96 Prof. H. E. Armstrong on the Determination of 



hydrogen cyanide (10900 units), the heat developed in its 

 formation from ordinary hydrogen, gaseous " atomic " carbon 

 and atomic nitrogen will result ; deducting from this 1 5000 

 units on account of the hydrogen, the remainder (17410- 

 18000=2410) will be the amount of heat developed in the 

 formation of the radical ON. It is much lower than that found 

 for either of the nitriles. 



The heat of formation of cyanogen from gaseous atomic 

 carbon and atomic nitrogen is 24080 units. Assuming that 

 it has the constitution N : C . C i N, 



24080 = 2NiO + C.C = 2N:C-f^ 



.-. 2Ni = 24080-14200 = 9880. 



The value for Ni O (4940 units) thus deduced is much lower 

 than was calculated from the heat of formation of the nitriles. 

 If it be assumed that cyanogen has the formula N : C : C : N 

 the value 4940 would be the heat developed in the combina- 

 tion of carbon and nitrogen atoms by double affinities. But 

 more probably, says Thomsen, its constitution is to be repre- 

 sented by the formula O : N . N : C, in which case 



24080 = 2N:C + N.N; 

 whence 



N:C= 5530. 



It would appear, therefore, that the affinity of carbon for 

 nitrogen varies according to the mode of combination, the 

 values obtained being 



From acetonitrile ") "NT * P f 7810 



„ propionitrilej * ' ' iN : ° \ 7420 



„ cyanogen . . . (?)NjC 5530 



„ hydrogen cyanide (?) N . C 2410 



Very probably the three values are related as 3:2:1, and 

 the heat developed on combination of carbon and nitrogen 

 atoms is proportional to the number of affinities satisfied, 

 being on an average 2600 units per affinity. 



(16) Seat of Formation of the Amines. — The difference be- 

 tween the heats of formation of homologous amines is some- 

 what greater than is usually found between homologues, 

 especially in the case of secondary and tertiary amines, but 

 some uncertainty attaches to the values for these latter on 

 account of their high heats of combustion. The heats of 

 formation of primary amines are greater than those of the 

 isomeric secondary and tertiary amines. Thus 



