﻿Phenomena connected with the Boiling of Liquids. 173 



a mixture of oil of cloves and linseed-oil, and this was gradually 

 raised to 110° or 115° ; and the water did not burst into vapour 

 unless it touched the sides of the vessel or the thermometer. 

 The smallest globules of water bore the higher temperatures 

 best : those of 10 millims. diameter were raised to 120° or 

 130° C. ; while those of from 1 to 3 millims. were raised to 178°, 

 when the vapour has an elastic force of 8 or 9 atmospheres'*. 



26. Solids brought into contact with the globules liberated 

 vapour with a hissing noise. Porous bodies, such as wood, 

 chalk, cotton, paper, &c, produced this effect best. A glass rod 

 or a metallic wire did not always act in this way. A platinum 

 wire by frequent use appeared to lose the power of causing sud- 

 den vaporizationf. Porous bodies act best because they carry 

 down air in which the globule begins to evaporate and expand. 



27. M. Dufour rejects the theory which attributes the retar- 

 dation in boiling to the adhesion of the liquid to the sides of the 

 vessel. The contact of solids may prevent the liquid from rising 

 above its boiling-point. The real explanation is to be found in 

 the molecular relations of liquids — in a sort of internal cohesion. 

 When a liquid is near the boiling-point, these molecular influ- 

 ences act as excitants to change of state. The adhesion to the 

 sides of a vessel also excites a peculiar molecular condition in 

 the liquid, and it is at the sides that this molecular equilibrium 

 is disturbed and boiling takes place. But when the aqueous 

 globule is immersed in a fluid with which water does not mix 

 and is raised to a high temperature, it is the contact of a solid 

 that disturbs the mechanical structure of the globule and induces 

 change of state. Heat alone, acting on water protected from the 

 air, contact of solids, and other disturbers of the molecular con- 

 dition, cannot produce change of state, except very much above 

 the temperature usually recognized as the boiling-point. But 

 M. Dufour admits that the molecular influences or disturbers 

 unfortunately present so many irregularities, that they have hi- 

 therto escaped the controlling action of any regular law. He 

 thinks there must be some other force besides cohesion that 



* I have no doubt that the globules were in the spheroidal state, as in 

 De Luc's experiment (7, note *, p 165). More than thirty years ago I pub- 

 lished in my ' Student's Manual of Natural Philosophy,' p. 553, an'aecount of 

 some experiments in which water, alcohol, ether, and^ some other liquids 

 were gently delivered from a dropping-tube to the surface of a fixed oil 

 heated to 450° or 500° F. The liquid drops rolled about on the surface in 

 the spheroidal state ; and in some cases, when a drop slipped beneath the 

 surface, it exploded and scattered the oil about ; but in other cases it was 

 shot up again to the surface, where it continued to roll about as before. 



t Dufour says in another part of his memoir that glass is less active as a 

 promoter of vaporization than metal. " 11 semble que le frequent usage 

 d'une pointe de platine contribue a l'amener a cette sorte de passivite." 



