414 Mr. W. M. Hicks on some Effects of Dissociation 

 Table II. (<9 =5000° = 4727° C). 





2y 





p_ 



0. 



x-\-2y 



1+*. 



9 t 

 To 



-273 







1 





- 73 



•0000 



1-0000 





27 



•0017 



1-0008 



1 



127 



•0096 



1-0048 



10048 



227 



•0269 



10136 



1-0136 



327 



•057 



10268 



10260 



527 



•116 



1-0617 



10610 



727 



•182 



1-1003 



1-0994 



1227 



•313 



1-1850 



11841 



1227 



-459 



1-2970 



1-2961 



00 



1 



2 



1-9984 



18. From Table II. we see that at ordinary temperatures 

 the dissociation is very small when O = 5OOO°, even up as 

 high as 700° C; whilst when O = 1OG° or -173° C., the dis- 

 sociation is always large, even down to —200° C. Also the 

 expansibility in the first case between temperatures 0° C. and 

 100° C. varies as much as in the second case between 0° C. and 

 300° C, though when we get to high temperatures the expan- 

 sibility changes more slowly in the first case than in the 

 second. In the second case the expansibility is almost con- 

 stant between 0° C. and 100° C, and even up to 300° changes 

 only slightly. Again, a difference of 10 per cent, in the value 

 of Q in different gases will produce a difference in their ex- 

 pansibilities at ordinary temperatures of '004 when O is small 

 and about —173° C, and of '00065 when O is large and 

 about 4727° C. In other words, if O be -173° C. in one gas 

 and the value of O in the other gas vary to the extent of 10°, 

 the difference in their expansibilities will vary to the extent of 

 •004 ; whilst if in one O be 4727° C. and the value of Q in 

 the other vary to the extent of 500°, the difference in their 

 expansibilities will vary to the extent of '00065. These three 

 reasons, viz. (1) smallness of dissociation, (2) constancy of 

 expansibility, (3) near equality of expansibilities of different 

 gases, lead us to believe that in the case of the permanent gases 

 O is large compared with ordinary temperatures. Still there 

 may be gases whose O is small. It is possible that mercury 

 vapour is such a gas, "and that this accounts for the fact that 

 its molecules are monatomic, viz. that the temperature at 

 which it exists is a large multiple of its O , and that therefore 

 the dissociation is large. 



