PROFESSOR GRAHAM ON THE MOTION OF GASES. 
353 
An important conclusion to be drawn from these results is, that the transpiration 
of all gases does not become normal for the same length of tube or amount of resist- 
ance, but that a greater length of the tube and consequent resistance is more neces- 
sary for some than for others. Carbonic acid in particular, of which the effusion 
rate differs so widely from its transpiration rate, appears to require a considerably 
greater resistance than the other gases transpired to bring it to a uniform rate. 
Indeed the results respecting that gas suggest the inquiry whether the resistance is 
sufficient with the present capillary in its greatest length, and whether the true trans- 
piration time for this gas may not be less than 0*75, the number provisionally 
adopted. Let us therefore observe the effect of greatly increased resistances upon 
the transpiration of this and other gases. 
A thermometer tube of the finest flat bore was selected, K, of which 52^ inches 
contained only 13‘5 grains of mercury. The bore was not quite uniform, 0’6 grain 
of mercury occupying 2 inches of the cavity at each end of the tube and 2'3 inches 
near the middle. Under the pressure of 1 atmosphere, 1 cubic inch of air passed 
into a vacuum by this capillary in 15 r3 seconds, or the discharge of air was not more 
than O' 4 cubic inch per minute. The resistance was therefore ten times greater than 
in the capillary H when of its greatest length of 22 feet. 
Air and other gases were transpired through K into a two-pint jar placed upon the 
plate of an air-pump, or into a space amounting to 71 ‘08 cubic inches, till the attached 
barometer of the air-pump fell from 28‘5 to 25‘5 inches. 
(1.) The time required by air in three experiments was 1075, 1073 and 1074 
seconds; and for oxygen in two experiments 1192 and 1192 seconds; the tempera- 
ture being 56°Fahr. and the height of the barometer 30T62 inches. This gives 
0'9010 as the transpiration time of air, referred as usual to the time of oxygen as 1, 
the result accidentally coinciding with the theoretical number for air. 
(2.) The time required by hydrogen in two experiments was 552 and 550 seconds, 
the time of air being 1081, 1079, 1082 and 1080 seconds; thermometer 57° and 
barometer 29*918 inches. Dividing the mean number for hydrogen 551 by the mean 
number for air 1080*5, we obtain 0*5099 as the time of hydrogen, that of air being 1. 
To reduce the time of hydrogen to that of oxygen as 1, we have to multiply 0*5099 
by 0*9010, which gives 0*4593 as the transpiration time of hydrogen. This is a con- 
siderable departure from the theoretical number 0*4375 ; but it was found to be due 
to a small addition of air to the gas, which it obtained from the water over which it 
stood in the pneumatic trough, and necessarily much longer than usual, from the 
slow manner in which it was removed by transpiration through the present capillary. 
In a series of experiments made with hydrogen containing 1,2,4,25, 50 and 75 parts 
of oxygen in 100 of the mixture, this capillary was found to give the transpiration 
times 0*4901, 0*5055, 0*5335, 0*7750, 0*9061 and 0*9718. Half a per cent, of air 
would therefore more than account for the increased time observed with the first 
hydrogen. In experiments, also, made with other equally fine capillaries, when the 
