( 21)0 ) 



run out were weiglied and afterwards measured by tlie kathetometer. 



Perfect equilibrium of the phases was secured by stirring with 

 an electro-magnetic stiri'ing apparatus, first used and described by 

 KuENEN ^), afterwards applied bv van Eluik ~) and Hartman^). 

 In measuring the volumes, the contents of the stirring-rod had to 

 be taken into account. This volume was calculated from the shape 

 of the stirring rod ; this was very ri'gular, and consisted in an 

 almost perfectly cylindrical part 28,5 m.m. long and on an average 

 of 1,45Ü m.m. in diameter, and two globules, one on each end, of 

 2,300 m.m. and 2,383 m.m. diameter respectively. From these data 

 the volume of the stirring-rod was found to be 60.4 m.m.". 



The compressibility of the mixture was compared with that of 

 pure hydrogen. To this end the experimental tube was connected 

 with another manometer-tube on which, like on the former, a gra- 

 duated scale in m.m. had been etched. The scale was tested by a 

 kathetometer and the manometer was carefully calibrated. This tube 

 however was much iiarrowei- than the first, its section being only 

 about 0,000 cm.". It was filled with a known quantity of pure 

 hydrogen. 



From the specific volumes of the hydrogen, the pressures were 

 calculated by means of the formula 



2J {«;— 0,000690) = 1 + 0,00370 t i) 



borrowed from Amagat's latest observations on the compressibility 

 of hydrogen ■'). 



Volumes and pressures were carefully calculated to within Viooo, 

 as in these experiments no higher degree of accuracy wa» to be 

 expected. 



The two glass manometers were screwed in the usual way into 

 two steel cylinders, which were partly filled with mercury, and for the 

 rest with glycerine which transfered the pressure from a compres- 

 sion-pump. The lower ends of the cylinders were connected by a 

 steel tube filled with mercury ; at their higher ends they communi- 

 cated by means of a brass tube with T-piece for joining on to 

 the compression-pump. 



By connecting the cylinders at their lower ends, a contrivance 



1) he. cit. 



'^) Versl. Kon. Akad., 2'J May 1897; 21 June 1897. Comni., N». 39. 



") Versl. Kon. Akad., 35 June 1S9S. Comm., N". -ta. 



•■) For explanation see a following communication. 



') Annates de Cliim. et de Phys., 6e série, t. XXIX. 



