542 PROCEEDINGS OF THE AMERICAN ACADEMY. 



The following table gives the specific heats obtained from the series of 

 methylene hydrocarbons : 



It appears from these results that there is a uniform decrease in specific 

 heat with increase in molecular weight. Furthermore the normal hydro- 

 carbons, such as heptane, C 7 H 16 , B. P. 98°, and decaue, C 10 H 22 , B. P. 

 172°, have higher specific heats than their isomers, such for example as 

 isoheptane, C 7 H 1G , B. P. 91°, and isodecaue, C 10 II 22 B. P. 162°. 



The same variation also appears in the methylene series, with high 

 values for certain members that probably indicate different structural 

 relations. 



It is further interesting to observe the materially lower values given 

 by the methylene hydrocarbons as compared with the values for the 

 parafnne hydrocarbons. Whether this be due to greater compactness 

 in the methylene molecule or to some quality of its ring structure, it 

 would be interesting to ascertain. 



Perhaps the falling off in specific heat with increasing molecular 

 weight will appear to better advantage when arranged as ordinates on 

 a curve with the molecular weights as abscissae. Only those compounds 

 are given on the curve that are known to be normal, although, of course, 

 this is not known with reference to the higher members. The different 

 values of the isomers heptane and decane is shown on the shorter curve. 



This uniform decrease in specific heat with increasing molecular 

 weight in the series C n H 2n+ . 2 , suggest a constant relation analogous to 

 the law of Neumann. 



If the constant K be expressed in terms of the specific heat multiplied 

 by the molecular weight and the product divided by the number of atoms 

 in the molecule, the specific heats found for the hydrocarbons of this series 

 give the following values for the constant : 



