f 215 ] 



XVII. On the Thermal Behaviour of Liquids. 

 By Prof. William Ramsay and Prof. Sydney Young. 



To the Editors of the Philosophical Magazine. 

 Gentlemen, 



DURING recent years several papers on the thermal pro- 

 perties of gases and liquids, which contain what we 

 believe to be incorrect conclusions, have been published ; and 

 in the interest of accurate knowledge we feel bound to make 

 some comments on them, and to point out in what respects 

 they are erroneous. 



We shall first consider certain observations on the critical 

 point. 



Battelli ( Atti del R. Istituto Veneto di Scienze, iv. serie vii. 

 1892-93 ; also a pamphlet published by Antonelli, Venice) 

 comes to the following conclusions regarding the critical 

 point: — 



" 1. The critical temperature is that at which the cohesion 

 of the liquid particles is so diminished that they no longer 

 remain together, but expand throughout the containing vessel. 



" 2. Above the critical temperature the liquid particles con- 

 tinue to vaporize, i. e. to separate into molecules of saturated 

 vapour, as the temperature rises. 



" 3. Retaining for the term ' critical point ' the significa- 

 tion which it has in the isothermal diagram, the determination 

 of the critical point (temperature ?) by means of the optical 

 method is not generally exact ; because the disappearance of 

 the meniscus takes place at a temperature higher than the 

 critical temperature, and stria3 (intorbimento) appear at a 

 temperature the lower, the greater the amount of liquid 

 contained in the experimental tube." 



Again, in Wiedemann's Annalen, vol. 1. p. 531, Galitzine 

 states that the critical temperature, determined by heating 

 the liquid and allowing it to cool until a meniscus is just 

 visible, is lower than the true critical temperature. He also 

 makes the remarkable assertion that at temperatures con- 

 siderably higher than the critical temperature the substance 

 at constant pressure may have different densities, varying as 

 much as 25 per cent., owing to the formation of liquid com- 

 plexes ! A short account of these conclusions is to be found 

 in 'Nature/ November 23, 1893, and in this Journal, Dec. 

 1893, p. 552. 



Zambiasi and de Heen also state that the temperature at 

 which mist and stride appear when the substance is cooled is 

 lower than the true critical temperature, but in other respects 



Q2 



