106 M. Lewenau on Selenium. [Aug. 



solution from which the selenium was precipitated, it was evapo- 

 rated to two-thirds of its bulk in a retort ; by these means small 

 grey spangles were obtained, possessing a metallic brilliancy, 

 and friable between the fingers : they were metallic selenium. 

 The concentrated liquor, mixed with sulphite of ammonia, 

 afforded a fresh quantity, but this had a dirty-brown colour. 

 The acid products of this distillation, collected in the receiver, 

 not giving any precipitate, nor becoming turbid with sulphite of 

 ammonia, bars of zinc were immersed in it ; the liquor being 

 previously divided into several portions, and diluted, to avoid a 

 too violent action : selenium was thus deposited, in dark-grey 

 flakes, with a brisk disengagement of hydrogen gas, of a pecu- 

 liar odour. It is necessary to separate these flakes speedily 

 from the liquor, or they soon disappear. The selenium thus 

 obtained was washed and dried. It must be observed in this 

 operation, that immediately after the precipitation of the sele- 

 nium, the bars of zinc should be removed from the acid, other- 

 wise there is danger that it may mix with the metallic particles ; 

 in that case, it is advantageous to wash them with water acidu- 

 lated with sulphuric acid. Finally, it may happen that all the 

 selenium may not be obtained by this method, for zinc does not 

 appear to be capable of precipitating it wholly from the solution. 

 " By the preceding process, one pound of the sulphureous 

 deposit afforded, 



Gros. grs. Grs. troy. 



" Red selenium, precipitated by sulphite of "1 ^ ,. __ aqa.\c 



ammonia J 



Dark-grey, obtained by zinc 48 = 39-67 



Metallic 12 = 9-92 



Impure, brown 1 0= 59*07 



*10 2 = 592-82 



" If we compare M. Lewenau's process with those successively 

 adopted by M. Berzelius, we find it very superior to any of them. 

 In fact, by the old methods, we perform many useless operations 

 for the purpose of freeing the solution of selenium from all 

 foreign substances, in order to precipitate it in a pure state. 

 This mode had serious inconveniences, in consequence of the 

 difficulty of separating the sulphuric acid, and the metallic 

 oxides, without at the same time their carrying with them a por- 

 tion of the selenium. M. de Lewenau avoids this, and at the 

 same time obtains a larger product by simplifying the operation." 



• The sulphureous deposit on which M. Lewenau made his experiments, was procured 

 from a sulphuric acid manufactory in Hungary. M. Henri, jun. has repeated the pro- 

 cess on the seleniferous sulphur from Falilun, and obtained a much smaller proportion of 

 selenium than was obtained by the author. — Note by M. Rdbinet. 



