304 Mr. C. Tomlinson on the Action of Solids 



between the sides and the gaseous solution is perfect; and 

 therefore the sides may be regarded, pro rata, as merely a con- 

 tinuation of the liquid itself, and no bubbles will form there 

 any more than in the central parts of the liquid. (2) But sup- 

 pose the sides to be chemically unclean, adhesion is diminished 

 or destroyed, and therefore the surface of the liquid next to 

 such sides is virtually as free as its upper surface ; consequently 

 bubbles will form there, just as they do on the upper surface ; 

 only in the latter case they do not appear as bubbles (except 

 during 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, since it is no function of air to induce the libera- 

 tion of gas or the formation of gas-bubbles. It is really want 

 of adhesion. A glass rod or other solid introduced into 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, because the ad- 

 hesion between it and the gaseous solution is perfect. If dirty, 

 the adhesion is imperfect, and the surface of the liquid in con- 

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



I must refer to my paper for the experimental details ; but I 

 may be permitted to state briefly, that the various solids made 

 chemically clean, or partly so, and plunged into soda-water, dis- 

 played no gas-bubbles except on the parts that had not been 

 made clean — that a flint-stone was immediately covered with 

 bubbles, but, broken into two parts, not a single bubble ap- 

 peared on the newly fractured surfaces — that a rat's-tail file, 

 properly cleaned, liberated no bubbles ; so that I could not 

 agree with M. Gernez that a solid, whatever its polish, "is 

 covered with roughnesses that form a sort of network of capil- 

 lary conduits, into which the surrounding gases penetrate and 

 condense/ 5 that " the gas-bubbles thus imprisoned become the 

 centres to which those that are dissolved pass." 



But M. Gernez says that if a small cavity be worked into the 

 end of a glass rod, and this, full of air, be lowered into a 

 gaseous solution, the gas escapes into it in bubbles. I sub- 

 merged a cage of fine wire gauze in soda-water, but there was 

 no escape of gas so long as it was chemically clean. When 

 taken out, rolled between the slightly greased hands, and again 

 lowered into the soda-water, the gas escaped from its side in 

 bubbles with an audible noise. 



Now it cannot be maintained that contact between the cage 

 and the hands imparted to the cage a film of air instead of a 

 film of oil — or that a slightly greasy rod introduced into a che- 

 mically clean glass containing soda- water, and rubbed against 



