230 Mr. C Tomlinson on the "Inactive" Condition of Solids, 



A supersaturated solution of a gas with its upper surface freely 

 exposed to the atmosphere is always giving off gas, either with 

 effervescence or silently and imperceptibly. It does so because 

 the excess of gas has but a slight adhesion to the liquid, and 

 the air is virtually a vacuum for it — the only difference being 

 that it would pass off into a real vacuum instantaneously. Novy 

 the remaining surface of the liquid, or that confined by the sides 

 of the vessel, may be regarded as being in exactly the same con- 

 dition, subject, however, to two modifications — (1) the state of 

 chemical purity of their surface, and (2) the pressure exerted by 

 them virtually on the liquid. (1) Suppose the vessel to be che- 

 mically clean. No gas will be disengaged and no bubbles will 

 form on the sides, because the adhesion between the sides and 

 the liquid is perfect; and therefore the sides may be regarded, 

 pro rata, as merely a continuation of the liquid itself, and no 

 bubbles will form there any more than in the central parts of 

 the liquid. (2) But suppose the sides to be not chemically clean 

 . — to be dirty, in fact ; adhesion is diminished or destroyed ; and 

 therefore the surface of the liquid next to such sides is virtually 

 as free as its upper surface; bubbles consequently will form 

 here, just as they do on the upper surface : but in the latter case 

 they do not appear as bubbles (except in effervescence) because 

 there is no pressure ; the sides do exert pressure, and therefore 

 bubbles are formed. Now it does not matter whether there be 

 air or not between the sides and the liquid : there may be any 

 kind of gas, possibly a vacuum, and the result will be the same. 

 It is no function of air to induce the liberation of gas or the for- 

 mation of gas-bubbles. It is really want of adhesion. Now 

 apply this to the case of a so-called u inactive" glass rod, a coin, 

 a fragment of flint, &c. A glass rod placed in the liquid does 

 nothing more than form new sides, as it were, to the vessel, and 

 its effect is merely that of the sides. If chemically clean, the 

 rod will form no bubbles around it, and hence it is " inactive," 

 because its adhesion is perfect. If dirty, the surface of liquid in 

 contact with it will be as free, or almost so, as the upper surface. 

 The same theory holds good, as I shall hereafter endeavour to 

 prove, in the case of nuclei, in inducing crystallization in saline 

 solutions. By means of this same theory I shall also attempt to 

 reconcile the numerous and often conflicting statements respect- 

 ing ebullition, and the effect of chemical purity or otherwise on 

 the boiling-points of liquids, — all of which, 1 imagine, depend on 

 the same law of adhesion, and have nothing to do with the air, 

 except indirectly. 



King's College, London, 

 August 20, 1867. 



