MR. CHARLES TOMLINSON ON SUPERSATURATED SALINE SOLUTIONS. 
53 
A second class of nuclear bodies are permanently porous substances, such as charcoal, 
coke, pumice, meerschaum, See. The action of these is chiefly confined to vaporous solu- 
tions, and, if catharized, they have no power of separating salts from their supersaturated 
solutions. 
Under the non-nuclear, forming by far the larger class of substances, are glass, the 
metals, &c., while their surfaces are chemically clean ; and by chemically clean is meant, 
as already noted, wholly free from any substance foreign to their own composition. 
Among the non-nuclear will be found air ; for its ascribed nuclear character is due, 
not to itself, but to the nuclear particles of which it is the vehicle. Thus, as stated in 
former papers, if air be filtered through cotton-wool, it loses its apparent nuclear action ; 
so also if heated. 
I have already published numerous examples from the recorded experiments of 
Oeksted, Schonbein, Liebig, Lowel, and others ; and I have also shown by new experi- 
ments 5 that Class II., namely the non-nuclear, are really so, and have only been thought 
otherwise for want of adverting to the condition to which I first called attention, 
namely their being in a catharized state or not. To run through all the substances 
of which this may be predicated were impossible. To treat of a few will answer the 
purpose if we show that those which have been thought to have the quality of nucleus 
do not possess it, but only seem to do so, by having their surfaces soiled with foreign 
matter or films that really do possess the power. The only answer that such a view 
admits of as to those substances is manifestly to show that they had been catharized 
previously to experiment, and yet were found to be active as nuclei. 
My former papers contain sufficient details as to the general action of nuclei in sepa- 
rating gases, vapours, and salts from their supersaturated solutions. When the nucleus 
is catharized or clean, it has no such separating action, because the solution adheres to 
it as a whole, that is, there is the same adhesion between the gas or vapour or salt and 
the nucleus as between the liquid part of the solution and the nucleus ; but when the 
nucleus is non-catharized or unclean, the gas or vapour or salt adheres to the surface 
more strongly than the liquid part of the solution, and hence there is a separation of 
gas or vapour or salt from solution. My present purpose is to show that an active 
nucleus, or unclean or uncatharized surface, is contaminated with a film of foreign 
matter, which filmy condition is necessary to that close adhesion which brings about 
the nuclear action ; for it can be shown that a liquid, such as an oil, is non-nuclear in its 
action when in the form of a lens or globule, but powerfully nuclear when in the form 
of a film. 
There are certain liquids which form films, and act as nuclei by separating water 
instead of salt from supersaturated solutions. Absolute alcohol acts in this way. 
Other liquids, such as glycerine, diffuse through the solution without acting as nuclei. 
Saline solutions may also saponify fatty oils, or otherwise act chemically upon them, 
5 Journal of the Chemical Society for April 1869. Chemical News, 1868, 1869, 1870. See also notes 
O, 0, 0. 
