5 i8 



SCIENCE PROGRESS 



correcting Baume's calculation, agrees well with that obtained 

 by applying Berthelot's method to Jacquerod and Scheuer's 

 compressibility measurements. 



Excluding the values of A for ammonia and sulphur dioxide 

 given by Jacquerod and Scheuer, the preceding results may be 

 summed up as follows : 



Table VII 



The molecular weights corresponding to the extreme values 

 of Ao given in column 2 are given in column 3, whilst column 4 

 contains the molecular weights calculated from the International 

 Atomic Weights. 



In view of the uncertainty attaching to these values, a 

 detailed discussion is unnecessary. It is, however, obvious 

 that the above values of M cannot afford accurate atomic weight 

 values. Further measurements of compressibilities at o° C. 

 sufficiently comprehensive to reduce the uncertainty attaching 

 to the extrapolation to the smallest possible dimensions are 

 required ; Gray and Burt's method, which determines A' from 

 first principles, as it were, is undoubtedly the best of those 

 hitherto used. 



Reduction of Critical Constants Method 



In this method of determining molecular weights, published 

 by Guye (9) in 1904, the requisite data, in addition to the normal 

 densities of gases, are their critical temperatures and pressures; 

 the determination of A from compressibility measurements, a 

 difficult task as the preceding discussion has shown, is un- 

 necessary. 



The fundamental formula is derived from van der Waals' 

 equation, which Guye applies in a form slightly different from 

 that used by Berthelot. Measuring pressures in atmospheres 



