68 Prof. W. M. Thornton on the Nature of Chemical 



are both constant, and to the same degree of approximation. 

 According to a gravitational law of attraction or power of 

 acquiring and retaining oxygen, affinity, measured by the 

 product m x m^ should then be proportional to H 2 . Con- 

 versely, when the ratio H 2 /m 1 m 2 is constant, it is strong 

 presumptive evidence that affinity follows this law, whatever 

 the ultimate electromagnetic explanation may be ; but it is 

 only when the products of combustion are of similar com- 

 position in every case, as they are in the examples to be 

 quoted, that heat of combustion can be used to find a law of 

 affinity common to all the compounds examined. 



4. Taking the heats of combustion given by Thomsen 

 ('Thermochemistry,' Tables 35 to 44), the values of YP\m v m 2 

 for the paraffin series, though fairly constant, fall slightly to 

 a steady number as the series rises (Table I.). (B. — 15) 2 lm l m 2 

 is more constant. 



Table I. 







Compound. 



Oxygen. 





H 2 



(H-15) 2 







ffl,. 



m 2 . 



H*. 



m x m 2 



m x m 2 



Methane . . . 



CH 4 



16 



64 



212 



439 



37-9 



Ethane 



C 2 H 6 



30 



112 



370 



40-7 



37-6 



Propane 



C 3 H 8 



44 



162 



529 



397 



37-6 



Butane 



C 4 H 10 



58 



208 



687 



39-2 



37-5 



Pentane 



Q5H12 



72 



256 



847 



391 



37-6 



Hexane 



C 6 H 14 



86 



304 



992 



38-7 



37-6 



Heptane 



7 H ]G 



100 



352 



1166 



38-6 



37-8 



Decane 



ClO H 22 



142 



496 



1645 



38-6 



37-8 



Means... 



39-8 



37-6 



* Kilogram-calories per gram molecule. 



For the other compounds of which the heats of combustion 

 are given by Thomsen the mean values of IF/w^m 2 are as * n 

 Table II. 



Table II. 



Compounds. 



H 2 /ffl 1 m 2 . 



Aromatic hydrocarbons 



345 



38-2 

 35-4 

 36-4 

 35-8 

 34-6 

 34-7 

 39-9 

 38-0 



Unsaturated hydrocarbons 











Esters 









