282 Lord Rayleigh and Prof. Ramsay. [Jan. 31, 



ratio of specific heat at constant pressure to that at constant volume 

 can be deduced by means of the equation 



when n is the frequency, X the wave-length of sound, v its velocity, 

 e the isothermal elasticity, d the density, (1-f #0 the temperature cor- 

 rection, Cp the specific heat at constant pressure, and C that at constant 

 volume. In comparing two gases at the same temperature, each of 

 which obeys Boyle's law with sufficient approximation, and in using 

 the same sound, many of these factors disappear, and the ratio of 

 specific heats of one gas may be deduced from that of the other, if 

 known, by means of the proportion 



\ 2 d:\' z d' :: 1-41 : a, 



where, for example, X and d refer to air, of which the ratio is 1*41, 

 according to observations by Rontgen, Wiillner, Kayser, and Jamin 

 and Richard. 



Two completely different series of observations, one in a tube of 

 about 2 mm. diameter, and one in one of 8 mm., made with entirely 

 different samples of gas, gave, the first, 1'65 as the ratio, and, the 

 second, 1'61. 



Experiments made with the first tube, to test the accuracy of its 

 working, gave for carbon dioxide the ratio 1*276, instead of 1'288, the 

 mean of all previous determinations; and the half wave-length of 

 sound in hydrogen was found to be 73'6, instead of 74'5, the mean of 

 those previously found. The ratio of the specific heats of hydrogen 

 found was V39, instead of 1-402. 



There can be no doubt, therefore, that argon gives practically the 

 ratio of specific heats, viz., 1*66, proper to a gas in which all the 

 energy is translational. The only other gas which has been found to 

 behave similarly is mercury gas, at a high temperature.* 



XV. Attempts to induce Chemical Combination. 



Many attempts to induce argon to combine will be described in full 

 in the complete paper. Suffice it to say here, that all such attempts 

 have as yet proved abortive. Argon does not combine with oxygen 

 in presence of alkali under the influence of the electric discharge, 

 nor with hydrogen in presence of acid or alkali also when sparked ; 

 nor with chlorine, dry or moist, when sparked ; nor with phosphorus 

 at a bright-red heat, nor with sulphur at bright redness. Tellurium 

 may be distilled in a current of the gas ; so may sodium and potas- 

 sium, their metallic lustre remaining unchanged. It is unab- 

 * Kundt and Warburg, < Pogg. Ann.,' vol. 157. p. 353 (1876). 



