[ 221 ] 



XXVII. Proceedings of Learned Societies, 



ROYAL SOCIETY. 



[Continued from p. 136.] 



June 16, 1870. — General Sir Edward Sabine, K.C.B., President, in 



the Chair. 

 nnHE following communication was read : — 

 •*• " On Supersaturated Saline Solutions." — Part II. By Charles 

 Tomlinson, F.R.S. 



The object of this paper is to develope more fully the principles 

 attempted to be established in Part I.*, not only by clearer defini- 

 tions of terms, but also by new facts and conclusions. The paper 

 is divided into two sections ; in the first of which are stated the con- 

 ditions under which nuclei act in separating salt or gas or vapour 

 from their supersaturated solutions, while in the second section is 

 shown the action of low temperatures on supersaturated saline solu- 

 tions. 



The first section opens with definitions of the terms used. 



A nucleus is a body that has a stronger attraction for the gas or 

 vapour or salt of a solution than for the liquid that holds it in solution. 



A body is chemically clean the surface of which is entirely free 

 from any substance foreign to its own composition. Oils and other 

 liquids are chemically clean if chemically pure, and contain no sub- 

 stance, mixed or dissolved, that is foreign to their composition. But 

 with respect to the nuclear action of oils &c, the behaviour is different 

 when such bodies exist in the mass, such as a lens or globule, as 

 compared with the same bodies in the form of films. 



Catharization is the act of clearing the surface of bodies from all 

 alien matter ; and the substance is said to be catharized when its 

 surface is so cleared. 



As every thing exposed to the air or to the touch takes more or 

 less a deposit or film of foreign matter, substances are classed as 

 catharized or uncatharized accordingly as they have or have not been 

 so freed from foreign matter. 



Referring to the definition of a nucleus, substances are divided 

 into nuclear or non-nuclear. 



The nuclear are those that may, per se, become nuclei. The non- 

 nuclear are those that have not that quality. 



The nuclear substances would seem to be comparatively few, the 

 larger number of natural substances ranking under the other division. 



Under nuclear substances are those vapours and oily and other 

 liquids that form thin films on the surfaces of liquids and solids ; 

 and generally all substances in the form of films, and only in that 

 form. Thus a stick of tallow, chemically clean, will not act, but a 

 film of it will act powerfully ; and, again, a globule of castor-oil will 

 not act, if chemically clean ; but in the form of a film, whether 

 chemically clean or not, it will act powerfully. 



If a drop of a liquid be placed on the surface of another liquid, it 

 * Phil. Mag. September 1868. 



