498 Mr. A. Liversidge on Supersaturated Saline Solutions. [June 20, 



/3. That the sudden crystallization is due to some unknown catalytic 

 force. Advocated by Lowell in 1850, but since disproved. 



y. That it is due to the entrance of a particle of the same salt. This 

 explanation is favoured by the majority of the writers upon the question, 

 such as Ziz in 1809, Gernez in 1851, Violettein 1860, Dubrunfautin 1869, 

 by Lecoy de Boisdandran, and others. 



d. That crystallization is due to the presence of fatty, oily, greasy, or 

 other matters in the form of thin films. This theory was propounded by 

 Mr. Tomlinson in two papers* read before the Royal Society, in which 

 also it is stated that certain liquids, such as absolute alcohol, act as nuclei 

 in determining the solidification of such solutions by separating water from 

 the solution, whereas the thin film, on the contrary, owes its activity to 

 the greater attraction which it has for the salt held in solution. 



Preparation of the Supersaturated Saline Solution, 



A little water is placed in the flask, boiled, and sodic sulphate added to 

 the boiling liquid until it ceases to dissolve any more and a deposit of the 

 anhydrous salt begins to take place ; the solution is then filtered and trans- 

 ferred to smaller flasks, usually of about 2 oz. capacity ; these are then 

 again boiled up after being covered with a small beaker, watch-glass, or 

 plugged with cotton- wool. By this method any nuclei adhering to the 

 watch-glass, beaker, or wool are rendered inactive, even should they fall into 

 the solution. 



The solutions are always used of such a degree of supersaturation that 

 crystals of the anhydrous salt are deposited during the boiling. 



Do some liquids, such as alcohol, act as nuclei by combining with a portion 

 of the water of the solution and liberating a little salt which acts as 



a nucleus ? 



Exp. Supersaturated solutions of sodic sulphate were prepared, in the 

 manner described, in 2-oz. flasks, which were closed with a plug of cotton- 



wool through which a bulb-tube was passed, of tne form figuredf, con- 

 taining absolute alcohol. 



* Phil. Trans, vol. cJ riii. pt. ii. and vol. clxi. pt, i. 



t The loop was made in the tube at a so as to prevent any fluid from escaping until 



required. 



