12 



L. F. Nilson, 



SELENITES OF POTASSIUM 



1. Neutral: K 2 .0 2 .SeO + H 2 0. 



This salt was prepared from carbonate and selenious acid, weighed 

 off in corresponding molecular quantities, and the solution continually boiled, 

 in order to remove all dicarbonate possibly formed. It was then allowed 

 to evaporate over sulphuric acid at the ordinary temperature, the syrupy 

 mass becoming filled with laminar, four-sided, probably rhombic prisms, 

 with the ends obliquely truncated on both sides. The salt is so deliquescent 

 that the crystals could not be collected and freed, by pressing, from mother- 

 liquor. In order to obtain the salt in a fit state for analysis, it was there- 

 fore dried over sulphuric acid to constant weight. 



Analyses : 



1) 0.5992 gr. salt gave 0.2115 gr. selenium or 0.2972 gr. selenious acid and 

 0.4715 gr. sulphate of potassium, containing 0.255 gr. potash. 



2) 0.9133 gr. salt gave 0.3239 gr. selenium or 0.4551 gr. selenious acid and 

 0.7108 gi*. sulphate of potassium, containing 0.3844 gr. potash. 



Centesimally represented : 



experiment theory 



1. 2. 



Potash 42.56 42.09 K 2 94.2 42.20 



Selenious acid. . . 49.60 49.83 SeO 2 111.0 49.73 



Water (loss) .... _JU4 8.Q8 H 2 8.Q7 



100.00 100.00 223.2 100.00 



Berzelius found this salt insoluble in alcohol; when alcohol is added 

 to the aqueous solution, the selenite that has but little tendency to cry- 

 stallize, separates as an oily layer under the alcoholic solution. Like the 

 other neutral selenites of the alkaline metals, it is persistent in a fused 

 state, if protected from the action of reducing gases; otherwise, it is par- 

 tially reduced to selenide of potassium. Muspratt communicates an analysis 

 of selenite of potassium showing an amount of 45.02 pr. ct. potash, without 

 mentioning, how the analyzed compound has been previously treated. This 

 amount of potash nearly agrees with the formula for waterfree salt, which 

 requires 45.91 pr. ct.; it is also possible that he had before him such a 

 salt, obtained by previous heating. 



