Researches on the Salts of Selenious Acid. 



43 



difference in the found quantities of oxide of lead is easily intelligible; the 

 mean of both determinations agrees closely with the theory. Like the 

 preceding bivalent metals, lead, consequently, does not give any tetraselenite. 



SELENITES OF MAGNESIUM. 



1. Neutral: Mg.0 2 .SeO + 6H 2 0. 



If selenite of sodium be added to a tolerably concentrated solution 

 of chloride of magnesium, so abundant a crystallization is obtained in a few 

 moments, that the whole solution is filled with a magma of microscopic, 

 six-sided, very thin, rhombic laraels with the acute angles truncated. On 

 employing a more dilute solution, the precipitate is formed by very small, 

 prismatic crystals. Both forms are of the same composition; the analyses 

 1 — 4 refer to the lamelliform, 5 — 6 to the prismatic salt. 



Analyses: 



1) 0.8283 gr. salt gave, after heating to whiteness in the blast-flame, 

 0.1283 gr. magnesia. 



2) 0.514 gr. salt gave 0.155 gr. selenium or 0.2178 gr. selenious acid. 



3) 0.5345 gr. salt gave 0.161 gr. selenium or 0.2262 gr. selenious acid. 



4) 0.5855 gr. salt, kept over sulphuric acid, did not change in the weight, 

 but lost 0.2115 gr. att 100°. 



5) 0.4423 gr. salt gave, after heating to whiteness, 0.0663 gr. magnesia. 



6) 0.4713 gr. salt gave likewise 0.0705 gr. magnesia. 



Centesimally represented : 



experiment theory 

 Magnesia . . . 15.49 — — — 14.99 14.97 MgO 40 15.44 

 Selenious acid — 42.37 42.32 — — SeO 2 111 42.86 



Water — — — 36.12 — — 6H 2 108 41.70 



259 100.00 



Of the 6 mol. water of crystallization which the salt contains, 5 are 

 expelled at 100°. Muspratt's statement: "selenite of magnesia, heated over 

 the lamp, gives off only its water of crystallization", is more than questio- 

 nable; on account of a water determination, undoubtedly performed in this 



