

 and that these processes are promoted by increasing temperature, is of the 

 greatest importance in reference to the segregation of gold. It has been 

 pointed out that the ic salts are those which are extensively produced in 

 the belt of weathering by descending solutions. Iron sulphide is the most 

 abundant sulphide. By the reaction of oxygen upon it ferric sulphate is 

 produced, and by its decomposition sulphuric acid. Ferric chloride would 

 form wherever chlorine is present. If copper sulphides occur, these would 

 be transformed to similar salts. Thus in the belt of weathering considera- 

 ble quantities of the solvents of gold are formed. In connection with the 

 production of a large amount of these reagents where the solutions are 

 descending, the law of mass action leads to the conclusion that the gold 

 will be dissolved somewhat in proportion to the mass of these compounds 

 produced. Furthermore, where the solutions are descending there is a 

 rise in their temperature, and the work of Stokes shows that this further 

 increases their activity. Hence, under normal conditions in a region of 

 mineralization where there are sulphides and where gold exists, one would 

 expect that the dispersed descending solutions would dissolve gold in con- 

 siderable quantit}^. 



precipitation. — In whatever form gold is carried it is known to be pre- 

 cipitated in the first concentration as metallic gold or as a telluride. 

 Whether it is also precipitated as a sulphide is uncertain. 



It is easy to suggest various causes for the precipitation of metallic 

 gold from its solutions. First, it is well known that gold solutions are 

 immediately precipitated by the more basic metals. Of these metals there 

 is likely to occur underground those of copper, silver, and tellurium. Occa- 

 sionally also iron may occur. The rapid precipitation of gold from its 

 solutions by contact with iron, copper, and silver are well known. 



Recently Hall and Lenher have shown that tellurium completelv 

 precipitates gold from its solutions according- to the following- reactions :° 



4AuCl 3 +3Te=4Au+3TeCl 4 



They state: "Time is a considerable factor in bringing about complete 

 precipitation, from two to three hours being necessary with continued 



«Hall, R. T>., and Lenher, Victor, Action of tellurium and selenium on gold and silver salts: 

 Jour. Am. Chem. Soc, vol. 24, 1902, p. 919. 



