430 
MR W. CROOKES OK THE VISCOSITY 
These results are plotted on the curve marked “ Kerosoline Vapour,” on diagram A. 
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 explanation of this is that the vapour of 
kerosoline is very near its liquefying point, and therefore very far from the state of a 
“perfect” gas (709). 
The negative bend in the curve at about 10 millims. pressure, already noticed with 
other gases (668), is strongly marked with this hydrocarbon vapour. 
DISCUSSIOH OF RESULTS. 
706. When discussing the viscosity results obtained with the different gases expe¬ 
rimented with, I have given the proportion which I find between the viscosity of 
each gas and that of air, comparing the ratio with that obtained by Graham, Kundt 
and Warburg, and Maxwell, as follows :— 
Air. 
Graham. 
1-0000 
Kundt and Warburg. 
1-0000 
Maxwell. 
1-0000 
Crookes. 
1-0000 
0x Jgen. 
D1099 
1-1185 
Nitrogen. 
0-971 
0-9715 
Carbonic anhydride. . . 
0-807 
0-806 
0-859 
0-9208 
Carbonic oxide .... 
0-971 
0-9715 
Hydrogen. 
0-4855 
0-488 
0'5156 
0-4439 
I have reason to believe that my results are more accurate than those of other 
observers. In the case of hydrogen I have not only obtained a much lower viscosity, 
but the absolute obedience which it pays to Maxwell’s law is an additional proof of 
its purity, for any admixture of foreign gas destroys the uniformity of results (688). 
707. Grahaim’s numbers are the theoretical results deduced from his experiments 
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 con¬ 
cludes that the “times of oxygen, nitrogen, carbonic oxide, and air are directly as 
their densities, or equal iveights 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.” In the Bakerian 
lecture already quoted, when discussing Graham’s results and their bearings upon his 
own experiments on the viscosity of gases, Maxwell says : “It appears to me that 
for comparative estimates of viscosity the method of transpiration is the best.” 
708. It must not be forgotten that the pressure of 760 millims. is not one of the 
constants of Nature, but is a purely arbitrary one, selected for our own convenience 
* Loc. cit., pp. 178-9. 
