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



linked, must, in fact, be regarded as unsaturated; and that this 

 is more especially the case with compounds with so-called triple 

 bonds. For the present it must be left undecided how the 

 carbon atoms are held together in compounds of this last- 

 mentioned class ; their union is certainly unattended with 

 development of heat. This conclusion, Thomsen considers, is 

 in agreement with experience : bodies with " trebly-linked " 

 carbon atoms are in a condition of unstable equilibrium, which 

 is easily disturbed by external influences, and such compounds 

 are easily decomposable ; this could not be the case if the 

 carbon atoms were firmly held together (comp. § 24). 



As the force with which carbon atoms are held together in 

 gaseous compounds — expressed in heat-units — never exceeds 

 about 14200 units, the separation of gaseous diatomic carbon 

 molecules into atoms would involve the absorption of only 

 this amount of heat per gram-atomic proportion. The much 

 greater absorption of heat in converting amorphous into 

 gaseous " atomic " carbon may be explained by assuming that 

 each atom of carbon is combined with several others, that is 

 to say, that the molecule of carbon is complex ; if the mole- 

 cule contain five or more atoms, each atom may be in direct 

 connection with four other atoms : in such a case the number 

 of linkages will be twice the number of atoms, and the heat 

 developed on combination will be 2 . 14200 units per gram- 

 atomic proportion. The difference between this number and 

 38380 units — the amount of heat absorbed in converting 

 ordinary amorphous into gaseous "atomic" carbon — viz. 

 9980 units, will be the amount required to gasify the carbon 

 as distinct from that absorbed in producing molecular dis- 

 ruption. 



(8) Heat of Combustion of Isomeric Hydrocarbons. Con- 

 stitution of Benzene. — From the foregoing explanations it 

 will be evident that the heat developed in the formation of a 

 gaseous hydrocarbon, C a H 2 5, from gaseous atomic carbon and 

 ordinary hydrogen at constant volume, may be expressed by 

 the formula 



{C a ,1I 2b )=2b.r + tv 



= b. 30000 + n. 14200. 



If ordinary amorphous carbon be taken, the formula becomes 



(C«, H 26 ) =b . 30000 + n . 14200-a . 38380 ; 



while the heat of formation under constant pressure may be 

 calculated from the equation 



(C a , H 26 ) = 6. 30000 + ^.14200- a. 38380 +(6-1) 580. 



