270 



SCIENCE PROGRESS. 



chloride, thionyl chloride, sulphuryl chloride, nickel tetra- 

 carbonyl, etc. 



It has already been pointed out that, in the gas equation 

 pv = RT, the value of R is 0*0819, and that it does not vary 

 with the temperature provided the molecular weight of the 

 gas has been correctly chosen and that no dissociation occurs. 

 If, however, dissociation takes place the value of R in- 

 creases with rise of temperature. As we shall see later on, 

 there is a great deal of evidence to show that the molecules 

 of certain liquids, in passing from the state of vapour to that 

 ol liquid, associate to form more complex molecules, and 

 that these liquids are precisely those which possess an ab- 

 normal and variable value of k. The effect of association 

 would be that the real molecular weight would be chosen 

 too low, and consequently that the value of k would appear 

 to be less than 2*12 1. Furthermore, if such an associated 

 liquid dissociated on heating, the low abnormal value of k 

 would gradually increase. This is, in fact, what actually 

 takes place, and Ebtvbs pointed out that the degree of 

 association or the molecular complexity of the liquid could 

 be calculated on this basis. The following experimental 

 results, for example, have been obtained by Ramsay and 

 Shields : — 



It will be seen that the value of /- differs widely from 

 2*121 and that it gradually increases with rise of tempera- 

 ture. 



The question which now rises is how the degree of 



