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THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
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<S iowmarket, Sutton, Charles W. 
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Stratton St. Mary, Cooper, Frederick T. 
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Strood, Picnot, Charles . 
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Sutton Coldfield, Smith, William . 
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Taunton, Grose, Nicholas M. 
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Tipton , Briggs, James. 
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Torquay , Bridgman, William L. 
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Uttoxeler, Johnson, J. B. 
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„ Taylor, John . 
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Ware, Medcalf, Benjamin . 
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Yeadon, Blatchley, Thomas. 
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frafetial Sratmctioiw. 
BRISTOL PHARMACEUTICAL ASSOCIATION. 
The Seventh General Meeting of the session was held at 
the Museum and Library, Bristol, on Friday, April 4th. 
The President, Mr. Townsend, occupied the chair, and 
briefly introduced Mr. Carteighe, of London, who delivered 
a lecture, of which the following is an abstract:— 
On the Diffusion and Occlusion of Gases. 
BY MICHAEL CARTEIGHE, F.C.S. 
Dalton’s experiments’on the diffusion of gases, published 
in 1801 and 1803, were explained and referred to by way 
of introduction to Graham’s more exhaustive researches 
on the subject. 
The experiments of the latter physicist and chemist on 
free diffusion, diffusion through porous septa, e. g. plaster, 
graphite, etc., were shown, and the methods demonstrated 
by which the velocity of diffusion and diffusion volumes 
of the more important gases were determined. 
The now well-known law, viz. that the volume of a gas 
diffused in a given time is in an inverse ratio to the square 
root of its specific gravity, i. e. the lighter the gas the 
greater its diffusibility, was explained, and the experi¬ 
mental data upon which it is founded exhibited by dia¬ 
grams. The lecturer then defined atmolysis or air ana¬ 
lysis, and showed the experiment by means of which the 
volume of oxygen in atmospheric air can be increased 
from 21 to 25 per cent, by the passage of a slow current of 
air through a series of tobacco pipe stems, owing to the 
superior diffusibility of the nitrogen. Similarly the more 
diffusible hydrogen of electrolytic gas can be in great part 
separated from the less diffusible oxygen. 
The nature of diffusion and its bearing upon the con¬ 
stitution of matter were explained in the following terms :— 
The pores of artificial graphite appear to be so minute, 
that a gas in mass cannot penetrate the plate at all. 
Molecules only can pass ; and they may be supposed to 
pass wholly unimpeded by friction, for the smallest pores 
that can be imagined to exist in the graphite must be 
tunnels in magnitude to the ultimate atoms of a gaseous 
body. The sole motive agency appears to be that intes¬ 
tine movement of molecules which is now generally recog¬ 
nized as an essential property of the gaseous condition of 
matter. 
According to the physical hypothesis now generally 
received, a gas is represented as consisting of solid and 
perfectly elastic spherical particles or atoms, which move in 
all directions and are animated with different degrees of 
velocity in different gases. Confined in a vessel, the 
moving particles are constantly impinging against its 
sides and occasionally against each other, and this contact 
takes place without any loss of motion, owing to the per¬ 
fect elasticity of the particles. If the containing vessel 
be porous, like a diffusiometer, then gas is projected 
through the open channels by the atomic motion already 
described and escapes. Simultaneously the external air 
is carried inwards in the same manner, and takes the 
place of the gas which leaves the vessel. To this atomic 
or molecular movement is due the elastic force with the 
power to resist compression possessed by gases. The 
molecular movement is accelerated by heat and retarded 
by cold, the tension of the gas being increased in the first 
instance and diminished in the second. Even when the 
same gas is present both within and without the vessel, 
or in contact with both sides of our porous plate, the 
movement is sustained without abatement,—molecules 
continuing to enter and leave the vessel in equal number, 
although nothing of the kind is indicated by change of 
volume or otherwise. If the gas in communication be 
different, but possess sensibly the same specific gravity 
and molecular velocity, as nitrogen and carbonic oxide do, 
an interchange of molecules also takes place without any 
change in volume. With gases opposed of unequal density 
and molecular velocity, the permeation ceases to be equal 
in both directions. 
The movement of gases through the graphite plate 
appears to be solely due to their own proper molecular 
motion, quite unaided by transpiration. It seems to be 
the simplest possible exhibition of the molecular or diffu¬ 
sive movement. This pure result is to be ascribed to the 
wonderfully fine porosity of the graphite. The intersti¬ 
tial spaces appear to be sufficiently small to extinguish 
capillary transpiration entirely. The graphite plate is a 
pneumatic sieve, which stops all gaseous matter in mass, and 
permits molecules only to pass. 
The permeation through the graphite plate into a 
vacuum, and the diffusion into a gaseous atmosphere, 
through the same plate, are due to the same inherent 
mobility of the gaseous molecule. They are the exhibi¬ 
tion of this movement in different circumstances. In in¬ 
terdiffusion we have two gases moving simultaneously 
through the passages in opposite directions, each gas 
under the influence of its own inherent force; while with 
gas on one side of the plate, and a vacuum on the other 
side, we have a single gas moving in one direction only. 
The latter case may be assimilated to the former if the 
vacuum be supposed to represent an infinitely light gas. 
We may speak of both movements as gaseous diffusion ; 
the diffusion of gas into gas (double diffusion) in the one 
case, and the diffusion of gas into a vacuum (single diffu¬ 
sion) in the other. The inherent molecular mobility may 
also be justly spoken of as the diffusibility or diffusive 
force. 
The diffusive mobility of the gaseous molecule is a 
property of matter fundamental in its nature, and the 
source of many others. The rate of diffusibility of any 
gas has been shown to be regulated by its specific gravity, 
the velocity of diffusion varying inversely as the square 
root of the density of the gas. This is true, but not in 
the sense of the diffusibility being determined or caused 
by specific gravity. The physical basis is the molecular 
mobility. The degree of motion which the molecule pos¬ 
sesses regulates the volume which the gas assumes, and 
is obviously one, if not the only, determining cause of the 
peculiar specific gravity which the gas enjoys. If it were 
possible to increase in a permanent manner the molecular 
motion of a gas, its specific gravity would be altered, and 
it would become a lighter gas. 
It is conceivable that the various kinds of matter, now 
recognized as different elementary substances, may possess 
one and the same ultimate or atomic molecule existing in 
different conditions of movement. The essential unity of 
matter is an hypothesis in harmony with the equal action 
of gravity upon all bodies. We know the anxiety with 
which the point was investigated by Newton, and the care 
he took to ascertain that every kind of substance—metals, 
stones, woods, grain, salts, animal substances, etc., are 
similarly accelerated in falling, and are therefore equally 
heavy. 
In the condition of gas, matter is deprived of numerous 
and varying properties with which it appears invested 
