286 M. Rose's Analysis of the [Oct. 



It is necessary not to overheat the bulb, lest a portion of chlo- 

 ride of lead should be volatilized. 



The selenium was thrown down from the liquid in the bottle 

 by sulphite of ammonia, muriatic acid having been previously 

 added to the liquid. The selenium was collected on a filter, 

 dried, and weighed. Although it is very easy to throw down 

 the whole of the selenium from a solution of selenic acid by 

 sulphurous acid, it is nevertheless very difficult to precipitate it 

 from a solution of chloride of selenium in water, through which 

 a current of chlorine has been passed for a long time. The 

 liquid must be digested a great while with sulphite of ammonia, 

 and frequently boiled, in order to obtain the whole of the sele- 

 nium. The iron was precipitated from the liquid, after the sepa- 

 ration of the selenium. The seleniurets which I analysed are 

 the following : — 



1. Seleniuret of Lead. — This was the most frequent seleniuret 

 in the minerals 1 received. It has internally so great a resem- 

 blance to sulphuret of lead as not to be easily distinguished 

 from that substance. Its colour is lead grey, its lustre very 

 metallic ; it occurs in masses imbedded in magnesian carbonate 

 of lime, from which, however, it may be very easily freed for 

 analysis by digestion in weak muriatic acid. Its fracture is 

 saccharoidal ; the granulations are of various fineness, the 

 coarsest distinctly exhibiting a lamellar cleavage, the directions 

 of which, however, I could not determine : it is brittle and soft. 



This mineral, purified by diluted muriatic acid, gives no sub- 

 limate, nor fuses, when heated by the blowpipe in a small tube 

 closed at one end. Heated in an open tube, a small quantity 

 of selenium sublimes, and hygrometrical crystals of selenic acid 

 are formed at the same time. The whole assay becomes sur- 

 rounded by fused yellow oxide of lead, and the tube is filled 

 with the peculiar odour of selenium. On charcoal it fumes, and 

 tinges the flame of the lamp blue by the combustion of selenium. 

 For some distance round the assay, the charcoal is covered with 

 sublimed oxide of lead, but no metallic lead is produced without 

 the addition of soda. The fluxes discover nothing but lead, 

 though some specimens give indications of iron, and one pre- 

 sented traces of copper. 



After all the experiments I had made with the blowpipe, a 

 quantitative analysis was almost useless ; only seleniuret of lead 

 could produce these phenomena. However, I analysed a very 

 pure specimen, in which not the slightest trace of either iron or 

 copper could be discovered by the blowpipe. 3*221 grammes 

 (60 grains) of the purified mineral treated with chlorine, gave 

 3-104 grammes (48 grains) of chloride of lead, equivalent to 

 2-313 grammes (35*8 grains) of lead, or 71-81 per cent. The 

 chloride of lead dissolved entmly in water without leaving any 



