1870.] 



On Supersaturated Saline Solutions, 



533 



VII. " On Supersaturated Saline Solutions."— Part II. By 

 Charles Tomlinson, F.R.S. Received May 17, 1870. 



(Abstract.) 



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

 attempted to be established in Part I.*, not only by clearer definitions of 

 terms, but also by new facts and conclusions. The paper is divided into 

 two sections ; in the first of which are stated the conditions 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 tempe- 

 ratures on supersaturated saline solutions. 



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 substance, 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 everything 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 according 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 power- 

 fully ; 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 will 

 do one of three things (apart from chemical action),— (1) it will diffuse 

 through the liquid, and in general, under such circumstances, not act as a 

 * Proc. Roy. Sop. vol. xvi. p. 403 ; Phil. Trana. 1868, p. 659, 



