436 Mr. C. Tomlinson on some Phenomena 



and he attributes the sudden change of state in the globules 

 from liquid to vapour to the capillary action of porous bodies. 



The various effects obtained by me from solid nuclei in what 

 I term the chemically unclean or non-catharized state, are ad- 

 mitted by M. Gernez (p. 356); but, while refusing to admit my 

 explanation of them, he invokes the aid of M. Verdet (p. 352), 

 who says: — "The following cause acts doubtless in many cases, 

 perhaps in all. If in certain parts [of the solids] the surface 

 be not wetted by the liquid, and if in these parts there exist very 

 small and very fine asperities, the capillary forces compel the 

 liquid to withdraw from the sides to the neighbourhood of these 

 asperities (as happens when we dip a very fine steel needle into 

 mercury); and in this way is formed a veritable free surface 

 where evaporation is a constant and necessary phenomenon. 

 When the vapour formed between this free surface and the side 

 has acquired a sufficient elastic force, it becomes disengaged and 

 ebullition sets in. In this way it may be explained how sulphur 

 and shellac, which water does not wet, and metals which it wets 

 less completely than glass, are useful in accelerating ebullition. 

 In M. Donny's experiment it was necessary that the tube be 

 first disembarrassed from fatty matter by washing with sulphuric 

 acid; the prolonged boiling of the water had probably for its 

 final object, not only the getting rid of the dissolved air, but 

 also the bringing about a certain chemical action of the water on 

 the glass,, the result of which was to produce a more intimate 

 contact and a stronger adhesion." 



All this is put forth with great ingenuity and ability. At the 

 risk of being tedious, I must here repeat my theoretical views as 

 to the function of solid surfaces introduced into a gaseous solu- 

 tion, or into a liquid at or near the boiling-point. The term 

 "gaseous supersaturated solution" refers to such liquids as 

 soda-water, Seltzer water, champagne, &c; and seeing that, in a 

 large number of cases in which solid nuclei separated gas from 

 them, there was a precisely similar action of nuclei in separating 

 vapour from liquids at or near the boiling-point, it seemed not 

 unreasonable to suppose that these last-named liquids are consti- 

 tuted like the former. (Herr Schroder subsequently adopted 

 the same view*.) Moreover in both cases the received opinion 

 is that nuclei act by carrying down air, into which the gas or the 

 vapour is said to expand, and so escape ; whereas^ according to 

 my theory, I endeavour to show that as gas or vapour will adhere 

 to an oily, fatty, or greasy body, or to a body that has been 

 handled, while water will not so adhere, it is only necessary to 

 introduce such a body into the solution to see that it becomes 



* Poggendorff's Annalen, 1869. 



