COMPOUNDS OF NITROGEN WITH HYDROGEN AND OXYGEN 267 



of entering into double decompositions, and owing to the volatility 

 of nitric acid, they, like cubic nitre, evolve nitric acid when heated 

 with sulphuric acid. They all, like nitric acid itself, are capable of 

 evolving oxygen when heated, and consequently of acting like oxidising 

 substances, and therefore, for instance, deflagrate with ignited carbon, 

 the carbon burning at the expense of the oxygen of the salt and forming 

 gaseous products of combustion. 36 



Nitric acid also enters into double decompositions with a number 

 of hydrocarbons not in any way possessing alkaline characters and not 

 reacting with other acids. Under these circumstances, the nitric acid 

 gives water and a new substance termed a nitro-compound. The 

 chemical character of the nitro-compound is the same as that of the 

 original substance ; for example, if an indifferent substance be taken, 

 then the nitro-coinpouiid obtained from it will also be indifferent ; 

 if an acid be taken, then an acid is obtained also. Benzene, 

 C 6 H 6 , for instance, acts according to the equation C 6 H 6 + HNO 3 

 =H 2 O + C 6 H 5 NO 2 . Nitrobenzene is produced. The substance taken, 

 C G H G , is a liquid hydrocarbon having a faint tarry smell, boiling at 80, 

 and lighter than water ; by the action of nitric acid nitrobenzene is 

 obtained, which is a substance boiling at about 210, heavier than 

 water, and having an almond-like odour ; it is employed in large 

 quantities for the preparation of aniline and aniline dyes. 37 As 

 they contain both combustible elements (hydrogen and carbon), as 



lead, &c., for hydrochloric acid the salts of silver, &c., are insoluble in water. How- 

 ever, the normal salts of acetic and certain other acids are all soluble. 



111 Ammonium nitrate, NH 4 NO 3 , is easily obtained by adding a solution of am- 

 monia or of ammonium carbonate to nitric acid until it becomes neutral. On evapo- 

 rating this solution crystals of the salt are formed which contain no water of crystallisation. 

 It crystallises in prisms like those formed by common nitre, and has a refreshing taste ; 

 100 parts of water at t dissolve 54 + 0'61 parts by weight of the salt. It is soluble in 

 alcohol, melts at 160, and is decomposed at about 180, forming water and nitrous oxide, 

 NH 4 NO 3 = 2H.>O + N.>O. If ammonium nitrate be mixed with sulphuric acid, and the 

 mixture be heated at about the boiling point of water, then nitric acid is evolved, and 

 ammonium hydrogen sulphate remains in solution ; but if the mixture be heated rapidly 

 to 1()0, then nitrous oxide is evolved. In the first case the sulphuric acid takes up 

 ammonia, and in the second place water. Ammonium nitrate is employed in practice for 

 the artificial production of cold, because in dissolving in water it lowers the temperature 

 very considerably. For this purpose it is best to take equal parts by weight of the salt 

 and water. The salt must first be reduced to a powder and then rapidly stirred up in 

 the water, when the temperature will fall from + 15 to 10, so that the water freezes. 



Ammonium nitrate absorbs ammonia, with which it forms unstable compounds 

 resembling compounds containing water of crystallisation. At 10 NH 4 NO 3 ,2NH 3 is 

 formed : it is a liquid of sp. gr. 1'50, which loses all its ammonia under the influence of heat. 

 At -f 28 NH 4 NO 3 ,NH 5 is formed : it is a solid which easily parts with its ammonia when 

 heated, especially in solution. 



~ 7 The action of nitric acid on cellulose, C 6 H 10 O 5 , is similar. This substance, which 

 forms the outer coating of all plant cells, occurs in an almost pure state in cotton, in 



