VII. — On some Lecture Experiments illustrating Proper- 

 ties OF Saline Solutions. — By Prof. J. G. Macgregor, 



Dalhousie College, Halifax, N. S. 



[Received May Ut, ISOL] 



(1.) Ill a paper printed in the last volume of this Institute's 

 Proceedings,* I pointed out that, according to Kohlrausch's obser- 

 vations, sufficiently dilute solutions of sodium hydroxide have 

 volumes which are less than the volumes which their solvent 

 water would have in the free state, one gramme of a solution 

 containing about six per cent, of the hydroxide, having a volume 

 0.0045 cu. cm. less than the water it contains. Several other 

 substances are known which exhibit the phenomenon of contrac- 

 tion on solution, in a similarly marked manner, but none which 

 exhiljit it to such an extent. This hydroxide, therefore, affords 

 the best means of exhibiting the phenomenon of contraction by 

 a lecture experiment. 



The simplest mode of conducting the experiment is to pass the 

 powdered caustic soda, little by little, down a glass tube forming 

 a prolongation of the neck of a large bottle, the bottle and part of 

 the tube having been first tilled with distilled (or, indeed, undis- 

 tilled) water. The substance is quickly dissolved by the water? 

 the strong solution thus formed sinks and mixes with the water 

 below, and the change of volume of the liquid is indicated by the 

 change of height of the column of liquid in the tulje. In order 

 that the experiment may be made quickly, the powder must not 

 be allowed to form a cake in the tube where it meets the water. 

 To avoid this, a tube of about seven or eight mm. diameter must 

 be used. It should be several inches in length, and should have 

 the upper end opened out to a funnel shape, to facilitate the in- 

 troduction of the powder. The tube l)eing necessarily of large 

 bore, the bottle must also be large, so that a small change of 



* Pioc. and Trans. N. S. Inst. Nat. Sci., Vol. VII. (1889), p. 368. 



(71) 



