Properties of Liquid Mixtures. 51 



Composition of the Vapour over Liquid-Mixtures. 



The method used was essentially the s:une as that described 

 in the previous paper, to distil a little of a mixture and 

 analyse the distillate. The apparatus was, however, arranged 

 so that the distillate could be drawn off by a tap as required ; 

 it is shown in fig. 3. It consisted of a boiling-tube, fitted 



Fisr. 3. 



and heated as before ; but with the delivery-tube E E bent 

 round to a condenser F. The condenser was provided with a 

 tap G for drawing off the distillate, and a tube which con- 

 nected to the pressure-gauge, reservoir, and air-pump arranged 

 as before. The condenser was designed so as to permit of 

 the use of a freezing-mixture in the bell-jar J by which it 

 was surrounded ; a good many experiments showed, however, 

 that it made no difference to the result whether ice and salt 

 or only cold water was used in J ; so water was used for 

 greater convenience. To make the apparatus air-tight, a 

 crucible full of mercury was placed round Gr, since obviously 

 it was not permissible to lubricate that tap. It is essential to 

 the success of the experiment that no back-condensation 

 should occur, but that the vapour should be collected exactly 

 in the condition it is produced ; so the delivery-tube before 

 the bend must be at least 50°, if the evaporation is taking- 

 place at that temperature. This condition was secured by a 

 very simple device : an incandescent lamp with the ordinary 

 conical shade was lowered as close as possible over the water- 

 bath, and a cloth hung round the whole ; the electrical 



E 2 



