408 Mr. R. A. Lehfeldt on the 



Now from equation (19) we have 



log 7r B /7r A = (1 -r) log -g -log k. 



Introducing the numbers for benzene and carbon disulphide, 

 we find 



log7r B /7r A =-5211. 



(v.) New Experiments. 



In order to test the theory developed in the foregoing 

 sections, and especially the accuracy of the expression adopted 

 for the relation of the composition of the vapour to that of 

 the liquid, experiments were undertaken. The mixtures 

 chosen were of benzene with ethyl acetate and benzene with 

 methyl acetate, as those three liquids can be obtained with 

 ease in a reasonably pure state, and their physical properties 

 — such as vapour-pressure and vapour-density — show no 

 abnormalities. The constituents of the first pair have nearly 

 the same vapour-pressure, so that their mixture is well adapted 

 to show the phenomena attending the existence of the maxi- 

 mum of the curve connecting vapour-pressure with compo- 

 sition : while benzene and methyl acetate, on the other hand, 

 have widely different boiling-points, and a corresponding 

 wide difference between the composition of the liquid mixture 

 and its vapour. 



The method adopted for measuring the relation between 

 the compositions (relation between q and t) was one of dis- 

 tillation. The apparatus, which presented no very noteworthy 

 features, consisted of (a) a distillation-flask of about 100 cub. 

 centim., its neck closed by a rubber stopper, through which a 

 thermometer passed ; this was heated in a large water-bath ; 

 (b) a smaller distillation-flask with its neck fitted over the 

 side-tube of (a) ; its bulb was immersed in a mixture of ice 

 and salt ; (c) a water-pump leading through a gauge and 

 large air-chamber to the side-tube of (b). 



In carrying out an experiment, the bath was heated to 

 about 52° or 53°, and kept at that by a thermostat (of 

 Ostwald's usual type) attached to it, so that the liquid in the 

 flask might distil over slowly as near to 50° as possible. The 

 pressure in the air-chamber (but not in the flask and receiver) 

 was then reduced sufficiently; its connexion with the pump 

 closed by a screw pinchcock, and that with the flask and 

 receiver opened. In this way the pressure on the liquid was 

 reduced at once to the amount required, and all the distillate 

 came over at practically the same temperature. On reducing 



