Mr Rudge, On the Specific Heat of Gases, etc. 
85 
On the Specific Heat of Gases at constant volume and high 
pressure. By W. A. Douglas Rudge, M.A., St John’s College. 
[ Read 12 November 1906.] 
Few determinations have been made of the specific heat of 
gases at constant volume, and when such have been made the 
amount of gas used has been small. Joly, using his steam calori- 
meter, employed copper spheres 6'7 cm. in diameter, holding 4 — 5 
grams of the gas. The author has been engaged for some time 
experimenting on the subject, and has obtained results which 
differ somewhat from those previously obtained. The carbonic 
acid used was that sold commercially in the small bulbs, or 
“ sparklets,” used for aerating water. A considerable mass of gas 
can thus be obtained in a small space. The gas is present in the 
liquid state, but on heating to 32° the liquid becomes converted 
into a gas, which is now at the very high pressure of 400 to 500 
atmospheres. Attempts were made at first to determine the 
specific heat in the steam calorimeter after Joly’s plan, but as the 
bulbs sometimes burst the method was abandoned. 
Another plan was then adopted, which, after some modifica- 
tions, took the following form : — A small calorimeter of copper, 
having a light framework arranged in it to hold the bulbs, was 
made. The frame was attached to a spindle which passed through 
the calorimeter cover, and was capable of being rotated by a small 
electromotor. As the experiments were made at fairly high tem- 
peratures, it was necessary to keep the calorimeter closely covered 
in order to prevent loss of water by evaporation. In making the 
experiments the bulbs were placed in position in the calorimeter 
and sufficient water added to cover them. The calorimeter was 
then heated to a temperature a few degrees higher than that at 
which the experiment was to begin. The whole apparatus was 
weighed and then placed in a felt-lined case, and the bulbs set in 
rotation. The temperature was taken by a thermometer passing 
through the lid of the calorimeter, and when it had fallen to a 
certain point, cold water was run in from a burette, and, after 
a few minutes rotation, the temperature of the mixture was 
noted. The calorimeter and its contents were quickly weighed 
and the weight of water added thus found. From the rise in 
temperature of the added water, the amount of heat lost by the 
calorimeter and the gas could be found, and, the heat capacity of 
everything but the gas being known, that of the latter could thus 
be easily calculated. 
