1872.] Mr. A. Liversidge on Svpcrsaturatcd Saline Solutions. 501 



minutes; and although the finger was strongly pressed against the sides 

 of the flask, which was seen to he smeared all over, yet crystallization was 

 not set up when the solution was made to flow over the finger-marks, which 

 were plainly visible. That the solutions were not warmed by the heat of 

 the finger, and so rendered inactive, is proved by their immediately solidi- 

 fying on the insertion of a dirty glass rod. 



Exp. By means of the two modifications of bulb-tube, as already de- 

 scribed for the experiments with absolute alcohol, thin films of various oils 

 and other bodies were formed upon the surface of supersaturated solutions 

 without inducing crystallization. That is, a small glass bulb was filled 

 with the oil or other body and boiled, then supported in the neck of the 

 flask by a plug of cotton ; the supersaturated solution was then boiled and 

 allowed to cool ; when quite cold a drop of the liquid was forced out of the 

 bulb on to the solution, then by a sudden jerk the lens or small globule 

 thus obtained was flattened out into a thin film, often iridescent, but with- 

 out causing solidification. 



In numerous instances the temperature of the solution was lowered by 

 means of ice-cold water, so as to increase its sensitiveness, but with no 

 different result. 



Jn many cases the oil or fatty body, such as olive-oil, Russian tallow, 

 citronella-oil, castor-oil, &c, was dissolved in ether and then used ; this 

 device was used for two reasons : first, so that the greasy matter might be 

 much diluted and so spread over a large surface, and then be left as a 

 thin film on the evaporation of the ether ; and second, so that a much 

 smaller quantity of the oil might be delivered at a time. Usually the oil 

 collected into globules shortly after the evaporation of the ether, but could 

 generally be spread out into a film again by imparting a sharp twist to the 

 flask. 



Supersaturated solutions of sodic sulphate having films of oil, benzol, 

 turpentine, citronella-oil, &c. upon their surface have been kept by the 

 writer for several months together, and some even as long as eighteen 

 months ; it is true that the oil &c. soon lost the foim of an iridescent 

 film, but could be made to assume it at any moment ; and the above lot of 

 flasks were seldom allowed to stand for a day without being made to do 

 so, i. e. for the first three months after their preparation and at greater 

 intervals afterwards. Every now and then a flask was caused to crystal- 

 lize in order to ascertain that the solutions had in no way lost their sensi- 

 tiveness to a dirty rod ; and when the last flask of all was proved, it had 

 stood for rather more than eighteen months. 



One explanation accounting for the activity of the thin film as prepared 

 by the eminent author of the paper referred to may be this : — That in order 

 to place the oil upon the solution, the flask was opened and exposed to the 

 air, thus affording an opportunity for nuclei to gain entrance ; and also they 

 may have been carried in by the greasy rod itself, for there would be plenty 

 of time in its passage for it to pick nuclei up : such nuclear bodies would 



