256 



Prof. J. Dewar. 



[Mar. 9 



tc. 



dc. 



28° 



0-03444 



29 



0*03420 



30 



0-03395 



31 



0-03370 



32 



0-03346 



33 



0-03321 



34 



0-03296 



these hydrogen densities as very closely in agreement with facts, the 

 density at the boiling point coinciding nearly with my former 

 determinations. 



4. Assuming that vapour densities at very low temperatures may be 

 neglected in comparison with corresponding liquid densities, the 

 Matthias diameter enables us to approximate to the molecular volumes 

 of the condensed gases at the absolute zero. For if d' — a — bt be 

 the equation of Matthias's diameter, then d = 2a - 2bt is very 

 approximately the tangent of the liquid density curve near the 

 absolute zero, and therefore l/'2a is the specific volume at absolute 

 zero. 



Hence from the above equations for Matthias's diameter, if V = the 

 molecular volume at absolute zero, we have V = 21*21 for oxygen, 

 Y = 25*49 for nitrogen, and V = 24*18 for hydrogen. The oxygen 

 and nitrogen molecular volumes at absolute zero probably err by 

 defect; but the hydrogen res alt must be taken as very near the true 

 value. 



We may compare these values with the results of theoretical inves- 

 tigation. Guldberg* gives for the molecular volume at zero of 

 oxygen 21*5, and of nitrogen 23*6; and Berthelot'sf values for the 

 same gases respectively are 20*8 and 25*0. From Baly and Donnan'sJ 

 equations for oxygen, nitrogen, carbonic oxide and argon, deduced 

 from observations within the range of temperature 69° — 90° absolute, 

 we find the following values for the molecular volumes at absolute zero : 

 oxygen 20*30; nitrogen 24-04; carbonic oxide 24-54; argon 20'34. 



Again, the Waterston-Avenarius formula connecting temperature 

 and fluid volume, namely, 



v = c-d\og(A-t) (6), 



where A is the critical temperature, gives the following equations, 

 from Baly and Donnan's results, 



* c Zeit. f. Plrys. Cliein.,' 1895, vol. 16, p. 7. 



t ' Comptes Kendus,' March, 1900. 



X ' Jo urn. Chem. Soc.,' July, 1902, pp. 911—914. 



