1895.] 



on Argon. 



535 



but there is no reason to suppose that the density is different, such 

 numbers as 19*7 having been obtained. 



One of the most interesting matters in connection with argon, 

 however, is what is known as the ratio of the specific heats. I must 

 not stay to elaborate the questions involved, but it will be known to 

 many who hear me that the velocity of sound in a gas depends upon 

 the ratio of two specific heats — the specific heat of the gas measured 

 at constant pressure, and the specific heat measured at constant 

 volume. If we know the density of a gas, and also the velocity of 

 sound in it, we are in a position to infer this ratio of specific heats ; 

 and, by means of this method, Professor Ramsay has determined the 

 ratio in the case of argon, arriving at the very remarkable result 

 that the ratio of specific heats is represented by the number J. • 65, 

 approaching very closely to the theoretical limit, 1 • 67. The number 



1IY 



1-67 would indicate that the gas has no energy except energy of 

 translation of its molecules. If there is any other energy than that, 

 it would show itself by this number dropping below 1 ■ 67. Ordinary 

 gases, oxygen, nitrogen, hydrogen, &c, do drop below, giving the 

 number 1*4. Other gases drop lower still. If the ratio of specific 

 heats is 1*65, practically 1*67, we may infer then that the whole 

 energy of motion is translational ; and from that it would seem to 

 follow by arguments which, however, I must not stop to elaborate, 

 that the gas must be of the kind called by chemists monatomic. 



I had intended to say something of the operation of determining 

 the ratio of specific heats, but time will not allow. The result is, no 

 doubt, very awkward. Indeed, I have seen some indications that the 

 anomalous properties of argon are brought as a kind of accusation 

 against us. But we had the very best intentions in the matter. The 

 facts were too much for us ; and all we can do now is to apologise for 

 ourselves and for the gas. 



2 o 2 



