188 M. F. C. Henrici on the Action of Solid Bodies 



cording to my experiment, be doubted. Once admit the origin 

 of a bubble, an enclosing liquid surface is thus created, into the 

 hollow space of which other bubbles can penetrate, as continually 

 happens at the free outer surface of the liquid, where the air 

 particles can follow the bent of their force of expansion upwards. 



The bubbles have, as a rule, so far as I have been able to 

 make out, a spherical form ; but they assume, in consequence 

 of rapid growth, especially when thick together, an elongated 

 form. In this case I have not remarked that they coalesce 

 (a plain proof of the tenacity of the boundary walls), but they 

 rather, when they have attained a certain size, become detached 

 and ascend. Nor are the bubbles in actual contact with the 

 operating surfaces, which may be accounted for by the adhesion 

 of the liquid to the wet surfaces, whereby the fluid particles 

 lose to a great extent their mobility ; and hence it is intelligible 

 why the bubbles cling with such remarkable tenacity to the 

 surfaces : the smaller ones can scarcely be loosened by striking 

 the vessel, and it is not till they have attained a certain size 

 that they acquire ascensional force sufficient to detach them ; 

 so that on perpendicular or oblique surfaces they often ascend 

 with diminished speed*. The nature of the surface seems from 

 these results to have an influence. The bubbles do not attain 

 so large a size on glass as on metal; the attraction between 

 glass and water must be less than between metal and water, 

 and hence the water particles would have less adhesion to glass. 



If, as I doubt not, the condensation of the air-impregnated 

 water on the immersed surfaces is the cause of the separation of 

 the bubbles, such condensation acting in another way will pro- 

 duce the same result. The following experiments were made 

 with water so slightly impregnated that an immersed silver 

 wire produced no bubbles ; and these experiments illustrate the 

 well-known fact, that aqueous solutions under like conditions do 

 not take up so much gas as pure water. By adding a little 

 sulphuric acid, or portions of concentrated solutions of different 

 readily soluble salts, to the impregnated water, there was a 

 greater or less separation of gas-bubbles on the glass rod or 

 other immersed surface. The following form of experiment 

 gave the most striking results : — A copper wire hanging in a 

 test-glass was twisted at the centre so as to hold some fibres of 

 linen for the reception of the body that was to enter into solu- 

 tion and to retain it at the surface level of the liquid in the 



* Hence doubtless arises the remarkable phenomenon which I have ob- 

 served in using the effervescing powders ; namely, the ascending columns 

 of the smallest bubbles were continually reflected from the under side of 

 the upper surface, while many single ascending bubbles bounded repeatedly 

 therefrom ere they could break through the thin surface. 



