361 



Tlie clifFerenoes iii tlie two sets of measnremenls at rooni-lenipe- 

 ratiire also point to accidental changes of the capillary action, 

 possibly dne to the formation or disappearance of a layer of vaponr 

 on the wall of the tnbe. 



The relative viscosity follows from the eqnation 



where the indices 1 and 2 refer to butane and air of J5.°5 respec- 

 tively, while 





l^' = :i^_ioi = .ooo5. 



R .02 



Tiiese equations give for the viscosity of butane vapour relatively 

 to that of air at 15.5° 



at 14.7° ^ = .4661. 



at 16.0° .4666. 



at 100° .6059. 



The viscosity of air at 15.°5 is given by Rankine equal to 0.0001803. 

 The viscosity of normal butane thus becomes 



temp. 14.7 i] .00008404 



16 08413 



100.0 1092 



Of the other saturated hydrocarbons the only ones that we found 

 mentioned are 



methane temp. 0° .0001040 Graham ') 



20° 1201 



isopentane 100° 08851 Rappenecker ^) 



212°. 5 1164 



Sutherland's formula which gives a connection between the tem- 

 perature and the viscosity of the vapour is 



ni = no -T^Tf- 



For isopentane Rappenecker deduces from his observations C =: 500; 

 for normal butane we iind from the above data C = 349. Graha.ai's 

 data for methane give a negative C. 



Isopentane at 100.0° C. corresponds with normal butane at 70.°0 

 (reduced temperature t =: .809). Sutherland's formula gives for the 



1) Graham, Phil. Trans Lontl. Ill, p. 573; 1864. 

 ^) Rappenecker, Zs. Ph. Gh. 72, 695; 1910. 



