1821.] Causes of Calorific Capacity, Latent Heat, &;c. 273 



tides, and the greater the force which is requisite to decompose 

 thern, or the greater the adaptation of their parts ; and vice versa, 

 the less these two circumstances, the less will be the temperature 

 of ebullition. With this view our theory and experiment will 

 enable us to determine many interesting things respecting the 

 figure and size of the component particles of different fluids ; but 

 of such speculations I may say something hereafter. 



Though the temperature of ebullition in any fluid must neces- 

 sarily be subject to the influence of external pressure, the same 

 does not hold good with the temperature of the liquefaction of 

 solids. In fluids we may conceive the temperature at which the 

 particles would partially decompose much beneath that at which 

 ordinary ebullition takes place. At all temperatures, therefore, 

 higher than that of corpuscular decomposition, the ebullition is 

 restrained solely by the pressure. We may form an idea how 

 pressure in this case prevents ebullition, by considering, that as 

 decomposition produces a great diminution in the temperature, 

 the elasticity of the aeriform product would be very small ; and, 

 therefore, ifa conversion ofapartof the fluid into vapour could take 

 place, yet from the great diminution of elasticity, theexternalpres- 

 sure would instantly compress it to a density equal to, or greater 

 than, the condensible density to which I have before alluded ; 

 and, therefore, condensation will immediately follow. Hence 

 when the temperature is above that of corpuscular decomposi- 

 tion, and beneath that of ebullition, the efforts of the fluid to 

 convert itself into vapour are instantly counteracted by the 

 external pressure producing too great a contraction in the 

 vaporous product. Beautiful instances of the counteracted 

 efforts to vaporisation may be seen in the subsidings of the 

 unbroken tumefactions of water just before ebullition. Here by 

 some rapid accessions of temperature, the lower parts of the 

 water suddenly vaporise, tumify the surface, and then, being too 

 weak to sustain the superincumbent pressure, recondense before 

 their levity can bring them to the surface. As the temperature 

 rises, the strength of these vaporisations increases, until it be suf- 

 ficient to resist the atmospheric pressure; and then the pheno- 

 menon terminates in ebullition by the boisterous escape of the 

 vapour through the surface. On the contrary, as the tempera- 

 ture diminishes, the energy of the vaporisations decreases, and 

 the surface becomes less ruffled, until it gradually settles into an. 

 apparent calm. During ail this time, however, and even for 

 some time after the tumefactions have apparently subsided, the 

 same phenomena of vaporisations and condensations, there is 

 every reason to believe, continue to take place, though not in a 

 manner so tangible to the senses. In fact, as the same causes 

 «xist, the same phenomena of vaporisation and condensation 

 must invariably ensue at every temperature above that of 

 ebullition in vacuo, which indeed might be made evident in 

 the tumefactions by .only lessening the pressure. To two 

 New Series, vol. n. T 



