355 



which means a further rise of the boiUng point: the final value 

 may be taken at — 0.6° C. 



A further confirmation of the presence of an admixture like ethane 

 is afforded by the value of the critical temperature (150.8°). When 

 for the various saturated hydrocarbons a graphical curve is drawn 

 with the molar weights as abscissae and the corresponding critical 

 temperatures as ordinates, the value found for butane seems to be 

 a little too small. By representing the critical temperatures of ethane 

 (305°.3), pentane (470°.3), hexane (507°.9), heptane (539°.95) and 

 octane (569°.3) as an arithmetical series of the foui-th order, we 

 find for propane 370°. 25 instead of the experimental value 370°. 1 

 and for butane 424°. 94, i.e. l.°04 higher than what was obtained 

 b}^ us. This result also points to a deviation of the critical tempe- 

 rature owing to the presence of a more volatile admixture. 



Physics. — ''Tlie viscosity of the vapour of norinal butane". By 

 J. P. KuENEN and S. W. Visser. 



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



For the determination of the viscosity of butane vapour Rankine 's ^) 

 transpiration method was used ; a method which is very simple and 

 requires very little vapour, and in which the vapour comes into 

 contact with glass and mercury only. 



The apparatus consists of a long 6^-tube placed vertically and 

 capable of being turned over on a horizontal axis. One arm of the 

 is capillary, the other one a wider tube. The vapour is forced 

 through the capillary by a falling drop of mercury in the wide tube. 

 When the drop has arrived at the bottom of the tube, the apparatus 

 is simply turned upside down, and the drop now drives the gas 

 through the capillary^ in the opposite direction. The time is measured 

 between the moments at which the mercury passes two marks on 

 the fall-tube. The whole tube is mounted in a glass jacket, where 

 the temperature is kept constant. 



In order to be able to w ork with a long capillary \yithout making 

 the apparatus unwieldy by its length, a capillary is used which is 

 twice bent round : hereby it becomes alnu)st three times as long as 

 the wide tube. 



1) A. 0. Rankine, Proc. Roy. Soc. London A 83, 265, olG; 1910. 



23* 



