198 Prof. W. M. Thornton on the Relation of Oxygen to 



energy, is the result of the speed with which the oxygen 

 atoms rush into combination, and is therefore proportional 

 only to their number. There is much in the general 

 phenomena of ignition to support this view, especially in 

 the sudden changes of inflammability which occur when the 

 ratios of the oxygen atoms to those of combustible gas are 

 whole numbers. It is, however, capable of interpretation 

 in many instances in terms of the regular occurrence of the 

 CH 2 radicle, as suggested by my colleague Dr. J. A. Smyth,, 

 and the most satisfactory agreements are found in such 

 cases. On the other hand, it suggests that the heat of com- 

 bustion of carbon being twice that of hydrogen may not be 

 altogether accidental, but may be an example of this general 

 relation from which the value for CH 2 is itself derived. 



3. An interesting departure from this is found in the 

 nitro-compounds. The complete combustion of nitro-methane 

 CH 3 N0 2 requires only 1J atoms of oxygen numerically, if 

 the oxygen in the molecule is used in its combustion. Its 

 heat of combustion is 180*9, and H/w is here 120*5. So 

 great a ratio is not found in any of the previous compounds. 



The oxygen required to burn the carbon and hydrogen is 

 3J atoms, and if this is taken instead of 1J, H/n = 51*7 

 bringing it into line. This can only mean that the oxygen 

 contained in these compounds takes no part in their com- 

 bustion, owing perhaps to the difficulty of activating it when 

 associated with nitrogen, and that in these cases combustion 

 is all carried out by free oxygen. This opens a question as 

 to the part played by combined oxygen in explosives. 



Table I. 



Oxygen Molecular 



^ j Molecular atoms n for heat of H 



Compound. r , , , , , . — . 



1 formula. complete combustion. n 



combustion. • H. 



Paraffins. 



Methane CH 4 4 211-9 53*0 



Ethane C 2 H G 7 370*4 53*0 



Propane C 3 H 8 10 529*2 52*9 



Butane C 4 H 10 13 087*2 52*9- 



Pentane C 5 H 12 16 847*1 530 



Hexane C 6 H 14 19 999*2 52*2 



Aromatic Hydrocarbons. 



Benzene C fi H G 15 799*3 53*1 



Toluene 7 H, 18 955*7 53*1 



Mesitylene C 9 H 12 24 1282*3 53*5 



Pseudocomene C 9 H 12 24 1281*5 53*5 



