ARSENIC AND ANTIMONY. 89 



phides, they may be at least approximately separated 

 by digestion with concentrated hydrochloric acid, 

 which dissolves the sulphide of antimony, and leaves 

 that of arsenic, or with carbonate of ammonia, which 

 dissolves the sulphide of arsenic. 



Methods for Quantitative determination. 



I. The compound is carefully oxidized with aqua- 

 regia, or with hydrochloric acid and chlorate of potassa, 

 some tartaric acid and a considerable quantity of chlo- 

 ride of ammonium -added, and the mixture then treated 

 with ammonia in excess, which must dissolve the 

 whole. From this solution the arsenic acid is precipi- 

 tated by sulphate of magnesia. (See No, 51,) 



The filtrate is acidulated with hydrochloric acid, 

 and the antimony precipitated by sulphuretted hydro- 

 gen, and treated as in No. 5. 



II. A more accurate method depends upon the fact 

 that freshly precipitated sulphide of arsenic is soluble 

 in sulphite of potassa and sulphurous acid, while the 

 sulphide of antimony is not. 



The analysis of commercial gray sulphide of anti- 

 mony or metallic antimony, is made in the following 

 manner : 



The very finely pulverized and weighed substance 

 is digested with a solution of sulphide of potassium 

 and some sulphur, until it is dissolved. There gene- 

 rally remains a black mixture of sulphides of lead, 

 iron, and copper, which are separated by filtration and 

 analyzed by themselves. The solution is then mixed 

 with a large excess of a saturated solution of sulphurous 

 acid in water, with this digested and kept at the boil- 

 ing-point until two-thirds of the water has evaporated, 

 and all the sulphurous acid is driven off. The precipi- 

 tated sulphide of antimony is filtered, washed, and 

 treated as in No. 5-1. From the solution which contains 



