198 CLAUSTHALTTE. 



solution mixed with hydrochloric acid, heated for some 

 time to boiling, and the sulphuric acid precipitated by 

 chloride of barium. The excess of baryta in the fil- 

 tered solution is then precipitated by sulphuric acid, 

 and afterwards the selenium by sulphurous acid. 



In order to prepare selenious acid, the selenium is 

 dissolved in nitric acid, carefully evaporated to dryness, 

 and the acid sublimed in a retort. 



To prepare selenic acid, the selenious acid is satu- 

 rated with pure carbonate of copper and chlorine passed 

 into it until all the selenious salt is dissolved. The 

 solution is then again saturated with carbonate of cop- 

 per, concentrated by evaporation, and the selenate of 

 copper precipitated by alcohol, the chloride of copper 

 remaining in solution. The precipitate is first washed 

 with alcohol, then dissolved in water and the copper 

 precipitated by sulphuretted hydrogen. 



107. CLAUSTHALITE. (SELENIDE OF LEAD.) 

 PbSe. 



The analysis is best effected, like that of tetrahedrite 

 (No. 63), by means of chlorine-gas (Fig. 21). After the 

 decomposition, the bulb is again weighed, in order to 

 ascertain the amount of lead present. The greater part 

 of the selenium is volatilized in the form of the solid 

 chloride ; only a small quantity of the liquid chloride 

 passes over at first. These are conducted into water, 

 which is afterwards saturated with chlorine, in order 

 to convert all the selenious acid into selenic acid ; the 

 latter is then precipitated by chloride of barium, and 

 the selenium determined as selenate of baryta; 100 

 parts of the latter correspond to 28.2 of selenium. 



