on the Phy s leal Properties of Gases. 411 



are two periods when the variation of the proportions is small, 

 viz. when the temperature is small compared with Q (less than 

 ■^-q0 ) and when it is greater than . The curve, of course, 

 has an asymptote at a distance 1 from the origin; if we regard 

 this as the line of abscissas, the ordinates measured from it give 

 the values of r\. 



14. In considering the pressure of the gas we may treat it 

 as a mixture of two. We shall therefore have 



jt9 = § . %nxv\-\-^m . 2yv 



where v i} v 2 are the velocities of mean square in the two cases ; 

 and therefore 2mv* = mvl = \0, where 6 is the absolute tempe- 

 rature and X some constant, whence 



p=§ (*+2t,)x0= | ( g|) xe= |(i+ -L) xe 



If there were no dissociation, we should have, calling P the 

 pressure in this case, 



hence 



P=(i + OP- 



Fig. 2 shows the relations of p and P in a gas where s = %s 2 ; 



Pig-- 2. 



the abscissas represent the temperature, and the ordinates the 

 corresponding pressures in the two cases. The bend in the 

 curve between '50 o and 1'5# is noticeable. 



15. According to the ordinary theory ~P = /cpt, where t is 

 the temperature measured from a certain zero-point, which is 

 very slightly different for the different permanent gases. Ac- 

 cording to the above theory p = /cp(l + £)0, where 6 is the 

 mean kinetic energy of translation of the particles composing 

 the gas. Now, in the formula T = Kpt, the temperatures are 



