SELENIUM SOOT. 197 



It is necessary in this process that all the nitric acid 

 from the nitre should either be expelled or decomposed, 

 for otherwise part of the selenium will escape preci- 

 pitation. 



Or the solution of the fused saline mass is saturated 

 with hydrochloric acid, chloride of ammonium added, 

 evaporated to dryness, and the mass heated in a retort 

 until the chloride of ammonium begins to sublime, 

 when all the selenium is reduced. 



106. SELENIUM SOOT.* 

 (Selenium with Selenides, Coal, Sand, &c.) 



The black mass is moistened with sulphuric acid, 

 thoroughly washed, fully dried and distilled from a 

 porcelain or hard glass retort, with a strong heat, until 

 most of the selenium passed over nearly pure. 



The residue consisting of selenides, coal and other im- 

 purities, is dissolved in hydrochloric acid with gradual 

 addition of nitric acid, and while hot the copper 

 and iron are precipitated by caustic soda, the solution 

 filtered, and the selenium precipitated by saturating 

 with sulphurous acid, or reduced by adding an excess 

 of chloride of ammonium, evaporating to dryness and 

 heating until the chloride of ammonium begins to sub- 

 lime, when the alkaline salt is washed out. If the 

 selenium is precipitated directly from the solution 

 containing copper more or less of this metal is thrown 

 down. 



In order to detect and separate the sulphur in the 

 selenium, it is dissolved in very strong nitric acid, the 



* It collects in the chimneys where the copper ores are roasted 

 at Mansfeld. It contains from 30 to 40 per cent, of selenium 

 after it is washed and dried. 



17* 



