PROFESSOR GRAHAM ON THE MOTION OF GASES. 
383 
time of aqueous vapour does not differ greatly from that of air itself. The influence 
of aqueous vapour upon the time of hydrogen, however, is considerably less than that 
of air upon the same gas, and therefore suggests a more rapid transpiration. 
17* Alcohol. 
Air was impregnated with the vapour of alcohol of specific gravity 0'835 at 60°, 
barometer 29'358. The tension of the vapour of alcohol of specific gravity 0‘813 at 
60° is estimated at T23 inch. The capillary K, 8'76 inches in length, was made use 
of, with an air-pump vacuum, as in all these experiments. 
The time of dry air was 1013 and 1014 seconds ; of air containing alcohol vapour, 
1011 and 1012 seconds. The rate of air is scarcely affected, and consequently the 
time of alcohol vapour must approximate to that of air. 
1 8. Naphtha and Coal-gas. 
In experiments made with air saturated with the vapour of coal-tar naphtha at 62°, 
the capillary K being employed, the times obtained for air alone were 978 and 979 
seconds ; for air saturated with naphtha vapour, 949 and 949 seconds. The trans- 
piration time of air is diminished 30 seconds, showing that the volatile hydrocar- 
bons of naphtha are highly transpirable, like ether vapour. The time of coal-gas, 
taken from the service-pipes of a London company, and observed in the same cir- 
cumstances, was 621 and 622 seconds; of the same coal-gas impregnated with 
naphtha vapour, 621 and 621 seconds, or the naphtha vapour produced no sensible 
change in the transpirability of the gas ; showing a near coincidence in their trans- 
pirabilities. The transpiration time of the coal-gas, reduced to the oxygen scale, is 
0’5716, or a little more than protocarburetted hydrogen, 0‘5510. 
That a considerable quantity of naphtha vapour was taken up by the coal-gas, 
notwithstanding that its transpiration was unaffected, appears in certain experiments 
which were made with a particular object upon the effusion of the same gases. The 
capillary was removed and replaced by a plate of platinum foil, G of former paper, 
having an extremely minute aperture, the other arrangements remaining the same. 
The gases were all moistened with water. For the passage of equal volumes into an 
air-pump vacuum (the six-pint aspirator-jar, through the usual range from 28’5 to 23'5 
inches of the attached barometer), the times were, at 61°, for air, 434 and 434 seconds ; 
for hydrogen, 139 and 139 seconds; for coal-gas, 314 and 314 seconds; for coal-gas 
saturated with naphtha vapour at 61°, 331 and 331 seconds; for hydrogen and naphtha 
vapour, 194 and 193 seconds ; and for air with naphtha vapour, 503 and 503 seconds. 
It is to be remembered that the densities of the gases effused are in the proportion of 
the squares of these times, and may be deduced from the latter. The time of coal- 
gas is increased by the addition of naphtha vapour, but to a much less extent, than 
hydrogen and air are, no doubt from the former being from the first partially saturated 
with naphtha vapour. 
3 D 2 
