PRECIPITATION OF SULPHIDES. 1115 



ber of the series, manganese, reacts upon the oxidized salts of the 

 following metals and precipitates them as sulphides, the precipitating 

 agent at the same time going into solution as an oxidized salt. In a simi- 

 lar manner the sulphide of any other member reacts upon the oxidized 

 salts of all the following members, precipitating the sulphides of them 

 and going into solution as an oxidized salt. Thus the sulphide of iron 

 is a precipitating agent for the oxidized solutions of zinc, lead, copper, and 

 silver, throwing them down from their solutions as sulphides. Similarly 

 the sulphides of copper throw down silver as sulphide from oxidized silver 

 solutions. It is to be noted that the base metals, manganese, iron, and 

 arsenic, as sulphides, are capable of precipitating practically all of the 

 higher-priced metals; and that these compounds and zinc, lead, and copper 

 sulphides are capable of precipitating silver. It is thus shown by experi- 

 ment that the abundant sulphides of the baser metals are capable of pre- 

 cipitating, as sulphides, the more valuable metals from their oxidized salts. 

 In this connection the widespread occurrence of rhodocbrosite and 

 rhodonite in connection with ore deposits is very interesting. One or both 

 of these minerals are found in almost every Western camp. They have 

 been especially observed at the Butte and Little Belt Mountains districts 

 of Montana, and the San Juan, Cripple Creek, Rico, and Aspen districts of 

 Colorado. If manganese should be present in the veins as a sulphide, for 

 instance, as alabandite (MnS), and oxidized solutions of any of the other 

 metals come in, the sulphides of these other metals would be formed and 

 the manganese would pass to the oxidized condition, and it is found as a 

 carbonate or silicate in the deposits of the first concentration and frequently 

 as a hydrated oxide in the deposits which have been affected by secondary 

 alterations by descending waters. The oxidized manganese is precipitated 

 as a carbonate or silicate because carbonic and silicic acids are the two 

 abundant rock-making acids, and because these acids, with manganese, 

 make insoluble compounds. When later the rhodochrosite and rhodonite 

 in the belt of weathering are affected by secondary alterations, hydrated 

 oxide of manganese, so prevalent in the upper parts of deposits, is pro- 

 duced. It at 4 least is a suggestive coincidence that the rich gold streaks 

 in the Camp Bird mine, Colorado, are closely associated with impure 



"Purington, C. W., Woods, T. H., and Doveton, G. D., The Camp Bird mine, Ouray, Colo.: Trans. 

 Am. Inst. Min. Eng., vol. 33, 1903, p. 570. , 



