Atomic Laws of Thermochemistry. 35 



to which we may add (C solid) = —38*4. This negative value 

 of (C solid) is well worth notice ; if we wished to get (C), that 

 is the value of that part of the heat-effect of a gramme-atom 

 of gaseous carbon passing into combination which is inde- 

 pendent of the elements it is combining with, we must add 

 the latent heat of vaporization of a gramme-atom of carbon. 



If carbon behaved like a metal, then, according to Table I a. 

 of the Introduction, the latent heat of a gramme-atom of carbon 

 would be 32, but in Part I. we multiplied the values given 

 by Table la. by 1*6, so that in harmony with the latent heats 

 adopted for the metals in Part I. we should take the latent heat 

 of the carbon gramme-atom as 51*2. This, therefore, gives a 

 good general explanation for the large negative value of (C 

 solid) ; if 51*2 is added on for latent heat, then (C) becomes 

 positive with a value 13. From the latent heat and density of a 

 metal its melting-point can be calculated by equation (11), but 

 in the case of carbon the fact that the specific heat does not 

 approach a value satisfying Dulong and Petit's law till near 

 a temperature of 1000 u C. precludes our getting a likely 

 value of the melting-point for carbon from these equations ; 

 but if amorphous carbon, with a density 2*4, behaved as a 

 metal the value 32 for latent heat in equation (11) of the 

 Introduction would give a melting-point 1535° absolute ; 

 this is much too low, and suggests that the value adopted for 

 the latent heat of carbon is at any rate not too large. In a 

 general way therefore our value — 38'4 for(C solid) is shown 

 to be in accordance with a general scheme of facts, and there 

 is a probability of our not being far from the truth when we 

 put (C) = 13. 



Some chemists have objected to the possibility of Thomsen's 

 values vi — v 2 = 14, and v 3 = 0, and have implied that the equa- 

 tion v x = v 2 would abolish all distinction between single and 

 double binding, and that the equation v 3 = is tantamount to 

 the assertion that such a thing as a triple binding does not exist. 

 It is obvious that these objections are quite unsound, because 

 we know it to be possible that two different configurations of 

 the same physical system may have the same amounts of 

 energy. One of the main objects of the study of thermo- 

 chemistry is to discover what we call a bond really is, not to 

 dictate on a priori grounds what it should be. Thomsen 

 himself inferred from the equation v Y = v 2 that so-called double 

 bindings are only single bindings, and that compounds 

 involving them ought to be regarded as unsaturated (in the 

 strict sense of the term) . 



Having determined the fundamental constants given above, 

 Thomsen proceeds to discuss the heat of formation of the 



D2 



