Researches on the Salts of Selenious Acid. 



29 



Represented in 100 parts: 



found 



calculated 



1. 2. 



Soda 20.52 20.52 



Selenious acid . . 73.31 73.32 

 Water (loss). ... 6.17 6.16 



V 2 Na 2 31 20.53 

 SeO 2 111 73.51 

 7,H 2 5.9G 



100.00 100.00 



151 100.00 



Berzelius employed tliis salt to prove the existence of diselenites. 

 For this purpose, it was carefully melted; but, in spite of all precautions, 

 he was not able to prevent a small quantity of selenious acid being carried 

 off with the water. On this account, the soda determination of the fused 

 salt, made in the same manner as that of the neutral salt, proved to be a 

 little too high, or 22.17 p. ct. instead of the calculated 21.83 p. ct. 



For reasons unknown to me, MuspratT seems to have arrived at a 

 contrary result; he says namely: "the biselenite does not suffer decomposi- 

 tion except at a very high temperature". Under this empression, and as 

 "it parts on a sand-bath only with its water of crystallization", he heated 

 the salt in this manner without determining" the temperature even approxi- 

 mately, then finds a loss of weight of 10.41 p. ct., assumes this to be ex- 

 pelled water of crystallization and finds this number casually agreeing with 

 a formula Na 2 O.Se0 2 -f- H 2 O.Se0 2 -f- 2H 2 0, which is assumed to express the 

 real composition of the salt, though no other ingredient has been determi- 

 ned. I need scarcely remark that Berzelius' observation, regarding the 

 phaenomena presented by the salt on heating, is true and that nearly half 

 the loss of weight, obtained by Muspratt, consisted in selenious acid that 

 had sublimated. 



A solution, obtained by treating 1 mol. carbonate of sodium with 4 

 mol. selenious acid, afforded this salt readily in very large, glass-shining, 

 hard, probably monoclinic prisms in combination with ortho- and klino- 

 diagonal end-faces, of which the predominant one gave a laminar form to the 

 crystals, and with terminal face, hemi-pyramid, dome etc. The salt has a 

 tendency to effloresce and is permanent both in ordinary and dry air. 



Analyses: 



1) 0.571 gr: salt gave 0.3193 gr. selenium or 0.4586 gr. selenious acid and 

 0.143 gr. sulphate of sodium or 0.0624 gr. soda. 



4. Tetraselenite: NaH.0 2 .SeO + H 2 .0 2 .SeO, 



