PROFESSOR GRAHAM ON THE MOTION OF GASES. 
593 
The calculated times of the last column are the reciprocals of the tension, or 
number of atmospheres in the first column ; they represent the observed times within 
a sufficient degree of approximation, to prove that for equal volumes of air of different 
densities , the times of transpiration are inversely as the densities. The velocity of 
transpiration will therefore be directly in proportion to the density of the air ; air of 
double density being transpired into a vacuum in half time. 
This at once separates the action of a capillary tube from that of a minute aper- 
ture ; for air of all densities, it will be remembered, passes into a vacuum by effusion 
with equal velocity. 
A consequence of this law immediately appears in conducting transpiration expe- 
riments, in the marked influence of the height of the barometer on the time of tran- 
spiration ; the higher the barometer and the denser the air, the more quickly does 
a constant volume of it pass through a capillary tube into a vacuum. 
This appears also to separate transpiration from the ordinary action of friction, for 
the denser the air, the more should its passage be retarded by friction. 
[2. Transpiration of Air of different Temperatures. 
Dry air was transpired by a glass capillary tube K, of fine bore, 39'4 inches in 
length, into a two-pint jar till the gauge barometer fell from 28*5 to 23*5 inches, in 
796, 794 and 794 seconds, in three successive experiments, made at the temperature 
of 41° Fahr., and with the barometer at 30*052 inches. Four hours afterwards, the 
air and all the apparatus having been for some time at 58°, an equal volume of dry 
air was transpired twice in 814 seconds. A difference of 17 degrees of temperature 
has made a difference of 19 seconds in the time of transpiration, and the dense cold 
air is transpired most rapidly. The times are nearly in the inverse ratio of the 
square root of the densities of air at the two temperatures. 
The transpiration of air in the first experiments which are made in the morning is 
often observed to be more rapid than in those which follow, owing I believe to the 
low nocturnal temperature being retained for some time by the glass capillary. 
January, 1847-] 
3. Preliminary Experiments on the Transpiration of different Gases hy Capillary 
Tubes, A, B and C. 
The times of transpiration of the gases will be expressed in the sequel with refer- 
ence to the time of oxygen as unity instead of that of air. Assuming what is now 
almost universally conceded, that the atomic weights of the following elements are 
exactly expressed by entire numbers, namely, oxygen by 8, nitrogen by 14, carbon by 
6, and hydrogen by 1, and that while the equivalent proportion of the first affords one 
volume of gas, that of each of the others affords two volumes, we obtain the following 
theoretical densities for these elements and several of their gaseous compounds. The 
experimental determinations which appear to be of most value are subjoined. 
mdcccxlvi. 4 H 
