206 On the Formation of Bubbles of Gas and of Vapour in Liquids. 



active so long as their pores are full of air, but when, by long 

 boiling or steeping, the air is expelled they become quite inert*. 



Schonbein was by no means satisfied with the theory which 

 attributed the action of solids in liberating gases or vapours from 

 liquids to their carrying down air, a film of which was supposed 

 to adhere to all bodies exposed to it ; and he expressed his opi- 

 nion that any one would perform an important service both to 

 physics and to chemistry who could satisfactorily account for the 

 varied phenomena connected with the subject of nuclei. 



Although Herr Schroder had not seen the papers either of 

 M. Gernez or myself, yet his own theory is a sort of compromise 

 between the two. M. Gernez says that solids act as nuclei by 

 carrying down air into which the gas in solution expands. I say 

 that such solids act by a kind of differential force depending on 

 the amount of adhesion between gas and an unclean body, and 

 between water and an unclean body. The gas will adhere ; the 

 water, as a rule, will not ; but when it does so, it is with diminished 

 force. Herr Schroder says it is true that unclean bodies act 

 because they are covered, more or less, with a film of fatty or- 

 ganic matter ; but it is this film which enables the air to adhere 

 to the solid, which adhering air, according to him and Gernez, 

 is the efficient cause in liberating gas and vapour from liquids. 



With respect to inactive or chemically clean solids made so 

 by the action of flame, sulphuric acid, &c, I say that the super- 

 saturated solution, whether of gas, of salt, or of steam or vapour, 

 adheres to such solids as a whole (that is, there is the same 

 force of adhesion between the gas, salt, or vapour and the solid, 

 as between the liquid and the solid), and hence there is no sepa- 

 ration. Herr Schroder says that the action of flame, sulphuric 

 acid, &c. is to prevent the air from adhering to the solid, so 

 that when inserted into the liquid there is no separation, because 

 no air has been carried down into which the gas can expand. 



It is not necessary for me to refer to any of the numerous 

 experiments by which I justify my views on this interesting- 

 branch of inquiry. I do not ask Herr Schroder, or any one else, 

 to adopt my theory or my experiments; they must go at their 

 market price in the mart of science ; but I do ask that when 

 an observer takes up a subject which has been already handled, 

 he should make himself acquainted with recent papers which, I 

 suppose, are to be found in every public library ; and when ma- 

 king use of scientific papers, whether old or new, that he acknow- 

 ledge them and quote them fairly. 

 Highgate, N., 



August 11, 1869. 



* Schonbein says, "Gapz bcsomlcrs stark wirkt Holz so langc (lessen 

 Poren noch mit Luft angeflillt sind, abergar niclit mehr, warn (Jjgsc aus- 

 getrieben ist." 



