cub. in.
Oxygene 71,5
Nitrogene 45,6
Carbonic acid 7,9
So that comparing the quantities, it appears, that 11,4 of oxygene and
1,4 of nitrogene, were consumed in this experiment, and 3,8 of carbonic
acid produced.
I was much surprised at the small quantity of oxygene that had been
consumed in this experiment. This quantity was less than that expended
during the respiration of atmospheric air for half a minute: the
portion of carbonic acid evolved was likewise smaller. I could detect
no source of inaccuracy, and it was difficult to suppose that the
greater depth and fulness of the inspirations could make any difference.
E. 2. I now respired at the same temperature, after a full expiration,
162 cubic inches of gas, composed of 133 oxygene and 20 nitrogene for
two minutes, imitating as much as possible, the natural respiration.
After the experiment, they filled a space equal to 123 cubic inches.
And when the analysis and calculations had been made as in the last
experiment, it appeared that 57 cubic inches of oxygene, and 2 of
nitrogene had been absorbed, whilst 21 cubic inches of carbonic acid
had been formed.
Now from the estimations in the last section, it appears that 63 cubic
inches of oxygene are consumed, and about 52 cubic inches of carbonic
acid produced every two minutes during the natural respiration of
common air. So that supposing the experiment accurate, 6 cubic inches
of oxygene less are absorbed, and 30 cubic inches less of carbonic acid
produced every minute, when oxygene nearly pure is respired, than when
atmospheric air is respired.
Both these experiments were made in the morning, at a time when I was
in perfect health; so that there could be apparently no source of error
from accidental circumstances.
The uncommon and unexpected nature of the results, made me however,
very sceptical concerning them; and before I would draw any inferences,
I resolved to ascertain the comparative consumption of atmospheric air
and oxygene by the smaller quadrupeds, for which purpose, I made the
following experiment.
E. 3. Of two strong and healthy small mice, apparently of the same
breed, and exactly similar.
One was introduced into a jar containing 10 cubic inches and half of
oxygene, and 3 cubic inches of nitrogene, and made to rest on a bit of
cheese.
The other was introduced into a jar containing fifteen cubic inches and
half of atmospheric air, and made to rest in the same manner on cheese.
The mouse in oxygene began apparently to suffer in about half an hour,
and occasionally panted very much; in about an hour he lay down on his
side as if dying. The jars were often agitated, that the gases might be
well mingled.
The mouse in atmospheric air became very feeble in 40 minutes, and at
the end of 50 minutes was taken out through the mercury alive, but
unable to stand.
The mouse in oxygene was taken out in the same manner after an hour and
quarter, alive, but motionless, and breathing very deeply.
The gas in the jars was examined. That in the oxygene jar filled a
space exactly equal to 12,7 cubic inches, and analised, was found to
consist of 1,7 carbonic acid, 2,6 of nitrogene, and 8,4 of oxygene. So
that absolutely, 2,1 cubic inches of oxygene and,4 of nitrogene had
been consumed, and 1,7 of carbonic acid produced.
The gas in the atmospheric air jar was diminished nearly to 14,4, and
consisted of 2,1 carbonic acid, 1,4 oxygene; and 10,9 nitrogene. So
that 2,7 of oxygene and,5 of nitrogene, had been consumed by the mouse;
and 2,1 of carbonic acid produced.
Hence it appears, that the mouse in atmospheric air consumed nearly
one third more oxygene and produced nearly one fourth more carbonic
acid in respiration in 55 minutes, than the other in an hour and
quarter in oxygene. And if we consider the perpetual diminution of the
oxygene of the atmospheric air; from which at last it became almost
incapable of supporting the life of the animal; we may conclude, that
the quantity of oxygene consumed by it, had the air been perpetually
renovated, would have been much more considerable.
I design very shortly, to repeat these experiments, and to make others
on the comparative consumption of oxygene and atmospheric air, by the
larger quadrupeds. Whatever may be the results, I hope to be able to
ascertain from them, why pure oxygene is incapable of supporting life.
VIII. _Observations on the changes effected in the blood, by
atmospheric air and oxygene._
From the experiments of Mr. Cigna and Dr. Priestley,[202] it appears
that the coagulum of the venous blood becomes florid at its surface
when exposed to the atmosphere, though covered and defended from the
immediate contact of air by a very thick stratum of serum.
[202] Dr. Priestley found that it likewise became florid at the surface
when covered by milk; but that it underwent little or no alteration of
color under water and most other fluids.—Vol. 3. p. 372.
Hence it is evident, that serum is capable of dissolving either the
whole compound atmospheric air, or the oxygene of it.
Supposing what indeed is most probable from numerous analogies, that
it dissolves the whole compound; it would follow, that the coloring
of the coagulum of blood under serum, depended upon the decomposition
of the atmospheric air condensed in the serum, the oxygene[203] of it
combining with the red particles, and the nitrogene either remaining
dissolved in the fluid, or being liberated through it into the
atmosphere.
Now the circulating blood consists of red particles, floating in and
diffused through serum and coagulable lymph.
[203] There are many analogous decompositions. Dr. Priestley noticed
(and I have often made the observation) that green oxide of iron, or
the precipitate from pale green sulphate of iron by caustic alkali,
became red at the surface, when covered by a thick stratum of water. In
my experiments on the green muriate and sulphate of iron, I observed
that part of some dark oxide of iron which was at the bottom of a
trough of water 9 inches deep, became red at the surface nearly in the
same time as another portion of the same precipitation that was exposed
to the atmosphere. This oxygenation must depend upon the decomposition
of atmospheric air constantly dissolved by the water.
In natural respiration, the red particles are rendered of a brighter
tinge during the passage of the blood through the pulmonary veins. And
as we have seen in the last sections, during respiration atmospheric
air is decomposed; all the oxygene of it consumed, _apparently_ a small
portion of the nitrogene lost, and a considerable quantity of carbonic
acid produced.
It seems therefore reasonable to suppose, that the whole compound
atmospheric air passing through the moist coats of the vessels is first
dissolved by the serum of the venous blood, and in its condensed state,
decomposed by the affinity of the red particles for its oxygene; the
greater part of the nitrogene being liberated unaltered; but a minute
portion of it possibly remaining condensed in the serum and coagulable
lymph, and passing with them into the left chamber of the heart.
From the experiments on the respiration of nitrous oxide and hydrogene,
it appears that a certain portion of the carbonic acid produced in
respiration, is evolved from the venous blood; but as a much greater
quantity is generated during the respiration of common air and oxygene,
than during that of hydrogene in equal times, it is not impossible but
that some portion of it may be formed by the combination of charcoal in
the red particles with the oxygene dissolved in the serum; but this can
only be determined by farther experiments.
Supposing that no part of the water evolved in solution by the expired
gas of common air is formed immediately in respiration, it will follow
that a very considerable quantity of oxygene must be constantly
_combined_ with the red particles, even allowing the consumption of
a certain portion of it to form carbonic acid; for the carbonic acid
evolved, rarely amounts to more than three fourths of the volume of the
oxygene consumed.
Perhaps the serum of the blood is capable of dissolving a larger
quantity of atmospheric air than of pure oxygene. On this supposition,
it would be easy to explain the smaller consumption of oxygene in the
experiments in the last section.