1904] 



Physical Constants at Low Temperatures. 



255 



a temperature as*20°-5 for oxygen we may consider its gaseous density 

 to be practically negligible. Hence one point on Matthias's rectilineal 

 diameter for oxygen will be, at 20°'5, a density equal to 0-7128, the 

 half of that given in No. 4, Table I. In former papers I found the 

 density of liquid oxygen at its boiling point to be 1*138, and of 

 gaseous oxygen at the same point to be 0' 00440 ; half the sum of these 

 is 0*5712, which gives another point on Matthias's diameter at 90*5°. 

 Thus Matthias's diameter for oxygen is 



d = 0-7543-0*002023/ (3), 



and taking the critical temperature as 155° absolute, we get the 

 critical density to be 0*4407, agreeing notably with the usually accepted 

 value. '44. The inference from this is that the density of solid 

 oxygen at the boiling point of hydrogen is 1"4256. 



The results for nitrogen, taken at three temperatures, do not 

 warrant the deduction of a linear relation between d and t, especially 

 as on plotting the observations the concavity of the liquid density 

 curve though slight is quite apparent. However, there are two 

 observations at temperatures so low that the corresponding gaseous 

 densities may be neglected, thus enabling us to construct a Matthias 

 diameter. At the boiling point of hydrogen, the ordinate of the 

 Matthias line is therefore very nearly J (l - 0265) = 0*5133 ; similarly 

 at the melting point of nitrogen the ordinate is J (0-8792) = 0*4396. 

 Hence the Matthias diameter is 



d = 0*5492-0*00175/ (4), 



which for the critical temperature 127° gives the critical density as 

 0*3269. This agrees very well with the value deduced by Matthias* 

 from Wroblewski's liquid densities, namely 0*333, though it is some- 

 what higher than the value 0*299 which he deduced from the theory of 

 corresponding states, f 



Only three observations have been obtained for hydrogen, which 

 again lie nearly on a straight line, but nevertheless present a very 

 slight concavity to the axis of temperature. If we treat the two 

 lowest densities as we have done with nitrogen, we get for the 

 Matthias diameter the line* 



d = 0*04136-0*000247/ (5), 



whence the annexed table (p. 256) of critical densities according to the 

 temperatures chosen for the critical temperatures. Berthelot gives an 

 estimate for the critical density as 0*033, and quotes Wroblewski's 

 critical temperature as 33°, two results closely in accord with the 

 numbers in this table. We are, therefore, justified in considering 



* ' Mem. Soc. Roy. des. Sci. de Liege,' 3rd Series, 1899. 

 f ' Le point critique des corps purs,' p. 176. 



