XV. On the Ratio of the Specific Heats of Some Compound Cases. 
By J. W. Carstick, M.A., D.Sc., Fellow of Trinity College, Cambridge. 
Communicated by Professor J. J. THomson, F.R.S. 
Received January 25,—Read February 14, 1895. 
§ 1. Introduction. 
THE experiments to be described in the present paper are a continuation of those of 
which I gave an account in the ‘ Phil. Trans.,’ vol. 185, p. 1. 
It is shown there, from experiments on methane, ethane, and propane, and their 
derivatives, that the monohalogen derivatives of any one paraffin have in the gaseous 
state the same ratio of the specitic heats, and that this ratio is the same as that of the 
hydrocarbon itself in two of the three series. Methane proved to be an exception, 
having a higher ratio than its derivatives. 
It seemed to be a matter of some interest to find whether the same was true of 
unsaturated hydrocarbons and their monohalogen derivatives, and also to find the 
effect of introducing more than one halogen atom into the molecule. The aim of most 
of the experiments described below was to get information on these two points. 
It is not necessary to give a detailed account of the apparatus and method of 
procedure, since they were the same as those described in the paper mentioned above. 
Kunpr’s dust-figure apparatus was used for finding the ratie of the wave-lengths of 
sound of a given pitch in air and in the gas under investigation, and the ratio of the 
specific heats was calculated by means of the formula 
y = 1408 X p X (a) (1 + = PO) 
where p is the specific gravity of the gas referred to air, / and /’ the lengths of the 
dust-figures in the gas and in air respectively, and the last factor is the correction for 
the deviation of the gas from Boyur’s Law. 
The vapour density of the gas was found experimentally at several different 
pressures, and from the curve plotted from the results p and the correction factor were 
determined in the way previously described. 
Some of the substances used in this investigation are very difficult to purify, hence 
it is a matter of importance that when v is determined in the way described. the 
24,.9,95 
