MANGANESE IN GOLD DEPOSITS 29 



In the 29 analyses of mine waters N0 3 is reported from but 

 one. Possibly nitrates are more abundant than is indicated by 

 the analyses; and if so, they must increase the solvent power of 

 chloride solutions; but the data at present available do not indi- 

 cate that they affect the superficial reactions to any important 

 extent. 



Manganese oxides. — That gold is dissolved in moderately dilute 

 solutions containing salt and manganese oxides is shown by experi- 

 ments n, 15, and 16. The reaction with manganese used to 

 prepare chlorine commercially is illustrated by the following 

 equation. (The reaction is not so simple as stated. It is discussed 

 later.) 



Mn iiii 2 +2NaCl+3H 2 S0 4 ->2H 2 0+ 2 NaHS0 4 +Mn ii S0 4 +2Cl. 



At the beginning of the reaction the manganese has a valence of 

 four; at the end a valence of two. With acid the reaction may be 

 as follows: 



Mn0 2 + 4 HCl-> 2H 2 0+MnCl 2 +Cl 2 . 



Besides the presence of a chloride, some other conditions are 

 essential to the solution of gold. There appear to be two. One 

 is that some other substance must also be present which is capable 

 of being reduced so as to liberate chlorine — as, for example, a ferric 

 salt which may be reduced to the ferrous, a cupric to the cuprous, 

 the higher manganese salts to the lower, etc. The other is the 

 evolution of ''nascent" chlorine. This is particularly illustrated 

 by the action of aqua regia or the production of chlorine by hydro- 

 chloric acid and pyrolusite. In short, any of a number of methods 

 of producing free chlorine would be effective in the solution of 

 gold. Possibly both of the conditions just mentioned may in the 

 last analysis be identical. The essential point is that the atomic 

 chlorine in a state of molecular exchange or evolution is able to 

 combine with the gold. For present purposes the gold may be 

 considered to dissolve as gold chloride, although chemical investi- 

 gations favor the theory that a complex ion containing gold is 

 formed. The only consideration which becomes important in its 

 geological aspect is the presence of the compounds which not only 



