1873.] 



Supersaturated Saline Solutions. 



209 



those of M. Yiollette, and some of them mere variations, such as the proof 

 that bodies greedy of water and capable of being hydrated do not produce 

 crystallization ; onty M. Yiollette made use of calcined sulphate of copper 

 instead of calcic chloride &c* Moreover, no fresh proofs are wanted as 

 to the non-nuclear action of the modified salt or of the anhydrous salt 

 on supersaturated solutions of Glauber's salt. 



Recently, MM. Grernez t and Yiollette J have each, on the occasion of 

 the publication of my third paper (namely, that written in conjunction 

 with M. Yan der Mensbrugghe§), called in question the integrity of my 

 experiments, M. Gernez insisting that the oils and other liquids employed 

 by me contain salts of the same kind as those of the solutions they 

 apparently acted on. 



Such an assertion as this seems to me to be very difficult of proof ; 

 and it seems equally bold to assume that the air of an open garden 

 in the country contains salts of various kinds, watching their oppor- 

 tunity to get into my flasks and vitiate the results of my experiments. 



I desire to invite special attention to a statement made in my second 

 paper ; the more so because, without desiring for a moment to call in 

 question the negative results obtained by MM. Grernez 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 crystallize, 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 be- 

 comes solid" ||. 



I desire on the present occasion to describe a number of experiments 

 in which this process has been observed. But anticipatiug 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, 



* On the surface-tension theory, it is not inaccurate to say that absolute alcohol robs 

 the solution of water, and so determines crystallization, since the mixture of alcohol 

 and water degrades the tension of the solution. 



t Comptes Eendus, vol. lxxv. p. 1705. J Ibid. vol. lxxvi. p. 171. 



§ Proceedings of the Royal Society, vol. xx. p. 342. 



!| Phil. Trans. 1871, p. 55. 



