connected with the Boiling of Liquids. 435 



physicists, but, so far as I know, did not have the effect of revi- 

 ving De Luc's theory until I published an account of it in my 

 "Historical Notes/' From 1843 to 1863 it was considered a 

 settled point that, in proportion as water is deprived of air, the 

 character of its ebullition changes, becoming, as it does, more 

 and more abrupt, and boiling, like sulphuric acid, with frequent 

 soubresauts, and the water becomes superheated until relieved by 

 a burst of vapour. In 1863 Mr. Grove stated that if water be 

 boiled in an open vessel it continually reabsorbs air and boils in 

 the ordinary way — although, in a tube with a narrow orifice and 

 with a layer of oil on the water, however long the boiling be con- 

 tinued, a minute bead of nitrogen gas is always to be detected. 

 I have already made some remarks on this form of experiment*. 

 About the same time the experiments of M. Dufour excited con- 

 siderable attention. In order to get rid of the adhesion of the 

 liquid to the sides of the vessel, he heated a mixture of oil of 

 cloves and linseed-oil and dropped into it water heated to 80° or 

 90° C, and then gradually raised the temperature of the bath, 

 in one case until it reached 178° C. (352°'4 F.) ; and he sup- 

 posed the water to be at that high temperature without boiling. 

 Many years ago I showed that drops of water, ether, alcohol, 

 &c. could be deposited on oil heated to 450° or 500° F. when 

 they assumed the spheroidal state and rolled about on the sur- 

 face for a long time: 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. Hence I ventured to suggest in my " His- 

 torical Notes u that the globules in Dufour's experiment were in 

 the spheroidal state, especially as he admits that when they 

 touched the side of the vessel or were touched with solids intro- 

 duced into the bath they exploded. But what strengthens my 

 suspicion is the admission on the part of M. Dufour that glo- 

 bules of water, although still retaining their dissolved air, admit 

 of being superheated in his oil- bath. This is exactly what I 

 found in my experiments on the spheroidal condition of liquids 

 on hot oil ; the globules that sank without exploding contained 

 air, but were protected from the superior heat of the oil by a 

 coating of vapour and by slow vaporization from the surface. 



As to the action of solid nuclei, M. Dufour admits that his 

 results were not always concordant, but were even sometimes 

 contradictory; and he attributes these irregularities to differ- 

 ences in the surface of bodies, to greater or less degrees of rough- 

 ness, to the absence or presence of foreign corpuscles adhering 

 to them, to the presence or absence of an adhering film of air ; 



* Phil. Mag. for March 1872. 

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