4 



L. F. Nilson, 



niac is not carried so far as to cause sublimation of the selenium, which 

 remains when the mass is extracted with water. 



Wohler J ) employed two different methods. The seleniferous deposit 

 was mixed with nitrate and carbonate of potassium and deflagrated: it was 

 then uninterruptedly boiled with hydrochloric acid, in order to convert the 

 selenic acid into selenious acid, which then was reduced with sulphurous 

 acid. The other method consisted in igniting the seleniferous deposit with 

 black flux, and extracting by means of boiling water the selenide of potas- 

 sium thus formed. This solution, when exposed to the air, oxidates and 

 yields the selenium. 



Another procedure is suggested by Bottger 2 ) and recommended by 

 Otto 3 ). It depends upon the circumstance that the selenium which exists 

 uncombined in the above-mentioned deposit, is dissolved by boiling with 

 sulphite of sodium, forming selenio-hyposulphite, from which selenium is 

 precipitated by hydrochloric acid. 



As regards the three methods first mentioned, they seemed to me 

 to require operations so troublesome, that I was inclined, without hesitation, 

 to give the preference to Bottger\s method. In order to try its applica- 

 bility, 2 kilogrs. of the deposit, completely washed and dried, were boiled 

 with a concentrated solution of 425 grs. crystallized sulphite of sodium, in 

 accordance with the given direction, until the mass was quite black. The 

 filtrate being treated with hydrochloric acid, not even a trace of selenium 

 was precipitated, but only a few flakes of sulphur with its peculiar yellow- 

 ish colour. The method was consequently unavailable. And the cause is 

 easily intelligible. It lies namely in the presence of the sulphate of lead, 

 which is transposed with the seleniohyposulphite, first really formed, so 

 that sulphate of sodium, selenide of lead and sulphurie acid are formed: 



Na 2 . O 2 . SSeO + Pb. O 2 . SO 2 + H 2 = Na 2 . O 2 . SO 2 + Pb. O 2 . SSe O + H 2 



PbSe~+ H 2 . O 2 . SOR 



That such a transposition really takes place, was confirmed, in the 

 first place, by the circumstance that, although the mass, by washing, had 

 been wholly purified from free sulphuric acid, yet sulphurous acid, during 

 the boiling, was continually disengaged, owing to the action of the free 

 sulphuric acid thus produced on an excess of sulphite of sodium; and, mo- 



') Berzelius Lehrb. d. Chemie 2 Bd. S. 198. Annal. d. Chemie u. Pharm. 

 XCI S. 122 (1843.) 



2 ) Journ. f. prakt. Chemie XCIV S. 439. 



3 ) Lehrb. d. Chemie 4:te Aufl. I S. 634. 



