184 



The equation of the diameter becomes 



y = — .06453 — .000398 d. 

 or in the more usual form 



7/ = + .04416 — .000398 T. 

 Substituting in this equation our value for the critical temperature 

 6= — 239.91° C. the critical density is found to be 



QYh = .0310. 

 In 1904 Dewar') published an estimate of the density viz. .033, 

 calculated from a couple of liquid densities as determined by 

 himself. ''I 



1) J. Dewar, Proc. R. S. 78 (1904) pg. 251. 



~) If the critical density is derived using the quantities d(j in the small flask as 

 read from fig. 1, the weight of a cc. of hydrogen measured under normal 

 conditions and the volume of the flask as given in note 4 on page 180 the result 

 is Qy'k ~ -033. If the diameter is truly a straight line and thus >j^^ = .031 

 as given in the text, a comparison of o' from the figure and o h'om the diameter 

 would provide a means of correcting fig. 1 for the systematic deviation (see the 

 note mentioned) from the true pressure density diagram. It is found that the 

 direction of the diameter in the neighbourhood of the critical point in the cor- 

 rected figure still coincides within the limits of accuracy with the direction holding 

 for lower temperatures according to the above table. 



