COMPOUNDS OF CAKUoN WITH OXY<-KX AND NITROGEN 399 



cyanouv,'! di-rivatives, and is regarded as the consequence of the above- 

 mentioned explanation of their nature. All cyanogen compounds are 

 .million in in salts, R(CNH 4 O 2 ), deprived of water, 2H._,O ; therefore 

 their molecules ought to show the faculty of combining with two mole- 

 cules of water or with other molecules in exchange for it (for instance, 

 with H 2 S, or HC1, or 2H 2 , c.), and are therefore capable of combining 

 together. The combination of molecules of the same kind to form 

 more complex ones is nothing else but polymerisation. 40 



Besides being a substance very apt to form polymerides, cyanic acid 

 presents many other features of interest, expounded in greater detail 

 in organic chemistry. First of all, the transition of ammonium cyanate 

 into urea ought to be considered. The reason is that the salts of 

 cyanic acid, which are easily split up, by the action of acids and even 

 of water, into ammonia and carbonic anhydride, are produced by the 

 oxidation of saline metals, as we shall see further on. Potassium 

 cyanate, KCNO, for instance, is most often obtained in this way. 

 Solutions of cyanates, by the addition of sulphuric acid, yield 

 cyanic acid, which, however, immediately decomposes : CNHO + H 2 O 

 =CO 2 + NH 3 . A solution of ammonium cyanate, CN(NH 4 )O, behaves, 

 in the same manner, but only in the cold. On being heated it 

 completely changes, because it is transformed into urea. The composi- 

 tion of both substances is identical, CN 2 H 4 O, but the structure or dis- 

 position and the connection between the elements is different : in the 

 ammonium cyanate one atom of nitrogen exists in the form of cyanogen, 

 CN that is, united with carbon and the other as ammonium, NH 4 , 

 but, as cyanic acid contains the hydroxyl radicle of carbonic acid, 

 OH(CN), the ammonium in this salt is united with oxygen ; whilst in 

 urea both the nitrogen atoms are symmetrically and uniformly disposed 

 as regards the radicle CO of carbonic acid : CO(NH 2 ) 2 . For this 

 reason, urea is much more stable than ammonium cyanate, and there- 

 fore the latter, on being slightly heated in solution, is converted into 



40 Just as the aldehydes (for instance, C 2 H 4 O, page 145) are alcohols (for instance, 

 C 2 H 6 O) which have lost hydrogen. 



The aldehydes are also capable of entering into combination with many substances, 

 and of polymerising, forming slightly- volatile polymerides, which depolymerise on heating. 

 Although there are also many similar phenomena (for instance, the transformation of 

 yellow into red phosphorus, the transition of cinnamene into metacinnamene, &c.) of 

 polymerisation, in no other case are they so clearly and simply expressed as in cyanic 

 acid. The details relating to this must be sought for in treatises on organic and 

 theoretical chemistry. If we touch on certain sides of this question it is principally with 

 the view of showing the phenomenon of polymerisation by typical examples (this pheno- 

 menon being met with more frequently than was formerly imagined, see Silica), and 

 also to show the faculty which cyanogen derivatives have of forming the most varied 

 compounds. 



