GOLD IN SURFACE ALTERATIONS OF ORE BODIES 325 



was noted in experiment 3 as carried out by the writer, it is possible 

 that in a longer time some loss might be detected, as more dilute solu- 

 tions act more slowly. 



SUMMARY 



From the above experiments it appears: 



1. That at the dilution of natural solutions of ferric salts their 

 solvent effect on gold is probably very slight; 



2. That in the presence of manganese dioxide no increased solu- 

 bility is found unless chlorides are present;' 



3. That mixtures of ferric sulphate, sulphuric acid, and sodium 

 chloride in concentrations common in mine waters will readily dis- 

 solve gold in the presence of manganese dioxide ; 



4. That free hydrochloric acid in the presence of manganese dioxide 

 has a much greater solvent effect than the same amount of chlorine 

 in ferric chloride solution; 



cipitant for gold. McCaughey, however (op. cit., footnote, p. 1270), failed to detect 

 any ferrous salt after the action had gone on for two days. It seemed probable that 

 ferrous chloride had been formed, but was oxidized by contact with the air. Accord- 

 ingly the experiment was repeated in an atmosphere of carbon dioxide, care being taken 

 to exclude, as far as possible, all contact with the air. Several possible sources of 

 error were not eliminated and the experiment is only of preliminary nature. The 

 results were as follows: 



This seems to establish the correctness of the equation given above. The result is 

 not in accord with the statement of Mcllhiney {Am. Jour. Set., Ser. IV, II, 293) who 

 found that gold dissolved in ferric chloride only in presence of air. The greater 

 dilution at which he worked may account for this. 



I The influence of manganese compounds in chemical reactions involving oxida- 

 tion is noted in many cases. E.g., Moissan (Chim. Minerale, V, 617) states that fuming 

 hydrochloric acid in presence of air will dissolve gold, especially if manganous chloride 

 is present. The catalytic action of manganese dioxide in the decomposition of potas- 

 sium chlorate and hydrogen peroxide are well known. Probably manganese com- 

 pounds are of considerable importance in natural oxidations, even though they may 

 be present in very small amounts. 



