70 MR. H. A. SMITH ON ARSENIC IN 



The pyrites used for the analyses given in Table II. was 

 the Hard Norwegian. 



Before going further I may mention that the methods 

 of analysis employed were as follows : — 



A weighed quantity of the ore was fused with three 

 parts of pure carbonates of soda and potash, and one part 

 pure nitrate of potash, for about ten minutes. The addi- 

 tion of chloride of sodium was, I found, perfectly unneces- 

 sary for the estimation of the arsenic. The residue was 

 then boiled well with water and filtered ; the insoluble por- 

 tion was again treated in the same manner, and the filtrate 

 from it added to that of the former. This filtrate* was care- 

 fully evaporated to one quarter of its bulk, and the arsenic 

 determined by two separate methods, — 1st, by precipitation 

 as tersulphide of arsenic ; and, 2ndly, as the arseniate of 

 ammonia and magnesia, both dried on a weighed filter. 



The methods of analysis of the products obtained from 

 the sulphuric acid were simply modifications of this process, 

 the unnecessary portions being omitted. 



The numbers given in Part i of Table I. show, I think, 

 a little anomaly at the outset. As in practice we find that 

 the great difficulty a manufacturer has to contend against 

 in burning pyrites is the arsenic, he will naturally prefer 

 the ore with the least objectionable matter present. Here 

 we find four species with only a " trace " of arsenic present, 

 and one with actually " none." I do not think manufac- 

 turers, as a rule, would run so much against their own 

 interests as to use a pyrites containing arsenic when they 

 could buy another kind free from it; but, according to 

 this analysis, they must make a great error, as I believe 

 there is a pretty fair demand for both Belgian and West- 

 phalian pyrites, and that even Spanish finds ready cus- 

 tomers, although the Nonvegian is said to be free from 

 arsenic impurity. I am afraid we must lay this fact not 

 altogether to the stupidity of the manufacturers, but partly 



