350 



Physics. — "Tlie virial-coefficieiit B for norival butane." By Prof. 

 J. P. KuEMKN and S. W. Visser. 



(Communicated in the meeting of September 27, 1913). 



Determinations of the vapour density of normal- butane have 

 enabled iis to calculate the virial-coefiicient B in the empirical 

 equation of state as established by Kamerlingh Onnes '). In the 

 course of these calculations anomalies appeared which may be 

 explained by the presence of a small quantity of a lighter admix- 

 ture : a confirmation of this supposition was obtained by determi- 

 nations of the boiling point and from the critical temperature. 



The vapour density was determined by weighing. For this purpose 

 a glass bulb of about .4 litre was used, provided with a stopcock 

 and ground joint by means of which it could be connected to a 

 butane-reservoii', a mercury |)ump, and an 0{)en mercury manometer. 



The volume of the bulb was determined by weighing with air. 

 First the weight of the bulb was determined after having been 

 exhausted as completely as possible by the mercury pump. In all 

 the weighings a tarra-bulb of about the same external volume was 

 suspended from the other arm of the balance: the reading was 

 not taken until the equilibrium had become constant. 



The pressure of the air and afterwards of butane was first of 

 all taken equal to the atmospheric pressure, the temperature being 

 that of the room. For I his purpose a tube some metres long with 

 a stopcock was attached to the filling-apparatus. The gas was 

 admitted to a pressure of about 1 m.m. above the atmospheric: 

 by opening the tap at the end of the long tube for a moment, 

 the excess pressure could be let off without appreciable change of 

 temperature and without fear of outside air penetrating into the 

 bulb. Immediately after closing the bulb the temperature and pres- 

 sure were read. The bulb was then weighed. In tilling the bulb 

 with butane vapour it was three times washed out w4th the vapour 

 and exhausted. 



The barometric pressures were reduced to 0° and in the weights 

 at temperatures above O'' a correction was applied for the ex- 

 pansion of the glass. 



In the same manlier a determination with butane was made at 

 0°, the bulb having been kept in ice for at least half an hour. 

 During the operation the butane reservoir was also placed in ice to 



^) Leiden Gomm. Suppl. 23; § 36; p. 114, sqq. 



