VI. On the specific heats of air and carbon dioxide at atmospheric pressure by the continuous electric method at 20˚ C. and 100˚ C

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Abstract
The first reliable investigation of the specific heats of gases was made by Regnault, who in an elaborate series of experiments measured the specific heats of several gases at constant pressure by the method of mixtures. This method, which in modified forms has been employed by nearly all subsequent observers, presents great difficulties when applied to gases, and further, it only gives the mean values of the specific heats over large ranges of temperature, and it is consequently not well adapted to the detection of small variations of the specific heat with temperature. During the period in which I was at the Royal College of Science, London, Prof. Callendar suggested that I should make some measurements of the specific heats of air and carbon dioxide by the continuous electric method, which is particularly well adapted to the measurements of specific heats over small ranges of temperature. I should like to take this opportunity of expressing my deepest thanks to Prof. Callendar for his advice and encouragement throughout the work. (2) Outline o f the Method .—A constant stream of gas is passed through a tube G F, fig. 1, to be presently described, into a jacket J, which surrounds a central tube AB. The gas passes into the tube AB at the temperature of the jacket, and is there heated by an electric current passing through a platinum coil P, the rise in temperature being measured by two platinum thermometers, K and H, used differentially. If C is the electric current, E the potential difference between the ends of the heating coil, Q the mass of gas which flows through the apparatus per second, δ θ the rise in temperature of the gas, J the mechanical equivalent of heat, and S the specific heat of the gas at constant pressure, then neglecting for the present the heating effect of the leads of the heating coil, we have, when the temperature conditions of the different parts of the apparatus have become steady,

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