188 



Mr. W. W. J. Nicol on the Molecular 



the whole apparatus is filled. It is then placed in the con- 

 stant-temperature bath, and after some time (30 minutes) the 

 paraffin is drawn off to mark F, as in other cases. After 

 drying and cooling the whole is weighed; this gives the total 

 weight before mixture. Then by suction at E the contents 

 of B are transferred in great measure to A, and mixture is 

 effected by shaking. The apparatus is then again filled up 

 with paraffin ; brought to a constant temperature, dried and 

 weighed = total weight after mixture. The difference between 

 the last two weights gives the volume-change in grams of 

 paraffin of a known density. In this way the volume-change 

 on mixture of even dilute solutions can be determined with 

 considerable exactness. 



Latterly I employed the apparatus shown in fig. 2, which is 

 Fi£. % 



D (f 



A 



X*J 



more easily used, but requires the aid of a professional glass- 

 blower in its construction. It, too, consists of two tubes, A 

 and B, which are joined by the capillary C. E and D are 

 capillaries ground into A and B respectively. The bend C is 

 filled with mercury, the liquid in excess introduced into B, 

 and the whole weighed. The other liquid is placed in A and 

 it is again weighed ; A and B are then filled up with paraffin, 

 and the capillary stoppers inserted, not to be moved till the 

 experiment is completed. The remainder of the operation is 

 the same as before, mixture being effected by drawing the 

 liquids b; ckwards and forwards through C. Bather better 

 results were obtained with this form of apparatus, owing to 

 the possi^e slight loss on inversion being avoided. 



The advantage of the above method of experiment lies in 

 the fact tl at only one solution of exact compositign is required; 

 and if this be employed for all the determinations; any error in 



