1835.] Improvements in Science. 113 



in a glass retort; a small quantity of acid liquor first 

 passes over, then sulphur follows, which condenses in 

 the receiver ; 100 parts of the dried matter contains 42 

 of sulphur. It should then be pulverised and boiled 

 with a concentrated solution of potash till the solution is 

 saturated with sulphur. Dilute the liquid with from four 

 to six times its volume of water, and expose it to the air. In 

 eight or ten days an efflorescence takes place on the surface 

 of the liquid, which, as it separates into considerable pieces, 

 sinks by shaking to the bottom of the vessel. When this 

 precipitation ceases the substance is to be well washed. It 

 consists of pure selenium. From the solution a light black 

 matter separates, which is 'carbon, and may be separated 

 from the selenium by filtration. If the solution is allowed 

 to remain for some days in the air, after the separation from 

 the selenium, a red powder collects on the surface, which 

 is a combination of sulphur, with a little selenium. 



To free the selenium first obtained from a small quantity 

 of sulphur, it may be again treated with potash, but in this 

 case, a small quantity of selenious acid remains in solution ; 

 or it may be oxidized by nitric acid, and precipitated with 

 sulphate of ammonia. 



In the same way the selenium may be separated from the 

 compound of sulphur and selenium, which appears to be a 

 combination of sulphuret of selenium with sulphur. If the 

 solution be exposed to the air after the separation of the 

 selenium and red compound, for six or eight weeks, more 

 sulphur is deposited, with a little selenium, which may be 

 separated by potash. 



A small portion of selenium still remains in the liquid, 

 which may be extracted by saturating the potash with mu- 

 riatic acid, and then treating the sulphur which separates 

 with potash as before. But it will be found that the quan- 

 tity obtained in this way is not worth the trouble of the 

 process. 



The black pulverulent residue which remains after the 

 distillation of the sulphur, contains a small quantity of 

 selenium. It consists of silicious sand, charcoal, lead, 

 lime, iron, alumina and sulphur. To separate the selenium 

 1 part of the matter is to be heated with 1 part of saltpetre 

 and 2 or 3 of common salt, in a crucible, until the black 



VOL. I. I 



