08 



MR. H. A. SMITH ON ARSENIC IN 



tion and allowed to cool, the undissolved oxide sinks to 

 the bottom of the tube ; but on still further cooling, when 

 the contents of the tube are about to solidify, the oxide 

 rises from the bottom and mixes with the oxychloride. To 

 obtain the substance perfectly free from the undissolved 

 oxide, the contents of the tube are gently heated, and, 

 when the finely divided oxide is deposited, the clear liquid 

 oxychloride is drawn oft' with a pipette. 



IX. Arsenic in Pyrites and various Products. By H. A, 

 Smith. Communicated by Professor Roscoe, F.R.S. 



Kead April 4th, 187 1. 



The presence of arsenic in the various kinds of pyrites used 

 for the production of sulphuric acid has been a great draw- 

 back to manufacturers from its first introduction, and has 

 prevented the use of this mineral to the extent it might 

 otherwise have attained. 



The arsenic, difficult to get rid of commercially, passes 

 from the pyrites to the sulphuric acid, from the acid to the 

 products in the manufacture of which the acid has been 

 employed, its presence alone preventing their use in very 

 many case*. 



In the analyses I have seen given of pyrites the amount 

 of arsenic present seems very trivial ; and, indeed, had the 

 specimens analyzed been fair samples of the general ores 

 supplied to manufacturers, there would be little or no 

 necessity for complaint. The difference existing between 

 the, amount of arsenic in pyrites obtained by laboratory 

 analysis and that found in practical working led me to 



