May 3, 1873.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
871 
whet in the form of a liquid or solid. The gas exhibits 
only a few grand and simple features. These, again, may 
all be iependent upon atomic or molecular mobility. 
If \*e imagine one kind of substance only to exist 
ponderable matter—and further, that matter is divisible 
into ultimate atoms uniform in size and weight, we then 
shall ha\e one substance and a common atom. With the 
atom at rest, the uniformity of matter would be perfect, 
but the atom possesses more or less motion, due, it must 
be assumed, to a primordial impulse. This motion gives 
rise to volume. The more rapid the movement the greater 
the space occupied by the atom, somewhat as the orbit of 
the planet widens with the degree of projectile velocity. 
Matter is thus made to differ only in being lighter or 
denser matter. The specific motion of an atom being in¬ 
alienable, light matter is no longer convertible into heavy 
matter. In short, matter of different density forms different 
substances—different inconvertible elements, as they have 
been considered. 
Moreover, these more or less mobile, or light and 
heavy forms of matter, have a singular relation connected 
with equality of volume. Equal volumes of two of them 
can coalesce together, unite their movement, and form a 
new atomic group, retaining the whole, the half, or some 
simple proportion of the original movement and conse¬ 
quent volume. This is chemical combination. It is di¬ 
rectly an affair of volume, and only indirectly connected 
with weight. Combining weights are different, because 
the densities, atomic and molecular, are different. The 
volume of combination is uniform, but the fluids measured 
vary in density. This fixed combining measure weighs 
1 for hydrogen, 16 for oxygen, and so on with the other 
elements. 
This hypothesis admits of another expression. As in 
light we have the alternative theories of emission and 
undulation, so in molecular mobility the motion may 
be assumed to reside either in separate atoms and mole¬ 
cules or in a fluid medium caused to undulate. A special 
rate of vibration or pulsation originally imparted to the 
portion of the fluid medium enlivens that portion of mat¬ 
ter with an individual existence, and constitutes a distinct 
substance or element. 
Again, molecular or diffusive mobility has an obvious 
bearing upon the communication of heat to gases by con¬ 
tact with liquid or solid surfaces. The impact of the 
gaseous molecule upon a surface possessing a different 
temperature appears to be the condition for the transfer¬ 
ence of heat, or the heat movement, from one to the 
other. The more rapid the molecular movement of the 
gas, the more frequent the contact, with consequent com¬ 
munication of heat. Hence, probably, the great cooling 
power of hydrogen gas as compared with air or oxygen. 
The gases named have the same specific heat for equal 
volumes ; but a hot object placed in hydrogen is really 
touched 3'8 times more frequently than it would be if 
placed in air, and 4 times more frequently than it would 
be if placed in an atmosphere of oxygen. Dalton, many 
years ago, ascribed this peculiarity of hydrogen to the 
high “ mobility ” of that gas. 
The passage of gases through colloid septa was next 
considered, and the rates of passage of certain gases 
through india-rubber compared with those of ordinary 
diffusion. These are shown in the following table :— 
Rates of 
Passage through 
Iiulia-ruhber. 
Diffusion 
Velocities. 
Nitrogen. 
1-00 
1-01 
Marsh gas .... 
2T5 
1-34 
Oxygen. 
2-55 
•95 
Hydrogen. 
5'5 
3‘80 
Carbonic acid gas . . 
13'58 
•81 
Gases may be partially separated from one another by 
passing through india-rubber just as, by passing through 
a porous plate and the stems of tobacco pipes, a partial 
analysis of mixed gases can be effected. 
Oxygen passing through india-rubber two-and-a-half 
times more rapidly than nitrogen, it was demonstrated 
that by passing air through an india-rubber bag. into the 
vacuum of a Sprengel exhauster, such air contained two- 
and-a-half times more oxygen than was originally con¬ 
tained in it. . 
The gases which pass most freely through india-rubber 
being those most freely absorbed by it, the process was 
defined as being due to— 
1. The solution of the gas in the rubber. 
2. The diffusion of the gas as a liquid through the 
thickness of the rubber. . 
3. The evaporation of the liquefied gas from the in¬ 
ternal surface of the rubber. 
4. The diffusion of the evaporated gas into the internal 
space. 
There exist, therefore, three modes of gas transmis¬ 
sion through a solid or semi-solid septum :— 
1st. By a sufficient degree of pressure gases may be 
forced bodily, i.c. in masses, through the minute channels 
of a porous septum, or, in other words, may pass through 
such a septum by transpiration, of course, in the direction 
only of the preponderating total pressure. 
2nd. As the channels of a porous septum become 
more and more minute, their resistance to the bodily 
transmission of gas becomes greater and greater, and the 
quantity of the gas forced through them less and less, 
until at last the septum is absolutely impermeable to 
transpiration under the particular pressure. But such a 
septum of which the individual capillary channels are so 
small as to offer a frictional resistance to the passage of 
gas greater than the available pressure can overcome, 
nevertheless, presents a considerable aggregate of inter¬ 
spaces through which the diffusion proper of gases, con¬ 
sequent on their innate molecular mobility, can take place 
freely in both directions. 
3rd. A septum may be quite free from pores of any 
kind or degree of minuteness, and so far be absolutely im¬ 
permeable to the transmission of gas in the form of gas. 
But it may, nevertheless, permit a considerable trans¬ 
mission of certain gases by reason of their prior solution 
or liquefaction in the substance of the septum. And 
while the mere passage of gas by transpiration or diffusion 
through a porous septum would take place in thorough 
independence of the nature of the material of the septum, 
in this last considered action, the transmission would take 
place by virtue of a sort of chemical affinity between the 
aas and the material of the septum. The selective 
absorption of the gas by the septum being a necessary 
antecedent of its transmission, it may be said that the 
cas is transmitted because it is first absorbed. Of coui.se, 
in certain transmissions, two, or all three modes of action 
may come into play simultaneously. 
The lecturer then explained the permeation of ignited 
platinum and iron to hydrogen and other gases, and the 
special property possessed by the former metal and palla¬ 
dium of allowing the hydrogen of coal gas to pass through 
them, while the marsh gas and other constituents were 
left behind. Graham’s most interesting discovery that 
metals readily absorb those gases which they freely 
transmit, led to the consideration of the occlusion of gases. 
Occlusion of Gases by Palladium and other Metals. 
The absorption of hydrogenby ignited platinum, of oxygen 
by ignited silver, and of carbonic oxide and hydrogen by iron 
were referred to, and the evolution of these gases by again 
heating the respective metals in a vacuum was shown by 
means of a Sprengel pump. The evolution of five times 
its volume of hydrogen by meteoric iron, from the Lenai to 
fall, when heated in vacuo, seems to prove the highly 
condensed nature of the atmosphere m which this gas was 
absorbed. The spectroscope has shown that hydrogen is 
one of the constituents of the atmosphere of the sun and 
