1881.] On the Viscosity of Gases at High Exhaustions. 455 



any admixture of air. An experiment was accordingly tried with a 

 very volatile hydrocarbon, commercially known as kerosoline, boiling 

 at a little above the ordinary temperature. The vapour of this body 

 was introduced into the well-exhausted apparatus, when the gauge at 

 once sank 82*5 millims. After the usual precautions to eliminate air 

 a series of observations were taken. 



The loss of viscosity is more rapid than with any other gas examined 

 except aqueous vapour. Conversely a very great increase of viscosity 

 occurs on increasing the pressure from 8 to 82'5 millims. The expla- 

 nation of this is that the vapour of kerosoline is very near its liquefy- 

 ing point, and therefore very far from the state of a "perfect " gas. 



The negative bend in the curve at about 10 millims. pressure, 

 already noticed with other gases, is strongly marked with this hydro- 

 carbon vapour. 



Discussion of Results. 



When discussing the viscosity results obtained with the different 

 gases experimented with, the author gives the following approximate 

 comparison of viscosities, such as is afforded by a comparison of the 

 log decrements of each gas and that of air, comparing the ratio with 

 that obtained by Graham, Kundt and Warburg, and Maxwell. 





Graham. 



Kundt and 

 "Warburg. 



Maxwell. 



Crookes. 



1 -oooo 



1 -1099 

 0-971 

 0-971 

 0-807 

 -4855 



1 -oooo 



0-806 

 0-488 



1 -oooo 



0-859 

 0-5156 



1 -oooo 



1-1185 

 "9715 

 0-9715 

 -9208 

 -4439 



1 



Graham's numbers are the theoretical results deduced from his ex- 

 periments on transpiration of gases. They are, he says,* the numbers 

 to which the transpiration times of the gases approximate and in 

 which they have their limit. Graham concludes that the " times of 

 oxygen, nitrogen, carbonic oxide, and air are directly as their densities, 

 or equal weights of these gases pass in equal times. Hydrogen passes 

 in half the time of nitrogen, or twice as rapidly for equal volumes. 

 The result for carbonic acid appears at first anomalous. It is that the 

 transpiration time of this gas is inversely proportional to its density 

 when compared with oxygen." 



The proportion between air and oxygen, nitrogen, or carbonic oxide 

 is not very different at any degree of exhaustion to that which it is at 



# Loc. cit., pp. 178, 179. 



VOL. XXXI. 2 K 



