— 155 — 



mic, von Rechenberg 1 ) considered himself called upon to make a rejoinder, 

 of which the substance may be summarised as follows: — 



von Rechenberg had pointed out that the vapour- temperatures publi- 

 shed by F. Krafft and his assistants and obtained by them with the air- 

 pump in their boiling-experiments with the vacuum of the cathode-rays, 

 which they described as boiling-points, were not really boiling-points 

 because there was no indication of the vapour-pressure. Hansen has now 

 admitted this. 



von Rechenberg has also shown that these vapour-temperatures cannot 

 be used as physical constants, i. e. as fixed points, because they are de- 

 termined only by the variable conditions of experimental methods, and 

 because these conditions cannot be adhered to so accurately that they are 

 capable of being observed in a precisely similar manner by every other 

 investigator. 



Finally, von Rechenberg has shown that the evaporation tests publis- 

 hed by Hansen, and adduced by him as proofs against von Rechenberg's 

 statements, do not apply to those statements. 



In our Report of April 1908, (p. 163 of the German and p. 159 of the 

 English edition), while discussing a paper by Hardy and Richens, we rep- 

 resented the authors as having stated that "the use of a fractionating head 

 on the distilling flask has no important influence on the result". Mr. Hardy 

 writes that this statement is based on a misunderstanding on our part and 

 that the meaning of the passage in question was that the authors had 

 found the effect of the distilling head to be less in steam distillation than 

 in dry distillation. We take this opportunity of correcting the statement 

 in our Report referred to above. 



The four lines H«, H/?, H/ and D hitherto in use for determining atomic 

 refractions, as established by Landolt, Bruhl and Conradi, have never been 

 observed in the same material. Moreover, they had been calculated at 

 the globular molecular weights (H = 1) which, in the case of compounds 

 rich in hydrogen, may account for a difference of up to 0,1. For these 

 and other reasons, F. Eisenlohr 2 ) has undertaken a new calculation of the 

 atomic refractions. The values established by him for the D-line are 

 reproduced in the table below: — 



Table of atomic refractions for the D-line: 



Group CH 2 CH 2 4,618 



Carbon C 2,418 



Hydrogen H 1,100 



Oxygen in carboxylic bond . O" 2,211 



x ) Zeitschr. f. physik. Chem. 75 (1910), 628. 

 2 ) Zeitschr. f. physik. Chem. 75 (1910), 585. 



