578 
PROFESSOR GRAHAM ON THE MOTION OF GASES. 
Olefiant Gas . — When this gas is prepared by heating sulphuric acid, of specific 
gravity 1*6, with strong alcohol at the temperature of 320°, in the proportion of six 
parts of the former to one of the latter, it appears to come off at first very pure, as it is 
entirely absorbed by the perchloride of antimony, and contains therefore no carbonic 
oxide. But it is really contaminated, I find, by a portion of another heavier gas or 
vapour (not ether vapour), which cannot be entirely removed from it by washing with 
alkaline water, oil of vitriol, or strong alcohol, and which may raise the density of the 
gas above that of air. As the evolution of gas proceeds, the proportion of the heavy 
compound diminishes, and it finally disappears, and the gas attains its theoretical 
density ; but it is then again contaminated with more or less carbonic oxide. The 
latter gas, however, being of sensibly the same density as olefiant gas, is not likely 
to exert any influence upon its effusion rate. But before these facts were ascertained 
this jet became unserviceable from an accident, and the experiments made with it 
were all made upon the dense olefiant gas, and gave an effusion time which slightly 
exceeded that of air. 
2. Effusion into a Vacuum by a perforated brass plate A. 
A minute circular aperture was made by means of a fine drill in a thin plate of 
sheet brass -g-g-gth of an inch thick, and the opening still further diminished by blows 
from a small hammer, of which the surface was rounded. A small disc of the brass 
plate was then punched out, having the aperture in the centre, which was soldered 
upon the end of a short piece of brass tube, of quill size, so as to close the end of 
the cylinder. This brass tube was then fixed, by means of a perforated cork, within 
the tin tube, used as formerly, for conveying the gas from the gasometer jar to the 
air-pump receiver ; so that the gas should necessarily flow through the small aperture 
in its passage, as before through the glass jet. The aperture was of an irregular 
triangular form, in consequence of the hammering of the plate. One cubic inch of 
air of usual tension passed into a vacuum through this aperture in 12'56 seconds. 
The volume of gas effused in an experiment was the same as before, and the other 
arrangements similar, but the aperture in the brass plate being smaller than that of 
the glass jet, the effusion was considerably slower. 
The constant volume of 22 7 cubic inches of the following gases passed into a 
vacuum of 29’3 inches by the attached mercurial gauge, at the temperature of 63 0, 3, 
in the following times : — 
(1.) Air in 47' 32", or 2852 seconds. 
(2.) Nitrogen in 46' 47", or 2807 seconds. 
(3.) Oxygen in 50' l", or 3001 seconds. 
(4.) Hydrogen in 13' 8", or 788 seconds. 
(5.) Carbonic acid (over brine) in 56' 54", or 3414 seconds. 
