and its relation to Latent Heat. 13 



Witli reference to tiu-pentine, Dr. lire and MM. Fabre and 

 Silberman agree nearly as to its latent heat ; but the molecular 

 volume deduced from its capillarity is not in accordance with 

 that deduced from the specific gravity of the liquid and of the 

 vapour ; the latter would require to be twice the observed den- 

 sity. 



With reference to acetic ?ether, it appears that the acetic acid 

 separates from the sether while rising into vapour, as the specific 

 gravity of its vapour is one half what it would be if a volume 

 contained a volume of each of the constituents. If we assume 

 them to be combined to form a single molecule, the absolute 

 volume assigned to it by capillarity is in the proper ratio. And 

 this agrees also if we consider the liquid merely as a mixture 

 with no greater integral of cohesion between a molecule of aether 

 and of acid than between molecules of the sether or of the acid 

 when separate. 



§ 15. The absolute volume of a molecule must augment with 

 the temperature according to the expansion of the liquid. Now 

 the capillary force and the latent heat both diminish as the tem- 

 perature rises. Thus all the elements of the equation [§ 13] 



/ 6 \3 

 m^= ( pry- j are observed to vary with the temperature. Is the 



equation maintained at all temperatures from the point of lique- 

 faction up to the point of transition when the liquid condition 

 suddenly terminates ? 



With reference to the point of transition, first observed by 

 M. Cagniard de la Tour in liquids subjected to high tempera- 

 tures iu sealed tubes, I have made a considerable number of ob- 

 servations in graduated tubes filled with the same liquid in dif- 

 ferent proportions, so as to deduce both the density of the liquid 

 and of the vapour when the liquid state terminates. I found 

 that the cup-shape of the upper surface of the liquid caused by 

 its capillarity, ceased at a temperature considerably uudcr the point 

 of transition. In alcohol the surface (examined closely with a 

 watchmaker's lens) became quite flat at 422^ ¥., and the ])oint 

 of transition occurred at 5 10"^. The density of the vapour at that 

 point being 0'222, and of the liquid 0-480, the density at 85° 

 being unity. In sulphuric scther the surface became flat at 385°, 

 and the point of transition at 437° P., when density of vajjour 

 was 0-230, and of licpiid 0-434. 



]\I. Wolf enclosed a cajjillary tube in a larger tube with icthcr, 

 and, raising its temperature, observed tlie ca|)illary cohunn dis- 

 a])pear at 190° C, and the transition of the liquid at 200° C. 



The disappearance of the capillary colmnn indicates that the 

 liquid has lost tlie power of wetting the glass. Liquid cohesion 

 must nevertheless exist up to the point of transition, and ouglit 



