Foundations of the Kinetic Theory of Gases. 141 



If a compound of silver with a valency 17 or 19, or one of 

 copper with a valency of 19, were known, this suggestion 

 might become a somewhat plausible hypothesis ; in their 

 absence it must, I fear, be regarded merely as an idle specu- 

 lation. The only reaction of silver that has occurred to me 

 as likely to give any evidence of such a compound is its 

 behaviour with oxygen when melted. I have not, however, 

 been able to find the composition of the compound or mixture 

 given more accurately than by the statement that silver gives 

 out twenty- two times its volume of oxygen when it is nearly at 

 the point of solidification. Taking this rough statement of 

 the composition and assuming values for the density of the 

 silver and oxygen, the formula for the compound works out 

 to be Ag 49 0, which is sufficiently near to AgCK^ to make one 

 wish that the composition were more accurately known. 



It is perhaps merely a remarkable coincidence that, taking 

 the atomic weight of potassium as 394, and that of sodium as 

 23, the ratio of the two gives 



"17" I n 



m = ^ exactly; 



or the same as the ratio of the atomic weights of silver and 

 copper ; and in the absence of more complete certainty in the 

 determinations of atomic weights it may be unwise to speculate 

 about the matter. 



Cavendish Laboratory, 

 December 1886. 



XVII. On the Foundations of the Kinetic Theory of Gases. 

 Part II. By Professor Tait*. 



IN a former paper (of which a brief abstract appeared in 

 the Philosophical Magazine for April 1886, p. 343, and 

 which has since been printed in full in Trans. Koy. Soc. 

 Edin.) I showed that the recovery of the " special " state by 

 a gas supposed to consist of equal hard spheres takes place, at 

 ordinary pressures and temperatures, in a period of the order 

 of 10~ 9 seconds, at highest. 



This forms the indispensable preliminary to the present 

 investigation. For it warrants us in assuming that, except 

 in extreme cases in which the causes tending to disturb the 

 " special " state are at least nearly as rapid and persistent in 



* Abstract of Papers read to the Royal Society of Edinburgh, Decem- 

 ber 6, 1886, and January 7, 1877. Communicated at the instance of Sir 

 W. Thomson. 



