822 



h'k for [fk indicated there, only some tj^pes lead to simple results^), 

 among others also (with some restriction, see later on) the exponen- 

 tial type proposed already before by Kamerlingii Onnes : 



— « {v — X\) 



h = b,, — {h,,—b^\p 



Already in 1901 (Archives Teyler (2) T. VII, Troisième partie) I 

 tested (see p. 14 et seq.) the values of h for H^ and CO^ by this 

 equation ^), and found a good agreement. But that I then found 

 de\'iations with respect to the critical quantities is simply owing to 

 this that I at the time did not take h,, variable with the tempera- 

 ture, and that therefore observations of H^ at 0° C. can by no means 

 give a final decision about the quantities at — 241° C. 



It is of course only of formal importance, when in the above 

 relation and others at last b,, and ?;„ are replaced hy critical quanti- 

 ties, so that the relations (21) are satisfied. But this will be discussed 

 in a subsequent paper. 



Fontanivent sur Clarens, January 1914. 



Physics. — "An apparatus for the determination of gas isotherms 

 up to about 3000 Atm." {Continuation.) Van der WAALS-fund 

 researches N". 6. By Prof. Ph. Kohnstamm and K. W. Walstka. 

 (Communicated by Prof. J. D. van der Waaes.) 

 (Communicated in the meeting of January 31, 1914). 



B, The volume measurement. {Continuation). 

 Conveyance of the gas into the measuring tube. 



In the previous communication the question was answered how 

 the volume is determined of a quantity of gas which is in the 

 measuring tube, above mercury. Now we shall have to describe how 

 we get the gas quantit} that is to be measured, in this position. 

 For this the most intricate part of the apparatus is required. 



As is known Amagat's measuring tubes consisted of piezometers 



1) Also V. D. Waals' relation in the general form ~ = / 



V — h 



^ . b-h. 



^—^0/ _i 



with bo constant gives perfectly impossible results, among others n varying between 

 8 and 3Ü. 



2) It is easy to see that the relation used there, viz. 



r 



b=b^ {l — (9e~'^'(^) 

 by the application of suitable substitutions for 6 and (3 is identical wiih the above 

 relation. 



