288 PRINCIPLES OF CHEMISTRY 



method of the analysis of the oxides of nitrogen (by passing them over 

 red-hot copper or sodium). In contradistinction to the other oxides of 

 nitrogen, it is not directly oxidised by oxygen, but it may be obtained 

 from the higher oxides of nitrogen by the action of certain deoxidising 

 substances ; thus, for example, a mixture of two volumes of nitric 

 oxide and one volume of sulphurous anhydride if left in contact with 

 water and spongy platinum is converted into sulphuric acid and 

 nitrous oxide, 1>NO + SO, + H,O=H,SO 4 + N 2 O. Nitric acid, also, 

 under the action of certain metals for instance, of zinc fi8 gives nitrous 

 oxide, although in this case mixed with nitric oxide. The usual method 

 of preparing nitrous oxide consists in the decomposition of ammonium 

 nitrate by the aid of heat, because in this case only water and nitrous 

 oxide are formed, NH 4 N0 3 = 2H 2 O + N 2 O (a mixture of NH 4 C1 and 

 KNO 3 is sometimes taken). The decomposition G(J proceeds very easily 

 in an apparatus like that used for the preparation of ammonia or 

 oxygen that is, in a retort or flask with a gas-conducting tube. The 

 decomposition must, however, be carried on carefully, as otherwise 

 nitrogen is formed from the decomposition of the nitrous oxide. 70 



Nitrous oxide is not a permanent gas (absolute boiling point + 36), 

 it is easily liquefied by the action of cold under a high pressure ; at 

 15 it may be liquefied by a pressure of about 40 atmospheres. This 

 gas is usually liquefied by means of the force pump 71 shown in fig. 51. 



metals platinum and silver from their solutions. With mercuric oxide it explodes. It 

 reacts directly with the aldehydes HO, forming N 2 R 2 and water ; for example, with lien/- 

 aldehyde it gives the very stable insoluble benzalazine (CgHsCHN).?, of a yellow colour. 

 Further research should explain the relation of these very interesting salts to amidogen 

 (N 2 H 4 ) itself, which has not yet been isolated. Amidogen must be regarded as a substance 

 which stands to ammonia in the same relation as hydrogen peroxide stands to water. 

 Water, H(OH), gives, according to the law of substitution, as was clearly to be expected. 

 (OH)(OH) that is, peroxide of hydrogen is the free radicle of water (hydroxyli. So also 

 ammonia, H(NH 2 ), forms hydrazine, (NH 2 )(NH 2 ) that is, the free radicle of ammonia, 

 NH 2 , or amidogen. In the case of phosphorus a similar substance, us we shall after- 

 wards see, has long been known under the name of liquid phosphuretted hydrogen, P ,H j. 



68 It is remarkable that electro-deposited copper shavings give nitrous oxide with a 

 10 p.c. solution of nitric acid, whilst ordinary copper gives nitric oxide. It is here 

 evident that the physical and mechanical structure of the substance effects the course of 

 the reaction that is to say, it is a case of contact. 



69 This decomposition is accompanied by the evolution of about 25000 calories per 

 molecular quantity NH^NOs, and therefore takes place with ease, and sometimes with 

 an explosion. 



70 In order to remove any nitric oxide that might be present, the gas obtained is 

 passed through a solution of ferrous sulphate. As nitrous oxide is very soluble in cold 

 water (at 100 volumes of water dissolve 130 volumes of N 2 O, at 20, 67 volumes), it 

 must be collected over warm water. The nitrous oxide is much more soluble than nitric- 

 oxide, which is in agreement with the fact that the nitrous oxide is much more easily 

 liquefied than the nitric oxide. 



71 Faraday obtained liquid nitrous oxide by the same method as liquid ammonia, 



