Researches on the Salts of Selenious Acid. 



5 



reover, by the fact that selenio-hyposulphite was really first formed, because 

 the solution that was obtained by boiling the mass with sulphite of sodium 

 only for a few moments, on adding hydrochloric acid, afforded a large 

 precipitate of pink selenium, whereas its quantity, on further boiling, gradually 

 diminished and finally quite disappeared. Thus for instance, a small quantity 

 of the deposit, treated for a minute in this manner, gave a solution which 

 with hydrochloric acid separated only sulphur. 



This method is consequently quite unfit for producing selenium from 

 the seleniferous residue of the leaden chambers, whenever the latter contains 

 any compound which, like sulphate of lead, exercises a disturbing influence 

 on the operation, because it is impossible to prevent the almost instantaneous 

 decomposition of the selenio-hyposulphite of sodium into insoluble selenide 

 and soluble sulphate. 



Already in the year 1840 Wiggers l ) proved that selenium, like 

 sulphur, may be dissolved in boiling cyanide of potassium, which was later 

 confirmed by Wohler 2 ); and Rose 3 ) has found that, from a mixture of 

 sulphur and selenium, it chiefly extracts the latter. This property of a so- 

 lution of cyanide of potassium and the relation of the thus formed seleno- 

 cyanide of potassium to hydro-chloric acid, when the liberated selenocyanic 

 acid resolves itself into hydro-cyanic acid and free selenium, has, accor- 

 ding to Otto 4 ) been made use of to extract selenium from "Flugstaub". To 

 this statement, however, he adjoins the remark that cyanide of potassium 

 is by uo means preferable to the cheaper sulphite of sodium. 



In the case of the seleniferous residue from Falun, this method pro- 

 ved very simple and profitable. It most decidedly has the advantage of 

 Bottger's method and every other hitherto known. Even for obtaining 

 selenium from "Flugstaub", the mode of proceeding proposed by Bottger 

 seems to me inapplicable, or at least less profitable, for as this latter sub- 

 stance contains, among other things, also sulphate of copper it would pro- 

 bably be impossible to prevent a decomposition of the selenio-hyposulphit of 

 natrium formed, by which at least some part of the selenium that is con- 

 tained in the Flugstaub, remains in the residue as insoluble selenide of copper. 



In order to obtain selenium from the seleniferous deposit, I have 

 found it best to proceed in the following manner. 



A quantity of ordinary cyanide of potassium is dissolved in warm 

 water to tolerably strong concentration, and then allowed to act upon the 



') Ann. d. Chemie u. Pharm. XXIX S. 319. 



2 ) Ann. d. Chemie u. Pharm- CIX S. 125. 



3 ) Ann. d. Ph. und Ch. CXIII S. (324. 



4 ) Lehrb. d. Chemi 4:te Aufl. I. S. 634. 



