32 Mr. W. Sutherland on the Fundamental 



6. Heat of Formation of the Carbon Molecule from its 

 Atoms. — If 135-34 is taken to be the heat of combustion of 

 an isolated carbon atom, and 96*96 that of an atom as it 

 exists in solid amorphous carbon, then 38 '4 is the heat 

 required to vaporize a gramme-atom of solid amorphous 

 carbon and resolve it into atoms; so that if there are n atoms 

 of carbon to the molecule, the heat required to vaporize and 

 dissociate a gramme-molecule of solid amorphous carbon is 

 n x 38*4. According to our mode of expression this reasoning- 

 becomes 



2(0) + 2/(CO a )-2/(CO) = 135-34/ ... (8) 

 2(0)+2/(C0 3 )+(C solid) =96-96; 



/(CO,)-2/(CO)-(Csolid) = 38-38. . . (9) 



therefore 



The symbol (C solid) stands for that part of the change of 

 energy of a gramme-atom passing from the amorphous solid 

 state into a gaseous compound which is independent of the 

 nature of the elements to which the C atom is united. If 

 /(C0 2 ) = 2/(CO), then -(0 solid) =38-4; so that on this 

 assumption the number 38*4 has a different signification from 

 that assigned to it by Thomsen. 



7. Heat of Combination of Carbon with Hydrogen. — The 

 principle on which Thomsen proceeds in the rest of his 

 investigations in vol. iv. of the Thermochemische Unter- 

 suchungen is always to add to the heat of formation of a 

 compound from solid amorphous carbon 38*4 for each atom 

 of carbon, so as to get what he calls the heat of formation 

 from isolated carbon atoms. But it appears from his later 

 writings that he considers it not to be possible from existing 

 data to obtain the heat required to vaporize and dissociate 

 the gramme-molecule of solid amorphous carbon, so that he 

 would appear to allow now that the addition of 38'4 for each 

 carbon atom serves no good end. But we have seen that, 

 with the not unnatural assumption that /(C0 2 ) = 2/(C0), 

 the number 38*4 has the important signification — (C solid), 

 and therefore its addition for each atom of solid carbon taking 

 part in the formation of a compound molecule serves the 

 important purpose of eliminating the function — (C solid) 

 from the expression for the heat of formation : we shall see 

 this purpose illustrated by following Thomsen in this seventh 

 section. The heat of formation of CH 4 from solid carbon 

 and gaseous hydrogen is 21*2; adding 38*4 we get 59*6, 

 which was formerly regarded by Thomsen as the heat of 

 formation of CH 4 from isolated carbon atoms and hydrogen 



