the Heat of Combustion of Organic Compounds. 197 



a series o£ values to estimate relative differences ; for this 

 purpose the figure has been drawn, having for ordinates the 

 measured heats of combustion, and for abscissse the oxygen 

 atoms required in each case. 



1400 



£jl300 



1200 



:ll 00 



1000 



800 



IS 



^ 700 



600 

 500 

 4O0 

 300 

 200 

 J 00 































































- 





















































































• 



i 























> 



A 























> V 



A 























;* 



Y 























*v 



*• 























*y 



























r 



i 























/ 

























A 

























2 4 6 8 10 12 14 16 18 20 22 24 26 



NUMBER Or OXYGEN ATOMS rOR COMPLETE COMBUSTION 



or one molecule; or gas. 



Many of the points overlap ; there are in all 121. A 

 straight line drawn from the farthest point to zero passes 

 through them so closely that 55 touch it. The heat of com- 

 bustion is therefore as a first approximation proportional to 

 the number of oxygen atoms which combine with a molecule 

 of combustible gas, irrespective of molecular complexity and 

 of whether it is carbon or hydrogen that is burnt, and is 

 found to be equal to 53n large calories per gram molecule. 

 This can scarcely be accidental; it has the appearance of 

 representing a general action. What it suggests as the 

 essential feature of combustion is that oxygen is first sensi- 

 tized by contact with the source of ignition and becomes an 

 immensely active agent, atoms of which are able to seize 

 upon and tear apart the almost unresisting hydrocarbon 

 molecule. The heat of the reaction, being all translational 



