SELENIFEROUS DEPOSIT. 195 



stream of hydrogen, and the reduced pyrophoric 

 mass allowed to fall, immediately, into dilute hydro- 

 chloric acid, which dissolves the iron, leaving the 

 uranium a protoxide. 



In order to detect selenium, arsenic, and vanadium 

 in pitch-blende, it is ignited with J of its weight of a 

 mixture of carbonate of soda and nitre. The sele- 

 nates, vanadates and arsenates of the alkalies may then 

 be extracted with water. 



105. SELENIFEROUS DEPOSIT FROM SULPHURIC 

 ACID CHAMBERS. 



(Sulphate of lead, selenium, selenide of mercury, 

 selenates selenites, &c.) 



The dry mass is rubbed to a thin paste with a mix- 

 ture of about equal parts of sulphuric acid and water, 

 and boiled for a long time, concentrated nitric acid or 

 chlorate of potassa being added at intervals, to oxidize 

 the free selenium, until all the reddish color has dis- 

 appeared. 



The mixture is then diluted with water and filtered. 

 The solution contains, besides iron, copper, mercury 

 and a little lead, all the selenium as selenious and 

 selenic acids. It is mixed either with about as much 

 common salt as amounts to half the weight of the 

 deposit originally employed, or with J of its volume 

 crude of fuming hydrochloric acid, and boiled down 

 to about J of its original bulk. The hydrochloric 

 acid reduces the selenic acid to selenious acid. 



On cooling, the solution is poured off from any 

 sulphate of potassa and common salt which may have 

 been deposited ; these are washed several times with 

 water, and the solution saturated with sulphurous acid 

 gas, evolved from a mixture of powdered charcoal and 

 concentrated sulphuric acid. 



