﻿174 On some Phenomena connected with the Boiling of Liquids. 



delays the boiling of a liquid ; " but these and numerous other 

 phenomena which depend on mechanical molecularity are in a 

 deplorable state of obscurity." He thinks that Gay-Lussac (8) 

 uses the word cohesion in a wider sense than that which opposes 

 the separation of particles. " We must simply conceive that the 

 force which prevents the vapour from forming is an internal 

 force due doubtless to cohesion of the liquid, which the vapour 

 must overcome, and that resistance to change of state which it is 

 more difficult to analyze/" 



28. In 1864 and the following year M. Dufour published 

 two further memoirs* on the phenomena of boiling water, in 

 which he shows that under certain conditions the retardation of 

 the boiling-point takes place at reduced pressures and under 

 atmospheres of hydrogen, street gas, and carbonic acid. As to 

 the action of solids in promoting boiling, he has no doubt that 

 it is due to the air adhering -to them, and they become inactive 

 when this air is removed by the boiling water — and that when 

 the boiling-point of water rises by repeated boiling, the effect is 

 due to the expulsion of air (11). Bits of dry pine-wood, paper, 

 filaments of cotton, &c. lowered the boiling-point. " Soustraits 

 depuis longtemps au contact de Fair, frequemment et longue- 

 ment chauffes dans Feau, ils avaient fini par devenir absolument 

 inactifs : jamais une bulle de vapeur ne se produisait plus sur 

 leur surface, et des retards considerables d'ebullition pouvaient 

 se manifester" (p. 210). 



29. It will be seen from these historical notices that much im- 

 portance is attached to the influence of dissolved air upon the 

 boiling of liquids, as pointed out by De Luc (7) nearly a century 

 ago, and more recently insisted on by Donny (21) and others. 

 It is generally admitted in our text-books (1st) that as soon as this 

 dissolved air has been expelled by heat, liquids boil with difficulty, 

 or produce only sudden flashes of steam; (2nd) that those liquids 

 which have only a weak affinity for air, such as sulphuric acid, 

 alcohol, ether, &c, boil with the greatest difficulty ; (3rd) that the 

 mutual cohesion of the molecules of the liquid, and the adhesion 

 of the liquid to the sides of the vessel, influence the boiling-point, 

 but the adhesion varies with the nature of the vessel and the con- 

 dition of its sides as to roughness or smoothness ; (4th) that the 

 action of solid substances in promoting tranquil boiling and in 

 preventing soubresauts is by carrying down air. 



30. My reasons for dissenting from these conclusions are 

 given in my paper published in the Proceedings of the Royal 

 Society (21, note), to which I beg to refer. 



* Archives des Sciences. Bib, Univ. vol. xxi. p. 201; vol. xxiv. 



