( 419 ) 



For flie (';ilciihi(i()ii of llic coeflicieiits of llie parulxjla ii sixth 

 j)(>ijif was used which has been iiiserled at (he botloiii of the table, 

 and was obtained bv means of the isotherm of — 1()4°.14. For tliis 

 temperature the value of Ba i^ very sbglit, and by means of inter- 

 polation (he RoYT,E-poin( ean be easily de(erniined. For tliis is found, 

 measured on (lie absolute seale : 



^ = — 165°.72 

 to whieli corresponds a value of pvA = 0.39292. 

 For the coetiticients of the j)arabola we find : 



1\ = - 14.837U 

 I\ z= 4- 676.563 

 P, = — 1624 31 

 The differences of the last column are slight, except for — 195°. 27. 

 For this temi)era(ure ('a a[»|)ears also to be too small (see table XXII). 

 Both deviations must be owing to the not (piite accurate position 

 of one 01' more of the points of the isotherms. From the diagram of 

 Plate I it is already to be seen that (he middle point of series IV 

 probably lies too high. 



The parabola cuts the ordinate p ^ in two points where //i'A is 

 respectively = 0.39330 and 0.02323, with which agree the absolute 

 temperatures : 



Tj = 6.3 T, = 107°.5. 



For the top of the parabola pvA = 0.20826, with which corresponds 

 a pressure of 55.61 atmospheres. From this follows for the absolute 

 temperature of (he isotherm which passes through the top : 



T — 64°.2. 



Physics. — "-Isotlierm.^ of diatomic gases and their binary mixtures. 

 VII. Isotherms of hydrogen between 0^ C. and 100^ C." By 

 Prof. H. Kamerlingh Onnes and C Braak. Communication 

 N". 100^ from the Physical Laboratory at Leiden. 



(Communicated in the meeting of November 30, 1907). 



§ 1. Survey of the determinations. 



The reservoir of 5 cm.' of the piezometer of series IV (Comm. 

 N". 99^' Sept. 1907) was replaced by one of 10 cm.' With this 

 apparatus two isotherms were determined, in ice and in vapour of 

 boiling water. To obtain constant temperatures the same instruments 

 were used as in Comm. N°. 60 (Sept. 1900). The water manometer 

 (c.f. § 8 of Comm. N". 27 (June 1896)) was read, but the difference 



