﻿Phenomena connected with the Boiling of Liquids. 171 



pletely, points will be found where the water does not adhere, 

 where in fact the adhesion is less than the cohesion of the liquid 

 molecules. The same is true of glass, though cleaned with boil- 

 ing sulphuric or nitric acid. In a platinum vessel cleaned first 

 with fused caustic potash and then with sulphuric acid, the boil- 

 ing-point of water was higher than the temperature of the steam, 

 but not so high as in a glass vessel ; but in this the boiling-point 

 was not so high as in Marcet's experiments (19). The reason 

 probably was that the platinum vessel used was much worn, and 

 contained cracks and scratches (Risse und Schrammen) which 

 probably acted like pulverulent bodies in lowering the boiling- 

 point. 



21. In 1843 Donny published a paper* in which the influence 

 of the air or of gases dissolved in the liquid is made of first-rate 

 importance in studying the phenomena of ebullition. M. Donny's 

 results have been estimated so highly that most subsequent 

 writers have not only adopted them, but have promoted further 

 investigations with reference to them. Whether it be true or 

 not that the dissolved air is so important has been considered in 

 another placef ; but the idea that it is so is by no means new, 

 as already noticed (7), (11), (14), &c. 



22. According to Donn} 7 , boiling is not an inherent property 

 of liquids; they only boil when they contain air — that is, when 

 they are not pure. Heat liberates bubbles of air nearest to the 

 source of heat : each air-bubble presents to the liquid molecules 

 surrounding it a surface which promotes the vaporization of these 

 molecules • and when the tension of the vapour is sufficient to 

 counterbalance the pressure to which these bubbles are submitted, 

 nothing further opposes the development of this vapour, which 

 then forms currents that traverse the liquid and give rise to 

 ebullition. Hence, according to this view, ebullition is a kind 

 of evaporation extremely rapid, which operates upon those inte- 

 rior surfaces of the liquid which limit a bubble of some aeriform 

 fluid J. 



23. If the quantity of air in the liquid be small, the boiling- 

 point may rise ; but the boiling-point is constant only when the 

 liquid contains air. It is difficult, if not impossible, to get rid 

 of the dissolved air; after a burst of vapour a bubble of air may 

 often be seen adhering to the vessel. The boiling-point is also 

 singularly influenced by the forces of cohesion and adhesion — the 



* " Sur la Cohesion des liquides, et sur leur adherence aux Corps 

 solides," Memoires couronnes par VAcademie Roy ale de Bruxelles, 1843 & 

 1844, vol. xvii. published 1845. See also Annales de Chimie et de Physique 

 for 1846, ser. 3. vol. vi. p. 16/. 



\ Proceedings of the Royal Society, January 21, 1869. 



% These views are the same as those put forth by M. De Luc (7). 



