44 ART. 10. — K. IKEDA : STUDIES ON THE 



relation must hold, and the temperatures at wliicli the liquids 

 have an equal vapour pressure must be proportional to the ab- 

 solute temperature of the boiling points. This has been found 

 to be the case approximately for a great many unassociated 

 liquids. Hence the vapour pressure curves of these liquids do 

 not intersect one another, at least at pressures below 1000 m.m. 

 of mercury. On the other hand the vapour pressure curves of 

 associated liquids mostly intersect those of the normal liquids, and 

 indeed they are at the points of intersection generally steeper 

 than the normal curves. If the heat of evaporation of a normal 

 liquid under the pressure P be q, then in most cases 



^ V — (v — 1)6« ^ 



But as a consequence of Teouton's law 



?a < q- 



l — C 

 Hence in many cases -, — -," ^, D must have considerable value. 



In other words, the heat of dissociation must be considerable. 



As an illustration of what has been said in the foregoing 

 paragraphs we may adduce the vapour tension of acetone. As 

 will be shown in § 2 [b) it is possible to determine the value 

 of V and 9, from the vapour pressure of binary mixtures which 

 consist of a normal liquid and the associated liquid under con- 

 sideration. From the data of Cunaeus at 0°C, it has been 

 concluded that v = 3 and -^ = 162 m.m. As the vapour density 

 of acetone is normal tt^ must be very small, so that equation (29) 

 may be applied. The vapour pressure of acetone at 0° is 

 F = 69.6 m.m. from which we get ^ = 0.1495. The hypothetical 

 vapour pressure of pure simple acetone at various temperatures 

 can be represented by 



