SELENIUM. 177 



nitric acid, gave poor results ; better figures were obtained 

 upon reducing SeOa with ammonium bisulphite and hydro- 

 chloric acid, and determining the percentage of selenium 

 set free : 



.6800 grm. SeOj gave .4828 grm. Se. 71.000 per cent. 



3.5227 " 2.5047 " 71.102 " 



4.4870 " 3-1930 " 71. 161 



Mean, 71.0S8, i .032 



In a similar manner Sacc also reduced barium selenite, 

 and weighed the resulting mixture of barium sulphate and 

 free selenium. Tliis process gave discordant results, and a 

 better method was found in calcining BaSeOg with sul- 

 phuric acid, and estimating the resulting quantity of BaSO^. 

 In the third column I give the amounts of BaSO^ equivalent 

 to 100 of BaSeOg : 



•5573 S^'^- BaSeOg gave .4929 grm'. BaSO^. 88.444 



.9942 " .8797 " 88.383 



.2351 " .2080 " 88.473 



.9747 " .8621 " 88.448 



Mean, S8.437, ± .013 



Still other experiments were made with the selenites of 

 silver and lead ; but the figures were subject to such errors 

 that they need no further discussion here. 



A few years after Sacc's work was published, Erdmann and 

 Marchand made with their usual care a series of experi- 

 ments upon the atomic weight under consideration.* They 

 alalyzed pure mercuric selenide, which had been repeatedly 

 sublimed and was well crystallized. Their method of ma- 

 nipulation has already been described in the chapter upon 

 mercury. These percentages of Hg in HgSe were found : 



71.726 



71-731 

 71.741 



Mean, 71.7327, ± .003 



* Journ. fur Prakt. Chem., 55, 202. 1852. 



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