2.96 NITROGEN. 



Nitric acid forms an important class of salts, the nitrates, 

 which occasion deflagration when fused with a combustible at 

 a high temperature, from the oxygen in their acid, and are re- 

 markable as a class for their general solubility, no nitrate being 

 insoluble in water. The nitrate of the black oxide of mercury is 

 perhaps the best soluble of these salts. In neutral nitrates the 

 oxygen in the acid is always five times that in the base. The 

 nitrates of potash, soda, ammonia, barytes and strontian, are 

 anhydrous ; but the nitrates of the extensive magnesian class of 

 oxides all contain water in a state of intimate combination, one 

 equivalent at least of it appearing to be inseparable from the 

 salt, and they have a formula analogous to that of hydrated ni- 

 tric acid, or the nitrate of water itself. The nitric acid of sp. 

 gr. 1 .42 appears to be the proper nitrate of water, and of the 

 four atoms of water which it contains, one is combined with 

 the acid as base, and may be named basic water, while the other 

 three are in combination with the nitrate of water, and may be 

 termed the constitutional water of that salt. The same three 

 atoms of constitutional water are found in all the magnesian ni- 

 trates, with the addition often of another three atoms of water, 

 as appears from the following formulae : 



Nitric acid, 1.42. . . . HO,NO 5 + 3HO 

 Prismatic nitrate of copper. . CuO, NO 5 -f3HO 

 Rhomboidal nitrate of copper. . CuO, NO 5 + 3HO+3HO 

 Nitrate of magnesia. . . MgO, NO 5 + 3HO + 3HO 



The proportion of water in the nitrate of magnesia may be re- 

 duced, by heating the salt, to one atom, leaving the compound 

 MgO,NO 5 + HO; but on urging the temperature still higher, 

 the last atom of water and the acid are expelled together, and 

 magnesia is left behind, neither this nor any other nitrate of the 

 magnesian class being capable of existing without an atom of 

 water. The nitrates of the potash and magnesian classes do not 

 combine together, and no double nitrates are known, nor ni- 

 trates with excess of acid. The nitrates with excess of metallic 

 oxide, which are called subnitrates, appear to be formed on the 

 type of the magnesian class : the subnitrate of copper, being 

 HO, NO 5 4- 3CuO, or nitrate of water with three atoms of 

 constitutional oxide of copper ; while the nitrate of red oxide of 

 mercury is HgO, NO 5 -f- HgO, or it resembles the nitrate of 

 magnesia which has been strongly dried, MgO, NO 5 -|-HO. 

 (Kane.) 



