164< Dr. Percy on the Composition of Beudantite. 



but, after long standing, no trace of crystalline precipitate 

 appeared. 



First Analysis. 



In this analysis the crystals employed were not selected 

 under a lens, and were mixed with some amorphous brown 

 matrix. 



Weight of mineral after drying at 130° C._, 6*17 grains. 

 The colour of the powder was light brown. 



It was fused with more than 20 grains of a mixture of car- 

 bonate of potash and soda. The product was thoroughly 

 washed with hot water and the solution filtered. 



Solution (a) and Residue (b) 



Solutiofi (a). Colourless. Excess of hydrochloric acid was 

 added. It way then boiled with a little sulphite of potash, 

 after which sulphuretted hydrogen was passed through it. A 

 reddish-brown precipitate was produced, which after standing 

 all night in a warm place, was covered with a fine yellow pre- 

 cipitate." Some lead had evidently been dissolved by the ex- 

 cess of alkaline carbonate*. The precipitate was washed with 

 water and afterwards digested with hydrosulphate of ammonia. 



A minute quantity of black matter remained undissolved 

 upon the filter, upon which the sulphuret of lead subsequently 

 separated from the insoluble residue (b) was collected. 



The filtrate was treated with excess of hydrochloric acid, and 

 left in a warm place more than twenty-four hours. The pre- 

 cipitate, which evidently consisted chiefly of free sulphur, was 

 analysed in the usual way for arsenic. Weight of precipitate 

 after drying until it ceased to lose weight, 2*08 grains. It 

 was boiled with the strongest nitric acid. Globule of free 

 sulphur, washed and dried, weighed 0*65. To the acid so- 

 lution excess of chloride of barium was added. The sulphate 

 of baryta obtained, washed, dried and ignited, weighed 7'55. 



The solution, from which the arsenic had been precipitated 

 as sulphuret, was reduced to a small volume by evaporation. 

 Sulphate of magnesia, hydrochlorate of ammonia, and am- 

 monia were then added. The crystalline precipitate was 

 washed on the following morning with cold ammonia-water. 

 Dried and ignited it weighed 0*14 gr. 



Hesidue (b). It was dissolved in hydrochloric acid. Sul- 

 phuretted hydrogen was passed through the solution. The 

 precipitate was collected on the filter before-mentioned. It was 

 digested with the strongest nitric acid, a little sulphuric acid 



* I have found that when a solution of carbonate of potash is long kept 

 in & flint-glass bottle, it dissolves a very sensible amount of lead. 



