280 PRINCIPLES OF CHEMISTRY 



and nitrogen peroxide, 2NO + O=N 2 O 3 , 2NO + O 2 =2NO. 2 . If nitric 

 oxide is mixed with oxygen and immediately shaken up with caustic 

 potash, it is almost entirely converted into potassium nitrite, whilst 

 after a certain time, when the formation of nitric peroxide has already 

 commenced, a mixture of potassium nitrite and nitrate is obtained. If 

 oxygen is passed into a bell jar tilled with nitric oxide, then brown 

 fumes of nitrous anhydride and nitric peroxide are formed, which in the 

 presence of water give, as we already know, nitric acid and nitric 

 oxide, so that in the presence of an excess of water and oxygen the 

 whole of the nitric oxide is easily and directly converted into nitric 

 acid. This reaction of the re-formation of nitric acid from nitric oxide, 

 air, and water, 2NO + H 2 O + O 3 = 2HNO 3 , is frequently made use of in 

 practice. The experiment showing the conversion of nitric oxide into 

 nitric acid is very striking and instructive. As the intermixture of the 

 oxygen with the oxide of nitrogen proceeds, the nitric acid formed dis- 

 solves in water, and if an excess of oxygen has not been added the 

 whole of the gas (nitric oxide), being converted into HNO 3 , is 

 absorbed, and the water entirely fills the bell jar previously containing 

 the gas. 60 It is evident that nitric oxide 61 in combining with oxygen 



40 This transformation of the permanent gases nitric oxide and oxygen into liquid 

 nitric acid in the presence of water, and with the evolution of heat, presents a most 

 striking instance of liquefaction produced by the action of chemical forces. They per- 

 form with ease the work which physical (cooling) and mechanical (pressure) forces do 

 with difficulty. In this the motion, which is so clearly the property of the gaseous mole- 

 cules, is extinguished. In other cases of chemical action its appearance arises from 

 latent energy that is, in all probability, from the movement of the atoms in the molecules. 



61 Nitric oxide is capable of entering into many characteristic combinations ; 

 it is absorbed by the solutions of many acids (for instance, tartaric, acetic, phos- 

 phoric, sulphuric), and also by the solutions of many salts, especially those formed by 

 suboxide of iron (for instance, ferrous sulphate). In this case a brown compound 

 is formed which is exceedingly unstable, like all the analogous compounds of 

 nitric oxide. The amount of nitric oxide combined in this manner is in atomic pro- 

 portion with the amount of the substance taken ; thus ferrous sulphate, FeSO4, 

 absorbs it in the proportion of NO to 2FeSO 4 . Ammonia is obtained by the action of 

 a caustic alkali on the resultant compound, because the oxygen of the nitric oxide and 

 water are transferred to the ferrous oxide, forming ferric oxide, whilst the nitrogen 

 combines with the hydrogen of the water. According to the investigations of Gay 

 (1885), the compound is formed with the evolution of a large quantity of heat, and is 

 easily dissociated, like a solution of ammonia in water. This subject must be regarded 

 as not sufficiently studied. On passing nitric oxide through nitric acid, nitrogen per- 

 oxide and nitrous anhydride are formed, whose solutions in the nitric acid are, as we 

 have already mentioned, of various colours. It is evident that oxidising substances (for 

 example, potassium permanganate, KMnO 4 , Note 57) are able to convert it into nitric- 

 acid. If the presence of a radicle NO.,,, composed like nitrogen peroxide, must be recog- 

 nised in the compounds of nitric acid, then a radicle NO, having the composition of 

 nitric oxide, may be admitted in the compounds of nitrous acid. The compounds in 

 which the radicle NO is recognised are called nitroso-compoiinds. The compounds are 

 described in Prof. Bunge's work (Kief, 1868). 



