Mr. C, Tomlinson on Supersaturated Saline Solutions. 387 



and Yiollette, namely that pure oils &c, as used by them, whether 

 in the form of films or globules, do not cause the solutions to crys- 

 tallize, the method indicated opens a new process for ascertaining 

 whether there is really any other nucleus except a salt of the same 

 kind. The statement referred to is as follows : — 



" A solution of two parts of Glauber's salt to one part of water 

 was boiled and filtered into three flasks, which were covered with 

 watch-glasses and left until the next day. A drop of castor-oil was 

 then placed upon the surface of each : it formed a lens which 

 gradually flattened ; but there was no separation of salt, even when 

 the flasks were shaken so as to break up the oil into small globules. 

 .... If, while the flask is being turned round, a sudden jerk be 

 given to it, so as to flatten some of the globules against the side 

 into films, the whole solution instantly becomes solid"*. 



I desire on the present occasion to describe a number of experi- 

 ments in which this process has been observed. But anticipating 

 the objection that the various oils that have been long on my shelves, 

 and already used in former experiments, may really contain various 

 kinds of saline nuclei, I procured from a wholesale house a number 

 of fresh specimens of oil. These were the oils of lavender, bergamot, 

 cajuput, sesame, rape, almonds, olive, and sperm. I did not allow 

 these oils once to enter my laboratory, but kept them in my library, 

 and never opened the phials except in the open air. 



The flasks and dropping-tubes were washed in strong sulphuric 

 acid, and rinsed in tap-water, the tubes being kept immersed in 

 clean water in the open air. The solutions were filtered into the 

 flasks ; and these, being covered with small beakers, were reboiled 

 until steam issued from the orifice. 



The flasks were then taken into my garden, and when cold an oil 

 was dropped upon the surface of each solution. If the oil formed 

 a well-shaped lens, there was no separation of salt ; and in many 

 cases, instead of restoring the small beaker to its place, a well-fitting 

 cork was driven into the neck, and the flasks were thus left for a 

 time, on some occasions extending to the next day. 



In order to avoid the objection that during the shaking crystal- 

 lization might be produced by some of the solution splashing against 

 the cork, many of these experiments were repeated in a pear-shaped 

 flask, nearly 12 inches in height, and containing about 2 or 3 ounces 

 of the solution. Most of the experiments were tried in globular 

 flasks of 5 ounces capacity, with straight cylindrical necks 4 inches 



Experiment 1. Sodic sulphate — 1 salt, 1 water. Solution in tall 

 flask covered with a small beaker. Next day oil of sweet almonds 

 was dropped into it, and the flask corked. After about an hour a 

 circular motion was given to the flask, so as to disperse the oil into 

 minute globules through the solution, giving it the appearance of an 

 emulsion. The flask was left at rest during about an hour, then 

 suddenly shaken, so as to rattle the solution against the side, when 

 all at once, as if with a flash, it became solid. 

 * Phil. Trans. 1871, p. 55. 



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