Dr Turner's Analysis of' Euchroite. 303 



potash, which had been prepared by means of alcohol, was 

 added in such excess as to separate all the arsenic acid from 

 the oxide of copper. After due ebullition and washing, the 

 latter was collected on a filtre, ignited, and weighed. By 

 this process, 4.925 grains of the peroxide of copper were ob- 

 tained. 



The alkaline solution was rendered acidulous by nitric acid, 

 and then evaporated to dryness to obtain a perfectly neutral 

 solution, and to separate a minute quantity of silica which had 

 been dissolved by the potash. The arsenic acid was then 

 precipitated by a neutral solution of the nitrate of lead. This 

 operation was performed at a boiling temperature, and with 

 as slight an excess of the precipitant as possible, to prevent 

 the nitrate from combining with the insoluble arseniate of 

 lead ; — an inconvenience complained of by Berzelius in the 

 case of phosphoric acid, and which I have repeatedly felt my- 

 self, when precipitating arsenic acid by the acetate of lead. 

 A very pure arseniate of lead was thus procured ; but on eva- 

 porating the clear solution by a gentle heat to dryness, and 

 re-dissolving the soluble parts, an additional portion of the 

 arseniate was obtained, — showing that all the salt had not 

 fallen in the first instance. The arseniate of lead, after being 

 heated to redness, weighed 9-955 grains, equal to 3.399 grains 

 of arsenic acid, on the assumption that arseniate of lead con- 

 tains 34. 14 per cent, of acid. 



The anhydrous Euchroite consists, therefore, of 



Peroxide of Copper, 4.925 58.97 



Arsenic acid, 3.399 40.7 



8.324 99.67 



The crystallised mineral is composed of 



Peroxide of Copper, 47.85 

 Arsenic acid, 33.02 



Water, 1H.8 



99.67 



Did phosphoric acid exist in Euchroite, it would of course 

 be present in the arseniate of lead. On decomposing a por- 



