104 Specific Heats of Paraffins and Derivatives. [June 15 r 



In the experiments the reservoir was always adjusted so that the 

 level of the mercury in CD stood near the mark at K, thus simpli- 

 fying the calculations a little. 



The apparatus was found to give values of the vapour density 

 concordant to about one part in 1000. 



The formula used in calculating the ratio of the specific heats was 



the last factor being added to the ordinary formula to correct for the 

 divergence of the gas from Boyle's Law. 



The correction is obtained at once by putting in the equation 



i/dp\ XT. /dp\ -L fdpv\ (dp\ 



u~ = 7tr(-~ the value of (~) given by (-] = *>4-t*(~] 



\dvjt \dvjt e J \dvjt * \dvjt 



From the vapour density determinations a curve is constructed 

 giving pv in terms of v, and the slope of this curve at any point gives 



the value of ^ (pv) in arbitrary units. Dividing by the correspond- 



ing value of p in the same units, we obtain the amount of the 

 correction. 



The correction increases the ratio of the specific heats by from 1 to 

 2 per cent, in most cases. 



Observations varying in number from three to nine were made on 

 each gas, the extreme range of the values being 2 per cent, for marsh 

 gas, 1^ per cent, for methyl iodide, and 1 per cent., or less, for the 

 rest. 



The mean values are shown in the following table : 



Methane ................. CH 4 ...... 1-313 



Methyl chloride ........... CH 3 C1 ...... 1*279 



Methyl bromide .......... CH 3 Br ...... ' 1'274 



Methyl iodide ............ CH 3 I ........ 1-286 



Ethane .................. C 2 H 6 ......... 1*182 



Ethyl chloride ............ C 2 H 5 C1 ....... 1-187 



Ethyl bromide ............ C 2 H 5 Br ....... 1-188 



Propane ................. C 3 H 8 ......... 1-130 



Normal propyl chloride .... %C 3 H 7 C1 ....... 1*126 



Isopropyl chloride ........ iC 3 H 7 Cl ....... 1*127 



Isopropyl bromide ........ ^C 3 H 7 Br ...... 1'131 



From this table we have the interesting result that the gases fall 

 into four groups, the members of any one group having within the 

 limits of experimental error the same ratio of the specific heats. 



