82 FACTS IN AMERICAN MININO. 



appearance, and gold is being lost without amalgamation. The 

 tendency in this country appears to be to use too much mercury. * 



Loss or Gold. 



In the year 18G7 it was computed that the general loss in the 

 treatment of gold quartz averaged from 20 to 42 per cent, through 

 the State, but the subsequent introduction of improved pans for 

 the treatment of tailings is supposed to have reduced the actual 

 loss in some cases as low as 5 per cent, on the fire assay, 

 when no sulphurets are present. 



Chlorination. — The Californians concentrate and roast their 

 pyrites by the usual methods, and appear to look with great favour 

 upon the process of chlorination as a method of extracting the 

 fine gold therefrom. The Commissioners speak of its success with 

 confidence, and in my opinion without sufficient reservation. 

 There certainly are conditions under which the process can be used 

 with great advantage, but I believe they are exceptional. Those 

 under which it appears to be not applicable — and which appear 

 not to have been noticed by the Commissioners — are well known 

 to metallurgists, and are as follow : — 



When the pyrites are imperfectly roasted. 



When any silver is present, as it becomes chloridized, coats the 

 gold, and prevents it being attacked. 



When any antimony or arsenic are present, and antimony gets 

 converted into chloride and precipitates the gold. 



When, through careless or imperfect roasting, sulphates are 

 formed ; as when metallic iron is present, as in either of these 

 cases the gold would be precipitated. 



When lime or carbonate of lime is present, as they absorb the 

 chlorine. 



When the gas is imperfectly purified, and hydrochloric acid 

 carried over, as it will react on some metals, producing sulphuretted 

 hydrogen, which will precipitate the gold. 



As a general rule the gold in pyrites is fine, but I have known 

 large nuggets of gold enveloped in pyrites, and these would be 

 liable to be lost unless the operation were protracted beyond the 

 usual time allotted to the process. Some years since, Mr. H. A. 

 Thompson condemned chlorination as a commercially practicable 

 process, in the columns of the Sydney Mail ; I then defended it, 

 but subsequent closer study of the question has developed 

 difficulties, affording me the gratification of recognising Mr. 

 Thompson's superior acquaintance with the subject. Whatever 

 may be the character of the pyrites in California or the skill of 

 the millmen, I think that in New South Wales a very small per- 



* It is a common practice in New South Wales to add every hour two spoonfuls or a, 

 tablespoonful of mercury, quite regardless of the coudition of the amalgam. 



