64 PYROMORPHITE. 



powdered, and dissolved in caustic potassa. The lead 

 is precipitated from the solution by sulphide of ammo- 

 nium, filtered, dried, and as much removed from the 

 filter as possible. The filter is then burned and the 

 ashes added to the precipitate, which is then mixed 

 with a little sulphur, strongly heated in dry hydrogen 

 gas, and then weighed as sulphide of lead. 



The filtered solution is acidified with hydrochloric 

 acid, which precipitates any sulphide of arsenic, to be 

 treated as directed in the article upon copper-nickel. 

 (No. 65.) 



The liquid filtered from the sulphide of arsenic is 

 concentrated by evaporation, supersaturated with am- 

 monia, and the phosphoric acid precipitated by sulphate 

 of magnesia. (See No. 9.) 



The chlorine is determined in another portion, by 

 dissolving in nitric acid, and precipitating by nitrate 

 of silver. 



For the determination of lime, the mineral is dis- 

 solved in nitric acid, and the lead precipitated from 

 the diluted solution by sulphuretted hydrogen. The 

 solution filtered from the,sulphide of lead is neutralized 

 with ammonia, and the lime precipitated by oxalateof 

 ammonia. The filtrate is concentrated by evaporation, 

 mixed with ammonia, and the phosphoric acid preci- 

 pitated by sulphate of magnesia. 



Those specimens which are free from lime, but which 

 contain arsenic acid, maybe analyzed in the following 

 manner. The mineral, in a state of very fine powder, 

 is digested with moderately dilute sulphuric acid, the 

 greater part of the water evaporated, the mass mixed 

 with alcohol, and the sulphate of lead thrown upon a 

 filter and washed with spirit of wine. The filtrate is 

 evaporated to expel -the alcohol, arid a stream of sul- 

 phuretted hydrogen passed through it, while it is 

 heated to about 50. It is afterwards allowed to cool 

 while the gas is still passing, and, when saturated with 



