MANGANESE IN GOLD DEPOSITS 31 



silver mines, tabulated above. It is believed to be of very sub- 

 ordinate importance in connection with the solution of gold. 



The efficiency of ferric iron and cupric copper to supply nascent 

 chlorine, compared with that of manganitic manganese. — Solutions 

 of ferric sulphate with sulphuric acid and salt dissolve gold at high 

 temperatures. Concentrated solutions of ferric sulphate and 

 hydrochloric acid dissolve gold at from 38 to 43 C. In the cold 

 the reaction may go on in concentrated solutions, but in those 

 approximating the concentration of mine waters no weighable 

 loss of gold was obtained. With Mn0 2 under the same conditions 

 there was a very appreciable loss in a solution containing only 

 1.4 gm. of CI in a liter. It appears, therefore, that the action of 

 ferric iron on gold in cold dilute mine waters with H 2 S0 4 and 

 NaCl is probably negligible; for the experiments with ferric iron 

 in such solutions, without manganese, extended over a period of 

 34 days without weighable loss of gold. 



Many auriferous deposits contain copper, but since the reactions 

 which give nascent chlorine are conditioned upon the presence of 

 some element that changes its valence in the reactions, and since 

 the processes underground take place in sulphate solutions, it did 

 not appear necessary, after ferric salt had been shown to be incom- 

 petent, to conduct experiments with copper; for, as is well known, 

 cuprous salts have never been detected in acid sulphate mine 

 waters, whereas ferric and ferrous sulphate are very common in 

 such waters. It has been shown 1 however that the efficiency of 

 cupric salt in cold solution compared with that of manganitic salt 

 probably lies somewhere between 0.004 an d 0.000001. 



Amount of chlorine necessary for the solution of gold with man- 

 ganese compounds present. — In experiment 15 (a), with Mn0 2 , 

 0.01640 gm. of gold was dissolved in 34 days with solution one- 

 tenth normal with respect to chlorine. A solution with but 40 

 per cent as much CI (experiment 16b) dissolved 31 per cent as much 

 gold in 14 days as was dissolved in the more concentrated solution 

 in 34 days. These results show that in 15 (a) conditions are prob- 

 ably approaching equilibrium, and also that the solvent power of 

 chlorine is approximately proportional to the amount present. 



1 Bull. Amer. Inst. Mining Eng., 790 (October, 1910). 



