44 Mr. C. Tomlinsou on the Motions of certain 



spheric temperature, resting on (I do not say in contact with) a 

 highly supersaturated and consequently very sensitive solution, 

 without any separation of the salt arising from nucleate action. 

 Nay, more, during all this time the flask containing the solution 

 may be shaken so as to disperse the oil in globules through the 

 solution, and yet there is no crystallization. So far as their 

 action as nuclei depends, they might as well be outside the flask. 

 In such a case, as it seems to me, each globule of oil does not 

 adhere to the solution, although this may completely surround 

 it when the flask is shaken, but maintains its own surface-ten- 

 sion, while that portion of the solution which moulds itself upon 

 it and forms, as it were, a new surface, thus acquires and pre- 

 serves its own peculiar surface-tension; so that in fact the oil- 

 globule and the solution are not in contact at all. The extreme 

 sensitiveness of the solution to the action of nuclei renders this 

 view probable. We have only to convert an oil-globule into a 

 film, which may be done by a peculiar jerk of the flask, whereby 

 a few globules flatten against the side and spread, when in an 

 instant, as if by a flash of light, the whole solution becomes 

 solid. By thus converting an oil-globule into a film we ensure 

 contact; and contact is necessary to convert the non-nucleate 

 oil-lens or globule into a nucleate oil-film. Now this condition 

 of film is precisely that w r hich we get when a glass rod, for 

 example, made chemically clean and therefore non-nucleate, is 

 rendered powerfully nucleate by simply drawing it through the 

 hand, whereby it becomes tainted with a film of greasy matter. 

 In like manner a glass rod smeared with oil is a nucleus ; but 

 if the oil be made to roll up into globules, neither the rod nor 

 the oil- globules act as nuclei 18 . 



7 



27. A, mercury (« = 49'1); B, ether; = 096. Ether 



spreads rapidly on the surface of mercury, and then resolves itself 

 into a multitude of small lenses. On repeating the experiment 

 a few times, the surface of the metal became covered with a thin 

 film apparently of greasy matter, arising, as Professor Van der 

 Mensbrugghe suggests, from the ether; but may it not rather 

 have originated in the mercury, which is very difficult to main- 

 tain chemically clean ? Alcohol, benzole, wood-naphtha, and the 

 oils spread rapidly on the surface of mercury, as would naturally 

 be supposed from the great differences between their tension and 

 that of mercury. But a difficulty arises in the case of water, 

 which does not spread on mercury, although its tension is six 

 times less than that of mercury. A drop of distilled water on 



18 The details of this subject, including the action of various liquids 

 besides oils, and the peculiar mode of manipulating with the solutions, are 

 reserved for a separate notice. 



