£34 Mr. J. P. Dalton on the Variation of Specific 



(3) With increasing density C v at first increases ; in the 

 neighbourhood of the critical volume it attains a maximum ; 

 and as the density is still further increased it diminishes. 

 This is in accordance with the figures given for isopentane 

 by C. Dieterici * ; but at low temperatures the variation 

 given by him for C v appears to be much too rapid. It is 

 also in accordance with the calculation of C v for isopentane 

 by M. Reinganumt, who finds for C„ a maximum between 

 v = 2'4: c.c. and t*=10 c.c. 



(2) Air. 



In a paper dealing with " the thermodynamic properties 

 of air," A. W. Witkowski J has deduced the variation of 7 

 with the temperature along lines of equal volume, and has 

 given the general features of the (7, 6) diagram ; but with 

 the exception of the results obtained at large volumes and at 

 high temperatures, i. e. in the state of a perfect gas, his 

 conclusions are at variance with those derived from a study 

 of van der Waals's equation and of the behaviour of ether. 

 According to Witkowski, the ratio C^/Cz, first rises with 

 increase of temperature ; atT= — 120° C. (0 = 1*15) it attains 

 a maximum which increases with the pressure ; at higher 

 temperatures it falls again and gradually becomes constant. 

 Since at # = 1'15 there is a maximum value of 7 for every 



volume, ^-q must vanish at that temperature for all volumes. 



Hence, in the isothermal (7, v) -diagram, the isothermal 

 0=1-15 must be crossed by another at all volumes. Of such 

 crossings neither fig. 1 nor fig. 3 gives any indication. 



Witkowski § also gives the (G p , p)- and (C v , p)- diagrams 

 for air. At small pressures the former agrees with the 



results obtained for ether, but when p no longer cc - direct 



comparison is not possible. C v is given as a linear function 

 of the pressure. This is certainly not the case for ether; at 

 large volumes C v is independent of the pressure, but at 

 smaller volumes the curves are concave to the pressure axis. 



E. H. Amagat || calculates 7 for air at T = 50° C. by two 

 methods : — 



(1) from Q P as determined by Lussana, and 



(2) from C v as determined by Joly. 



* 0. Dieterici, Ann. d. Physik, xii. pp. 154-185 (1903). 

 f M. Reinganum, Ann. d. Phi/sik, xviii. p. 1017 (1905). 

 % Witkowski, Phil. Mag. [5]xlii. pp. 1-37 (1896). 

 § Loc. cit. 

 || E. H. Amagat, €. X. cxxii. pp. 60-70 (1896). 



