OF MAGNESIA. 305 



8. Arseniate of magnesia may be prepared by 

 mixing together rather diluted solutions of sul- 

 phate of magnesia and arseniate of soda in the 

 atomic proportions. Little immediate change 

 is produced, but a portion of arseniate of mag- 

 nesia gradually precipitates in a fine white loose 

 state, very similar in appearance to native hy- 

 drate of magnesia. When the mixture is set aside 

 for twenty-four hours, a number of crystals of 

 arseniate of magnesia make their appearance in it. 

 They are small transparent four-sided flat prisms, 

 with very oblique terminations ; they constitute 

 tufts of crystals, radiating from a centre, and are 

 formed in the portion of the salt which has the 

 form of a powder. These crystals, when dry, 

 are transparent and tasteless. They are slightly 

 soluble in water though that liquid after be- 

 ing saturated with the salt in a boiling heat, has 

 no perceptible taste, and 1000 parts of boiling 

 water dissolve only 1 '5 parts of these crystals. 

 19*25 grains of these crystals, when exposed on 

 the sand bath to a heat of about 500, lose 6-75 

 grains of weight, and when exposed to a low red 

 heat the loss amounts to 9 grains. As these 

 crystals have no action on vegetable blues, they 

 are evidently neutral : hence, the constituents are 



1 atom arsenic acid 7*75 

 1 atom magnesia 2-5 



8 atoms water 90 



19-25 

 VOL. II. U 





