508 MAGNKSIUM. 



that one equivalent of water is essential to the existence of this 

 and all other nitrates of the magnesian class of oxides. That 

 water is not displaced by nitrate of potash heated in contact 

 with the magnesian nitrate. Nitrate of magnesia is very so- 

 luble in alcohol, and forms a solid alcoate, in which probably 

 a portion of water is associated with the alcohol. I did not 

 succeed in forming a double nitrate of magnesia and ammonia, 

 (nor any other double nitrate), although such a salt is admitted 

 by Berzelius. 



Phosphate of magnesia is formed on mixing cold solutions of 

 common phosphate of soda and of sulphate of magnesia, and 

 allowing the liquid to stand for 24 hours. The salt appears in 

 tufts of slender prisms, which effloresce in dry air. They 

 are soluble in about 1000 times their weight of water. The 

 composition of this salt, which I carefully examined, may be 

 expressed by the following formula, HO, 2Mg O, PO 5 + 2HO -f 

 12HO. (Phil. Trans. 1837.) 



Phosphate of magnesia and ammonia. This is the well-known 

 granular precipitate, which appears, when a tribasic phosphate 

 and a salt of ammonia are dissolved together, and any salt of 

 magnesia is added to the mixture. Its formation is had re- 

 .course to as a test of the presence of magnesia. Although in- 

 soluble in a liquid containing salts, it is so soluble in pure water 

 that it cannot be washed without sensible loss. It is readily 

 dissolved by acids. The same substance forms the basis of 

 the variety of urinary calculus, known as the ammoniaco-mag- 

 nesian phosphate. It is a tribasic phosphate, of which the 3 

 atoms of base are 1 atom of oxide of ammonium and 2 atoms 

 of magnesia, with 1 2 atoms of water of crystallization ; ten of 

 the latter may be expelled without any loss of ammonia. The 

 formula of this salt is therefore NH 4 O, 2Mg O, PO 5 + 2HO + 

 10HO. Dr. Otto has observed a corresponding tribasic phos- 

 phate of protoxide of iron and ammonia, which contains only 

 two atoms of water of crystallization ; and also an arseniate of 

 manganese and ammonia, of which the water of crystallization 

 appears to be the same as that of the phosphate of magnesia and 

 ammonia. 



Borate of magnesia. The neutral salt was obtained by 

 Wohler, in the form of crystals, by heating a mixture of the so- 

 lutions of sulphate of magnesia and borax to the boiling point, 

 to form a precipitate, and allowing the liquid to digest for 



