the Constitution of Carbon Compounds. 105 



atomic carbon : the value thus calculated is less than v 2 , but 

 greater than v v 



(26) As regards Thomsen's conclusion that v 1 = v 2 — in 

 other words, that there is no such thing as a double bond, it 

 is to be remarked also that no great confidence can be placed 

 in the determination of the value of v 2 . involving as it does 

 the use of the heat of combustion of carbon monoxide. More- 

 over it cannot be assumed, as a matter of course, that if a 

 compound C 2 2 did exist (§4), it would be strictly speaking 

 an analogue of C 2 H 4 ; i. e. that the energy of combination of 

 two carbon atoms would be the same in the two cases, whether 

 they were associated with oxygen or hydrogen — this, in fact, 

 is the point to be proved. The non-existence of a compound 

 C 2 2 may even be regarded as disproving any such conclusion. 

 The agreement between theory and practice, i. e. between the 

 calculated and observed heats of formation of defines, might 

 be claimed on behalf of Thomsen ; but the amount of evidence 

 of this kind is too small at present, added to which marked 

 discrepancies actually do occur among olefine derivatives — 

 as in the case of the allyl compounds, to which attention has 

 already been more than once directed. 



(27) Finally, another argument against the correctness of 

 Thomsen's conclusions may be based upon the values which 

 he has put forward (it is right to say, with reservation) as 

 representing the affinities of certain elementary atoms, viz.: — 



C . C = 14200 units 

 N.N = 13020 ,. 

 O, 0=2.13970 „ 

 I.I =2.13160 „ 



Except in the case of carbon, these values are supposed to 

 be the amounts of heat developed in the formation of the 

 molecules from the atoms. In the case of carbon, as pointed 

 out in § 7, Thomsen considers it probable that the atoms in 

 the molecule are united in such a manner that at most tw T o 

 affinities are exerted per atom : so that of 38380 units — being 

 the difference between the heat of combustion of ordinary 

 amorphous carbon and the hypothetical heat of combustion 

 of gaseous atomic carbon — 2.14200 units are required to sepa- 

 rate the carbon atoms from each other ; the remaining 9980 

 units are supposed to be absorbed in gasifying the carbon. 

 But if we take into account the properties of the four elements 

 in question, it is inconceivable that the numbers given by 

 Thomsen can represent the amounts of energy to be expended 

 in effecting their molecular simplification. Iodine we know, 

 from V. Meyer's experiments, and from those of Meier and 



Phil. Mag. S. 5. Vol. 23. No. 141. Feb. 1887. I 



