3819.] Oxides and Sails of Mercury. 249 



This is the true subnitrate ; it is yellow when it contains more 

 acid, and white when nearly saturated. 



30. When a few drops of an alkaline or earthy solution are 

 mixed with solution of nitrate of mercury, a white powder 

 appears ; if more alkali be added, the white powder becomes 

 grey ; at length dark grey : this is the same subnitrate. Further 

 additions of the alkali take up the whole of the acid, and the 

 oxide is left accoiding to the conditions already detailed (4). 



31. When red oxide of mercury is dissolved in dilute nitric 

 acid, and evaporated to dryness, a white crystalline mass is 

 obtained, which deliquesces, although not to perfect fluidity. 

 This is oxynitrate of mercury. 



The same salt is formed by boiling crystals of nitrate of mer- 

 cury in nitric acid, an effervescence being excited owing to the 

 abstraction of oxygen, or by dissolving mercury in a large quan- 

 tity of nitric acid, and evaporating to dryness. This salt, in a 

 certain quantity, is formed in every case where mercury and nitric 

 acid, of whatever strength, are suffered to act on each other, 

 and remains dissolved after all the nitrate has been separated by 

 crystallization. 



Cold water, unless acidulated, decomposes the oxynitrate into 

 an acidulous soluble portion, and an insoluble brown powder. A 

 stream of sulphuretted hydrogen, passed through this powder, 

 separates nitrous acid, so that this is suboxynitrate. By means 

 of boiling water, Thenard separated the whole of the nitrous 

 acid. 



32. Under ordinary circumstances, if nitric acid be boiled on 

 mercury, and the solution evaporated to dryness, a yellow mass 

 is produced, which has been supposed to be oxynitratf; ; and 

 the yellow powder which may be obtained from it by means of 

 cold water has been stated as suboxynitrate. But this is not so, 

 for the yellow mass is a mixture of nitrate and oxynitra te with 

 their subsalts. When cold water is added, the nitrate affords 

 whitish-yellow subnitrate, the oxynitrate gives reddish-brown 

 suboxynitrate, and the mixture of these produces the yellow 

 powder which has been mistaken for nitrous turbith. If the 

 water be boiling, the subnitrate is still further deprived of its 

 acid, and becomes the blue-grey subsalt, the intermixture of 

 which with the rest gives the greenish tinge. The real, nitrous 

 turbith is red-brown. 



33. It is now necessary to ascertain the constitution of the 

 oxides that form salts by combination with nitric acid. The 

 nitrate and subnitrate evidently contain the same oxide, and 

 when this is separated by means of potash, its analysis is that 

 which has been already stated (13). The same thing is shown 

 synthetically ; for when black oxide is presented to nitric acid, 

 either of these salts is produced according to the dilution, and 

 no gas is evolved. 



That the oxynitrate and suboxynitrate contain the same oxide, 



