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XVII. On the Specific Heats of Gases at Constant Volume .—Part III. The Specific 
Heat of Carhon Dioxide as a, Function of Temperature. , 
By J. JoLY, M.A., Sc.D., F.JR.S. 
Eeceived March 9,—Read April 26, 1894. 
The question of the dependence of the specific heat of carbon dioxide upon its 
density having been investigated, so far as is described in Part II., the further 
question remained over as to whether the specific heat of a gas is dependent upon 
the range of temperature over which the gas is heated. The question was evidently 
wdthin the power of the steam calorimeter to answer, provided arrangements were 
made for varying the lower limit of temperature—the initial temperature. To vary 
the upper limit by resorting to vapours other than steam would, on the large scale 
upon wPich operations w^ere being conducted, have been costly and troublesome, 
although not attended with any inaccuracy, as the experiments of Wirtz^ on the 
Latent Heats of several vapours, determined by the method of condensation, appear 
to show. It is to be observed, indeed, that the use of vapours other than water w^ould 
allow of operations being conducted upon smaller quantities of the gas, as it would be 
easy to find liquids whose vapours possessed a latent heat one-half or one-fourth as 
great as that of water; and a construction necessitating but little loss of vapour at 
each experiment could be easily contrived. In this case, also, it would be necessary 
to provide a means of varying the initial temperature. Chiefly on the grounds of 
expense I decided upon the use of steam in conjunction with a means of altering the 
initial temperature. It appeared probable, too, that the alteration of the initial 
temperature between 10° and 100° would disclose the chief points of interest in the 
case of the gas under consideration, the critical temperature lying within this range. 
A means of altering the initial temperature was obtained by conferring such a form 
upon the steam calorimeter as would permit of the circulation of the vapour of a 
suitable liquid, boiling under atmospheric pressure, around an inner chamber containing 
the active and the idle vessels till these had acquired the temperature of the vapour. 
Steam could then be admitted directly into the inner chamber; the resulting precipi¬ 
tation upon the vessels being that due to the range defined by the boiling-point 
of the liquid and the boiling-point of water. The accompanying figure (from a 
*‘Ueber eine Anwendung des Wasserdampfcalorimeters zur Bestimmung von Yerdampfuugs- 
warmen.’ Karl Wirtz. Leipzig, 1890. 
MDCCCXCIV.—A. 6 G 
28.12.94 
