the Constitution of Carbon Compounds. 95 



were in the original oxygen molecules, heat is absorbed only 

 in the separation of the nitrogen atoms. On the other hand, 

 the heat developed arises from the association of the nitrogen 

 atoms each with two oxygen atoms, as exhibited in the 

 formula above, the expression 4N . signifying merely four 

 single nitrogen -oxygen affinities. On the assumption that 

 N" : = 2N . 0, i. e. that the amount of heat developed when a 

 single atom of nitrogen combines by two of its affinities with 

 a single atom of oxygen is double that to which the associa- 

 tion of an atom of nitrogen by but one of its affinities to an 

 atom of oxygen gives rise, the difference between the heats 

 of formation of nitrogen monoxide and dioxide will be the 

 amount of heat developed in the formation of the oxygen 

 molecule : 



(N 2 , 20 2 =2N0 2 )-(Isr 2 , 2 =2NO)=2 . 13160. 

 /. 0.0 = 26320 units. 



Provided that the heats of formation of nitrogen and oxygen 

 molecules thus deduced be accepted, the heat developed in the 

 formation of nitric oxide from nitrogen and oxygen atoms 

 may also be ascertained, thus : — 



N 2 , 20 2 =2N0 2 = 2(-8415)=4N.O-N.N 



-16830-13020= -3810=4N.O. 



.\N.O= -952 units. 



The value thus deduced is very small, and probably may be 

 regarded as zero, it being unlikely — remarks Thomsen — that 

 there are atoms which exercise a negative affinity. 



(15) Heat of Formation of Cyanides. — Comparing homo- 

 logous cyanides, the difference between the heats of formation 

 of acetonitrile (60500) and propionitrile (104310) is 43810 

 units, or very nearly the value which in other cases corre- 

 sponds to a difference of CH 2 ; but the difference between 

 hydrogen cyanide (10900) and acetonitrile is considerably 

 greater, viz. 49600 units, pointing to a difference in consti- 

 tution between the nitriles and hydrogen cyanide. 



Assuming the formula of acetonitrile to be CH 3 . C : N, 

 the heat of formation of the radical C i N from atomic carbon 

 and ordinary nitrogen will be the difference between the heat 

 of formation of acetonitrile, 60500 units, and Sr + v-i =59200 

 units, *. e, 1300 units. Adding to this half the value N . N 



0:^=1300 + 6510 = 7810 units. 



A similar calculation for propionitrile gives 910 + 6510 = 

 7420 units. 



In like manner, adding 6510 to the heat of formation of 



