PROFESSOR GRAHAM ON THE MOTION OF GASES. 
351 
s 
0-8785 referred to oxygen as unity (Regnault), instead of 0-9010 and 0-8750; or 
the observed difference in density is sensibly less than it should be by theory. The 
departure from the law in the transpiration of the same gases is certainly somewhat 
wider, and it is in the opposite direction ; the difference in the observed times of trans- 
piration being greater instead of less than the calculated times. 
The points respecting transpiration which still most demand consideration are the 
following : — 
1. Determination of the resistance and of the dimensions of the capillary at which 
the transpiration of gases becomes normal ; and the properties of serviceable capillary 
tubes. 
2. New determinations of the transpiration of various gases and vapours. 
3. Influence of change of density and elasticity, produced by change of pressure, 
upon transpiration. 
4. Influence of temperature upon transpiration. 
I. CAPILLARY TUBES FOR TRANSPIRATION. 
The transpiration of some gases appears to become sooner normal than others, that 
is, in capillary tubes which are less elongated or less contracted than is necessary for 
other gases. This was first observed on breaking down and using portions of the glass 
capillary tube, H of my former paper, which was comparatively wide, being about 
0-0222 inch, or ^th of an inch in diameter, with the great original length of 22 feet ; 
when it allowed 1 cubic inch of air to pass under the pressure of one atmosphere 
into a vacuum in 15-64 seconds, or it discharged 3-84 cubic inches of air per minute. 
The following table exhibits the times of transpiration of equal volumes of several 
gases by this capillary reduced in length to a little under 20 feet. The table con- 
tains two series of experiments. The first is the transpiration time of a constant 
volume of the gases drawn from a globular vessel standing over water, into a sustained 
vacuum. This vessel was terminated above and below by glass tubes, forming hollow 
axes to the globe. The measure transpired was the capacity of the vessel between a 
mark on the lower and a mark on the upper tube, and amounted to 56-5 cubic inches. 
The second series, which consists of carbonic acid gas, with air for comparison, is the 
transpiration of these gases into a nine-pint jar or receiver upon the plate of an air- 
pump, beginning the experiment with an exhaustion of 28-5 inches by the attached 
barometer, and terminating at 23-5 inches. It was necessary to measure the volume 
of carbonic acid in this manner after transpiration and not before it, to avoid the 
error which the solution of a portion of this gas in water might introduce. The gases 
all passed through a drying tube containing asbestos moistened with oil of vitriol, 
before reaching the capillary. 
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