_Of AIR infected with ANIMAL RESPIRATION, or PUTREFACTION._
That candles will burn only a certain time, in a given quantity of air
is a fact not better known, than it is that animals can live only a
certain time in it; but the cause of the death of the animal is not
better known than that of the extinction of flame in the same
circumstances; and when once any quantity of air has been rendered
noxious by animals breathing in it as long as they could, I do not know
that any methods have been discovered of rendering it fit for breathing
again. It is evident, however, that there must be some provision in
nature for this purpose, as well as for that of rendering the air fit
for sustaining flame; for without it the whole mass of the atmosphere
would, in time, become unfit for the purpose of animal life; and yet
there is no reason to think that it is, at present, at all less fit for
respiration than it has ever been. I flatter myself, however, that I
have hit upon two of the methods employed by nature for this great
purpose. How many others there may be, I cannot tell.
When animals die upon being put into air in which other animals have
died, after breathing in it as long as they could, it is plain that the
cause of their death is not the want of any _pabulum vitae,_ which has
been supposed to be contained in the air, but on account of the air
being impregnated with something stimulating to their lungs; for they
almost always die in convulsions, and are sometimes affected so
suddenly, that they are irrecoverable after a single inspiration, though
they be withdrawn immediately, and every method has been taken to bring
them to life again. They are affected in the same manner, when they are
killed in any other kind of noxious air that I have tried, viz. fixed
air, inflammable air, air filled with the fumes of brimstone, infected
with putrid matter, in which a mixture of iron filings and brimstone has
stood, or in which charcoal has been burned, or metals calcined, or in
nitrous air, &c.
As it is known that _convulsions_ weaken, and exhaust the vital powers,
much more than the most vigorous _voluntary_ action of the muscles,
perhaps these universal convulsions may exhaust the whole of what we may
call the _vis vitae_ at once, at least that the lungs may be rendered
absolutely incapable of action, till the animal be suffocated, or be
irrecoverable for want of respiration.
If a mouse (which is an animal that I have commonly made use of for the
purpose of these experiments) can stand the first shock of this
stimulus, or has been habituated to it by degrees, it will live a
considerable time in air in which other mice will die instantaneously. I
have frequently found that when a number of mice have been confined in a
given quantity of air, less than half the time that they have actually
lived in it, a fresh mouse being introduced to them has been instantly
thrown into convulsions, and died. It is evident, therefore, that if the
experiment of the Black Hole were to be repeated, a man would stand the
better chance of surviving it, who should enter at the first, than at
the last hour.
I have also observed, that young mice will always live much longer than
old ones, or than those which are full grown, when they are confined in
the same quantity of air. I have sometimes known a young mouse to live
six hours in the same circumstances in which an old mouse has not lived
one. On these accounts, experiments with mice, and, for the same reason,
no doubt, with other animals also, have a considerable degree of
uncertainty attending them; and therefore, it is necessary to repeat
them frequently, before the result can be absolutely depended upon. But
every person of feeling will rejoice with me in the discovery of
_nitrous air_, to be mentioned hereafter, which supersedes many
experiments with the respiration of animals, being a much more accurate
test of the purity of air.
The discovery of the provision in nature for restoring air, which has
been injured by the respiration of animals, having long appeared to me
to be one of the most important problems in natural philosophy, I have
tried a great variety of schemes in order to effect it. In these my
guide has generally been to consider the influences to which the
atmosphere is, in fact, exposed; and, as some of my unsuccessful trials
may be of use to those who are disposed to take pains in the farther
investigation of this subject, I shall mention the principal of them.
The noxious effluvium with which air is loaded by animal respiration, is
not absorbed by standing, without agitation; in fresh or salt water. I
have kept it many months in fresh water, when, instead of being
meliorated, it has seemed to become even more deadly, so as to require
more time to restore it, by the methods which will be explained
hereafter, than air which has been lately made noxious. I have even
spent several hours in pouring this air from one glass vessel into
another, in water, sometimes as cold, and sometimes as warm, as my hands
could bear it, and have sometimes also wiped the vessels many times,
during the course of the experiment, in order to take off that part of
the noxious matter, which might adhere to the glass vessels, and which
evidently gave them an offensive smell; but all these methods were
generally without any sensible effect. The _motion_, also, which the air
received in these circumstances, it is very evident, was of no use for
this purpose. I had not then thought of the simple, but most effectual
method of agitating air in water, by putting it into a tall jar and
shaking it with my hand.
This kind of air is not restored by being exposed to the _light_, or by
any other influence to which it is exposed, when confined in a thin
phial, in the open air, for some months.
Among other experiments, I tried a great variety of different
_effluvia_, which are continually exhaling into the air, especially of
those substances which are known to resist putrefaction; but I could not
by these means effect any melioration of the noxious quality of this
kind of air.
Having read, in the memoirs of the Imperial Society, of a plague not
affecting a particular village, in which there was a large sulphur-work,
I immediately fumigated a quantity of this kind of air; or (which will
hereafter appear to be the very same thing) air tainted with
putrefaction, with the fumes of burning brimstone, but without any
effect.
I once imagined, that the _nitrous acid_ in the air might be the general
restorative which I was in quest of; and the conjecture was favoured, by
finding that candles would burn in air extracted from saltpetre. I
therefore spent a good deal of time in attempting, by a burning glass,
and other means, to impregnate this noxious air, with some effluvium of
saltpetre, and, with the same view, introduced into it the fumes of the
smoaking spirit of nitre; but both these methods were altogether
ineffectual.
In order to try the effect of _heat_, I put a quantity of air, in which
mice had died, into a bladder, tied to the end of the stem of a
tobacco-pipe, at the other end of which was another bladder, out of
which the air was carefully pressed. I then put the middle part of the
stem into a chafing-dish of hot coals, strongly urged with a pair of
bellows; and, pressing the bladders alternately, I made the air pass
several times through the heated part of the pipe. I have also made
this kind of air very hot, standing in water before the fire. But
neither of these methods were of any use.
_Rarefaction_ and _condensation_ by instruments were also tried, but in
vain.
Thinking it possible that the _earth_ might imbibe the noxious quality
of the air, and thence supply the roots of plants with such putrescent
matter as is known to be nutritive to them, I kept a quantity of air, in
which mice had died, in a phial, one half of which was filled with fine
garden-mould; but, though it stood two months in these circumstances, it
was not the better for it.
I once imagined that, since several kinds of air cannot be long
separated from common air, by being confined in bladders, in bottles
well corked; or even closed with ground stopples, the affinity between
this noxious air and the common air might be so great, that they would
mix through a body of water interposed between them; the water
continually receiving from the one, and giving to the other, especially
as water receives some kind of impregnation from, I believe, every kind
of air to which it is contiguous; but I have seen no reason to
conclude, that a mixture of any kind of air with the common air can be
produced in this manner.
I have kept air in which mice have died, air in which candles have
burned out, and inflammable air, separated from the common air, by the
slightest partition of water that I could well make, so that it might
not evaporate in a day or two, if I should happen not to attend to them;
but I found no change in them after a month or six weeks. The
inflammable air was still inflammable, mice died instantly in the air in
which other mice had died before, and candles would not burn where they
had burned out before.
Since air tainted with animal or vegetable putrefaction is the same
thing with air rendered noxious by animal respiration, I shall now
recite the observations which I have made upon this kind of air, before
I treat of the method of restoring them.
That these two kinds of air are, in fact, the same thing, I conclude
from their having several remarkable common properties, and from their
differing in nothing that I have been able to observe. They equally
extinguish flame, they are equally noxious to animals, they are
equally, and in the same way, offensive to the smell, and they are
restored by the same means.
Since air which has passed through the lungs is the same thing with air
tainted with animal putrefaction, it is probable that one use of the
lungs is to carry off a _putrid effluvium_, without which, perhaps, a
living body might putrefy as soon as a dead one.
When a mouse putrefies in any given quantity of air, the bulk of it is
generally increased for a few days; but in a few days more it begins to
shrink up, and in about eight or ten days, if the weather be pretty
warm, it will be found to be diminished 1/6, or 1/5 of its bulk. If it
do not appear to be diminished after this time, it only requires to be
passed through water, and the diminution will not fail to be sensible. I
have sometimes known almost the whole diminution to take place, upon
once or twice passing through the water. The same is the case with air,
in which animals have breathed as long as they could. Also, air in which
candles have burned out may almost always be farther reduced by this
means.
All these processes, as I observed before, seem to dispose the compound
mass of air to part with some constituent part belonging to it (which
appears to be the _fixed air_ that enters into its constitution) and
this being miscible with water, must be brought into contact with it, in
order to mix with it to the most advantage, especially when its union
with the other constituent principles of the air is but partially
broken.
I have put mice into vessels which had their mouths immersed in
quicksilver, and observed that the air was not much contracted after
they were dead or cold; but upon withdrawing the mice, and admitting
lime water to the air, it immediately became turbid, and was contracted
in its dimensions as usual.
I tried the same thing with air tainted with putrefaction, putting a
dead mouse to a quantity of common air, in a vessel which had its mouth
immersed in quicksilver, and after a week I took the mouse out, drawing
it through the quicksilver, and observed that, for some time, there was
an apparent increase of the air perhaps about 1/20. After this, it stood
two days in the quicksilver, without any sensible alteration; and then
admitting water to it, it began to be absorbed, and continued so, till
the original quantity was diminished about 1/6. If, instead of common
water, I had made use of lime-water in this experiment, I make no doubt
but it would have become turbid.
If a quantity of lime-water in a phial be put under a glass vessel
standing in water, it will not become turbid, and provided the access of
the common air be prevented, it will continue lime-water, I do not know
how long; but if a mouse be left to putrefy in the vessel, the water
will deposit all its lime in a few days. This is owing to the fixed air
deposited by the common air, and perhaps also from more fixed air
discharged from the putrefying substances in some part of the process of
putrefaction.
The air that is discharged from putrefying substances seems, in some
cases, to be chiefly fixed air, with the addition of some other
effluvium, which has the power of diminishing common air. The
resemblance between the true putrid effluvium and fixed air in the
following experiment, which is as decisive as I can possibly contrive
it, appeared to be very great; indeed much greater than I had expected.
I put a dead mouse into a tall glass vessel, and having filled the
remainder with quicksilver, and set it, inverted, in a pot of
quicksilver, I let it stand about two months, in which time the putrid
effluvium issuing from the mouse had filled the whole vessel, and part
of the dissolved blood, which lodged upon the surface of the
quicksilver, began to be thrown out. I then filled another glass vessel,
of the same size and shape, with as pure fixed air as I could make, and
exposed them both, at the same time, to a quantity of lime-water. In
both cases the water grew turbid alike, it rose equally fast in both the
vessels, and likewise equally high; so that about the same quantity
remained unabsorbed by the water. One of these kinds of air, however,
was exceedingly sweet and pleasant, and the other insufferably
offensive; one of them also would have made an addition to any quantity
of common air, with which it had been mixed, and the other would have
diminished it. This, at least, would have been the consequence, if the
mouse itself had putrefied in any quantity of common air.
It seems to depend, in some measure, upon the _time_, and other
circumstances, in the dissolution of animal or vegetable substances,
whether they yield the proper putrid effluvium, or fixed, or inflammable
air; but the experiments which I have made upon this subject, have not
been numerous enough to enable me to decide with certainty concerning
those circumstances.
Putrid cabbage, green or boiled, infects the air in the very same manner
as putrid animal substances. Air thus tainted is equally contracted in
its dimensions, it equally extinguishes flame, and is equally noxious to
animals; but they affect the air very differently, if the heat that is
applied to them be considerable.
If beef or mutton, raw or boiled, be placed so near to the fire, that
the heat to which it is exposed shall equal, or rather exceed, that of
the blood, a considerable quantity of air will be generated in a day or
two, about 1/7th of which I have generally found to be absorbed by
water, while all the rest was inflammable; but air generated from
vegetables, in the same circumstances, will be almost all fixed air, and
no part of it inflammable. This I have repeated again and again, the
whole process being in quicksilver; so that neither common air nor
water, had any access to the substance on which the experiment was made;
and the generation of air, or effluvium of any kind, except what might
be absorbed by quicksilver, or resorbed by the substance itself, might
be distinctly noted.
A vegetable substance, after standing a day or two in these
circumstances, will yield nearly all the air that can be extracted from
it, in that degree of heat; whereas an animal substance will continue
to give more air, or effluvium, of some kind or other, with very little
alteration, for many weeks. It is remarkable, however, that though a
piece of beef or mutton, plunged in quicksilver, and kept in this degree
of heat, yield air, the bulk of which is inflammable, and contracts no
putrid smell (at least, in a day or two) a mouse treated in the same
manner, yields the proper putrid effluvium, as indeed the smell
sufficiently indicates.
That the putrid effluvium will mix with water seems to be evident from
the following experiment. If a mouse be put into a jar full of water,
standing with its mouth inverted in another vessel of water, a
considerable quantity of elastic matter (and which may, therefore, be
called _air_) will soon be generated, unless the weather be so cold as
to check all putrefaction. After a short time, the water contracts an
extremely fetid and offensive smell, which seems to indicate that the
putrid effluvium pervades the water, and affects the neighbouring air;
and since, after this, there is often no increase of the air, that seems
to be the very substance which is carried off through the water, as fast
as it is generated; and the offensive smell is a sufficient proof that
it is not fixed air. For this has a very agreeable flavour, whether it
be produced by fermentation, or extracted from chalk by oil of vitriol;
affecting not only the mouth, but even the nostrils; with a pungency
which is peculiarly pleasing to a certain degree, as any person may
easily satisfy himself, who will chuse to make the experiment.
If the water in which the mouse was immersed, and which is saturated
with the putrid air, be changed, the greater part of the putrid air,
will, in a day or two, be absorbed, though the mouse continues to yield
the putrid effluvium as before; for as soon as this fresh water becomes
saturated with it, it begins to be offensive to the smell, and the
quantity of the putrid air upon its surface increases as before. I kept
a mouse producing putrid air in this manner for the space of several
months.
Six ounce measures of air not readily absorbed by water, appeared to
have been generated from one mouse, which had been putrefying eleven
days in confined air, before it was put into a jar which was quite
filled with water, for the purpose of this observation.
Air thus generated from putrid mice standing in water, without any
mixture of common air, extinguishes flame, and is noxious to animals,
but not more so than common air only tainted with putrefaction. It is
exceedingly difficult and tedious to collect a quantity of this putrid
air, not miscible in water, so very great a proportion of what is
collected being absorbed by the water in which it is kept; but what that
proportion is, I have not endeavoured to ascertain. It is probably the
same proportion that that part of fixed air, which is not readily
absorbed by water, bears to the rest; and therefore this air, which I at
first distinguished by the name of _the putrid effluvium_, is probably
the same with fixed air, mixed with the phlogistic matter, which, in
this and other processes, diminishes common air.
Though a quantity of common air be diminished by any substance
putrefying in it, I have not yet found the same effect to be produced by
a mixture of putrid air with common air; but, in the manner in which I
have hitherto made the experiment, I was obliged to let the putrid air
pass through a body of water, which might instantly absorb the
phlogistic matter that diminished the common air.
Insects of various kinds live perfectly well in air tainted with animal
or vegetable putrefaction, when a single inspiration of it would have
instantly killed any other animal. I have frequently tried the
experiment with flies and butterflies. The _aphides_ also will thrive as
well upon plants growing in this kind of air, as in the open air. I
have even been frequently obliged to take plants out of the putrid air
in which they were growing, on purpose to brush away the swarms of these
insects which infected them; and yet so effectually did some of them
conceal themselves, and so fast did they multiply, in these
circumstances, that I could seldom keep the plants quite clear of them.
When air has been freshly and strongly tainted with putrefaction, so as
to smell through the water, sprigs of mint have presently died, upon
being put into it, their leaves turning black; but if they do not die
presently, they thrive in a most surprizing manner. In no other
circumstances have I ever seen vegetation so vigorous as in this kind of
air, which is immediately fatal to animal life. Though these plants have
been crouded in jars filled with this air, every leaf has been full of
life; fresh shoots have branched out in various directions, and have
grown much faster than other similar plants, growing in the same
exposure in common air.
This observation led me to conclude, that plants, instead of affecting
the air in the same manner with animal respiration, reverse the effects
of breathing, and tend to keep the atmosphere sweet and wholesome, when
it is become noxious, in consequence of animals either living and
breathing, or dying and putrefying in it.
In order to ascertain this, I took a quantity of air, made thoroughly
noxious, by mice breathing and dying in it, and divided it into two
parts; one of which I put into a phial immersed in water; and to the
other (which was contained in a glass jar, standing in water) I put a
sprig of mint. This was about the beginning of August 1771, and after
eight or nine days, I found that a mouse lived perfectly well in that
part of the air, in which the sprig of mint had grown, but died the
moment it was put into the other part of the same original quantity of
air; and which I had kept in the very same exposure, but without any
plant growing in it.
This experiment I have several times repeated; sometimes using air in
which animals had breathed and died, and at other times using air,
tainted with vegetable or animal putrefaction; and generally with the
same success.
Once, I let a mouse live and die in a quantity of air which had been
noxious, but which had been restored by this process, and it lived
nearly as long as I conjectured it might have done in an equal quantity
of fresh air; but this is so exceedingly various, that it is not easy to
form any judgment from it; and in this case the symptom of _difficult
respiration_ seemed to begin earlier than it would have done in common
air.
Since the plants that I made use of manifestly grow and thrive in putrid
air; since putrid matter is well known to afford proper nourishment for
the roots of plants; and since it is likewise certain that they receive
nourishment by their leaves as well as by their roots, it seems to be
exceedingly probable, that the putrid effluvium is in some measure
extracted from the air, by means of the leaves of plants, and therefore
that they render the remainder more fit for respiration.
Towards the end of the year some experiments of this kind did not answer
so well as they had done before, and I had instances of the relapsing of
this restored air to its former noxious state. I therefore suspended my
judgment concerning the efficacy of plants to restore this kind of
noxious air, till I should have an opportunity of repeating my
experiments, and giving more attention to them. Accordingly I resumed
the experiments in the summer of the year 1772, when I presently had the
most indisputable proof of the restoration of putrid air by vegetation;
and as the fact is of some importance, and the subsequent variation in
the state of this kind of air is a little remarkable, I think it
necessary to relate some of the facts pretty circumstantially.
The air, on which I made the first experiments, was rendered exceedingly
noxious by mice dying in it on the 20th of June. Into a jar nearly
filled with one part of this air, I put a sprig of mint, while I kept
another part of it in a phial, in the same exposure; and on the 27th of
the same month, and not before, I made a trial of them, by introducing a
mouse into a glass vessel, containing 2-1/2 ounce measures filled with
each kind of air; and I noted the following facts.
When the vessel was filled with the air in which the mint had grown, a
very large mouse lived five minutes in it, before it began to shew any
sign of uneasiness. I then took it out, and found it to be as strong and
vigorous as when it was first put in; whereas in that air which had been
kept in the phial only, without a plant growing in it, a younger mouse
continued not longer than two or three seconds, and was taken out quite
dead. It never breathed after, and was immediately motionless. After
half an hour, in which time the larger mouse (which I had kept alive,
that the experiment might be made on both the kinds of air with the very
same animal) would have been sufficiently recruited, supposing it to
have received any injury by the former experiment, was put into the same
vessel of air; but though it was withdrawn again, after being in it
hardly one second, it was recovered with difficulty, not being able to
stir from the place for near a minute. After two days, I put the same
mouse into an equal quantity of common air, and observed that it
continued seven minutes without any sign of uneasiness; and being very
uneasy after three minutes longer, I took it out. Upon the whole, I
concluded that the restored air wanted about one fourth of being as
wholesome as common air. The same thing also appeared when I applied the
test of nitrous air.
In the seven days, in which the mint was growing in this jar of noxious
air, three old shoots had extended themselves about three inches, and
several new ones had made their appearance in the same time. Dr.
Franklin and Sir John Pringle happened to be with me, when the plant had
been three or four days in this state, and took notice of its vigorous
vegetation, and remarkably healthy appearance in that confinement.
On the 30th of the same month, a mouse lived fourteen minutes, breathing
naturally all the time, and without appearing to be much uneasy, till
the last two minutes, in the vessel containing two ounce measures and a
half of air which had been rendered noxious, by mice breathing in it
almost a year before, and which, I had found to be most highly noxious
on the 19th of this month, a plant having grown in it, but not
exceedingly well, these eleven days; on which account I had deferred
making the trial so long. The restored air was affected by a mixture of
nitrous air, almost as much as common air.
As this putrid air was thus easily restored to a considerable degree of
fitness for respiration, by plants growing in it, I was in hopes that by
the same means it might in time be so much more perfectly restored, that
a candle would burn in it; and for this purpose I kept plants growing in
the jars which contained this air till the middle of August following,
but did not take sufficient care to pull out all the old and rotten
leaves. The plants, however, had grown, and looked so well upon the
whole, that I had no doubt but that the air must constantly have been in
a mending state; when I was exceedingly surprized to find, on the 24th
of that month, that though the air in one of the jars had not grown
worse, it was no better; and that the air in the other jar was so much
worse than it had been, that a mouse would have died in it in a few
seconds. It also made no effervescence with nitrous air, as it had done
before.
Suspecting that the same plant might be capable of restoring putrid air
to a certain degree only, or that plants might have a contrary tendency
in some stages of their growth, I withdrew the old plant, and put a
fresh one in its place; and found that, after seven days, the air was
restored to its former wholesome state. This fact I consider as a very
remarkable one, and well deserving of a farther investigation, as it may
throw more light upon the principles of vegetation. It is not, however,
a single fact; for I had several instances of the same kind in the
preceding year; but it seemed so very extraordinary, that air should
grow worse by the continuance of the same treatment by which it had
grown better, that, whenever I observed it, I concluded that I had not
taken sufficient care to satisfy myself of its previous restoration.
That plants are capable of perfectly restoring air injured by
respiration, may, I think, be inferred with certainty from the perfect
restoration, by this means, of air which had passed through my lungs, so
that a candle would burn in it again, though it had extinguished flame
before, and apart of the same original quantity of air still continued
to do so. Of this one instance occurred in the year 1771, a sprig of
mint having grown in a jar of this kind of air, from the 25th of July to
the 17th of August following; and another trial I made, with the same
success, the 7th of July 1772, the plant having grown in it from the
29th of June preceding. In this case also I found that the effect was
not owing to any virtue in the leaves of mint; for I kept them
constantly changed in a quantity of this kind of air, for a considerable
time, without making any sensible alteration in it.
These proofs of a partial restoration of air by plants in a state of
vegetation, though in a confined and unnatural situation, cannot but
render it highly probable, that the injury which is continually done to
the atmosphere by the respiration of such a number of animals, and the
putrefaction of such masses of both vegetable and animal matter, is, in
part at least, repaired by the vegetable creation. And, notwithstanding
the prodigious mass of air that is corrupted daily by the
above-mentioned causes; yet, if we consider the immense profusion of
vegetables upon the face of the earth, growing in places, suited to
their nature, and consequently at full liberty to exert all their
powers, both inhaling and exhaling, it can hardly be thought, but that
it may be a sufficient counterbalance to it, and that the remedy is
adequate to the evil.
Dr. Franklin, who, as I have already observed, saw some of my plants in
a very flourishing state, in highly noxious air, was pleased to express
very great satisfaction with the result of the experiments. In his
answer to the letter in which I informed him of it, he says,
"That the vegetable creation should restore the air which is spoiled by
the animal part of it, looks like a rational system, and seems to be of
a piece with the rest. Thus fire purifies water all the world over. It
purifies it by distillation, when it raises it in vapours, and lets it
fall in rain; and farther still by filtration, when, keeping it fluid,
it suffers that rain to percolate the earth. We knew before that putrid
animal substances were converted into sweet vegetables, when mixed with
the earth, and applied as manure; and now, it seems, that the same
putrid substances, mixed with the air, have a similar effect. The strong
thriving state of your mint in putrid air seems to shew that the air is
mended by taking something from it, and not by adding to it." He adds,
"I hope this will give some check to the rage of destroying trees that
grow near houses, which has accompanied our late improvements in
gardening, from an opinion of their being unwholesome. I am certain,
from long observation, that there is nothing unhealthy in the air of
woods; for we Americans have every where our country habitations in the
midst of woods, and no people on earth enjoy better health, or are more
prolific."
Having rendered inflammable air perfectly innoxious by continued
_agitation in a trough of water_, deprived of its air, I concluded that
other kinds of noxious air might be restored by the same means; and I
presently found that this was the case with putrid air, even of more
than a year's standing. I shall observe once for all, that this process
has never failed to restore any kind of noxious air on which I have
tried it, viz. air injured by respiration or putrefaction, air infected
with the fumes of burning charcoal, and of calcined metals, air in which
a mixture of iron filings and brimstone, that in which paint made of
white lead and oil has stood, or air which has been diminished by a
mixture of nitrous air. Of the remarkable effect which this process has
on nitrous air itself, an account will be given in its proper place.
If this process be made in water deprived of air, either by the
air-pump, by boiling, or by distillation, or if fresh rain-water be
used, the air will always be diminished by the agitation; and this is
certainly the fairest method of making the experiment. If the water be
fresh pump-water, there will always be an increase of the air by
agitation, the air contained in the water being set loose, and joining
that which is in the jar. In this case, also, the air has never failed
to be restored; but then it might be suspected that the melioration was
produced by the addition of some more wholesome ingredient. As these
agitations were made in jars with wide mouths, and in a trough which had
a large surface exposed to the common air, I take it for granted that
the noxious effluvia, whatever they be, were first imbibed by the water,
and thereby transmitted to the common atmosphere. In some cases this was
sufficiently indicated by the disagreeable smell which attended the
operation.
After I had made these experiments, I was informed that an ingenious
physician and philosopher had kept a fowl alive twenty-four hours, in a
quantity of air in which another fowl of the same size had not been able
to live longer than an hour, by contriving to make the air, which it
breathed, pass through no very large quantity of acidulated water, the
surface of which was not exposed to the common air; and that even when
the water was not acidulated, the fowl lived much longer than it could
have done, if the air which it breathed had not been drawn through the
water.
As I should not have concluded that this experiment would have succeeded
so well, from any observations that I had made upon the subject, I took
a quantity of air in which mice had died, and agitated it very strongly,
first in about five times its own quantity of distilled water, in the
manner in which I had impregnated water with fixed air; but though the
operation was continued a long time, it made no sensible change in the
properties of the air. I also repeated the operation with pump-water,
but with as little effect. In this case, however, though the air was
agitated in a phial, which had a narrow neck, the surface of the water
in the bason was considerably large, and exposed to the common
atmosphere, which must have tended a little to favour the experiment.
In order to judge more precisely of the effect of these different
methods of agitating air, I transferred the very noxious air, which I
had hot been able to amend in the least degree by the former method,
into an open jar, standing in a trough of water; and when I had agitated
it till it was diminished about one third, I found it to be better than
air in which candles had burned out, as appeared by the test of the
nitrous air; and a mouse lived in 2-1/2 ounce measures of it a quarter
of an hour, and was not sensibly affected the first ten or twelve
minutes.
In order to determine whether the addition of any _acid_ to the water,
would make it more capable of restoring putrid air, I agitated a
quantity of it in a phial containing very strong vinegar; and after that
in _aqua fortis_, only half diluted with water; but by neither of these
processes was the air at all mended, though the agitation was repeated,
at intervals, during a whole day, and it was moreover allowed to stand
in that situation all night.
Since, however, water in these experiments must have imbibed and
retained a certain portion of the noxious effluvia, before they could be
transmitted to the external air, I do not think it improbable but that
the agitation of the sea and large lakes may be of some use for the
purification of the atmosphere, and the putrid matter contained in water
may be imbibed by aquatic plants, or be deposited in some other manner.
Having found, by several experiments above-mentioned that the proper
putrid effluvium is something quite distinct from fixed air, and
finding, by the experiments of Dr. Macbride, that fixed air corrects
putrefaction; it occured to me, that fixed air, and air tainted with
putrefaction, though equally, noxious when separate, might make a
wholesome mixture, the one, correcting the other; and I was confirmed in
this opinion by, I believe, not less than fifty or sixty instances, in
which air, that had been made in the highest degree noxious, by
respiration or putrefaction, was so far sweetened, by a mixture of about
four times as much fixed air, that afterwards mice lived in it
exceedingly well, and in some cases almost as long as in common air. I
found it, indeed, to be more difficult to restore _old_ putrid air by
this means; but I hardly ever failed to do it, when the two kinds of air
had stood a long time together; by which I mean about a fortnight or
three weeks.
The reason why I do not absolutely conclude that the restoration of air
in these cases was the effect of fixed air, is that, when I made a trial
of the mixture, I sometimes agitated the two kinds of air pretty
strongly together, in a trough of water, or at least passed it several
times through water, from one jar to another, that the superfluous fixed
air might be absorbed, not suspecting at that time that the agitation
could have any other effect. But having since found that very violent,
and especially long-continued agitation in water, without any mixture of
fixed air, never failed to render any kind of noxious air in some
measure fit for respiration (and in one particular instance the mere
transferring of the air from one vessel to another through the water,
though for a much longer time than I ever used for the mixtures of air,
was of considerable use for the same purpose) I began to entertain some
doubt of the efficacy of fixed air in this case. In some cases also the
mixture of fixed air had by no means so much effect on the putrid air
as, from the generality of my observations, I should have expected.
I was always aware, indeed, that it might be said, that, the residuum of
fixed air not being very noxious, such an addition must contribute to
mend the putrid air; but, in order to obviate this objection, I once
mixed the residuum of as much fixed air as I had found, by a variety of
trials, to be sufficient to restore a given quantity of putrid air, with
an equal quantity of that air, without making any sensible melioration
of it.
Upon the whole, I am inclined to think that this process could hardly
have succeeded so well as it did with me, and in so great a number of
trials, unless fixed air have some tendency to correct air tainted with
respiration or putrefaction; and it is perfectly agreeable to the
analogy of Dr. Macbride's discoveries, and may naturally be expected
from them, that it should have such an effect.
By a mixture of fixed air I have made wholesome the residuum of air
generated by putrefaction only, from mice plunged in water. This, one
would imagine, _a priori_, to be the most noxious of all kinds of air.
For if common air only tainted with putrefaction be so deadly, much more
might one expect that air to be so, which was generated from
putrefaction only; but it seems to be nothing more than common air (or
at least that kind of fixed air which is not absorbed by water) tainted
with putrefaction, and therefore requires no other process to sweeten
it. In this case, however, we seem to have an instance of the generation
of genuine common air, though mixed with something that is foreign to
it. Perhaps the residuum of fixed air may be another instance of the
same nature, and also the residuum of inflammable air, and of nitrous
air, especially nitrous air loaded with phlogiston, after long agitation
in water.
Fixed air is equally diffused through the whole mass of any quantity of
putrid air with which it is mixed: for dividing the mixture into two
equal parts, they were reduced in the same proportion by passing through
water. But this is also the case with some of the kinds of air which
will not incorporate, as inflammable air, and air in which brimstone has
burned.
If fixed air tend to correct air which has been injured by animal
respiration or putrefaction, _lime kilns_, which discharge great
quantities of fixed air, may be wholesome in the neighbourhood of
populous cities, the atmosphere of which must abound with putrid
effluvia. I should think also that physicians might avail themselves of
the application of fixed air in many putrid disorders, especially as it
may be so easily administered by way of _clyster_, where it would often
find its way to much of the putrid matter. Nothing is to be apprehended
from the distention of the bowels by this kind of air, since it is so
readily absorbed by any fluid or moist substance.
Since fixed air is not noxious _per se_, but, like fire, only in excess,
I do not think it at all hazardous to attempt to _breathe_ it. It is
however easily conveyed into the _stomach_, in natural or artificial
Pyrmont water, in briskly-fermenting liquors, or a vegetable diet. It
is even possible, that a considerable quantity of fixed air might be
imbibed by the absorbing vessels of the skin, if the whole body, except
the head, should be suspended over a vessel of strongly-fermenting
liquor; and in some putrid disorders this treatment might be very
salutary. If the body was exposed quite naked, there would be very
little danger from the cold in this situation, and the air having freer
access to the skin might produce a greater effect. Being no physician, I
run no risk by throwing out these random, and perhaps whimsical
proposals.[5]
Having communicated my observations on fixed air, and especially my
scheme of applying it by way of _clyster_ in putrid disorders, to Mr.
Hey, an ingenious surgeon in Leeds a case presently occurred, in which
he had an opportunity of giving it a trial; and mentioning it to Dr.
Hird and Dr. Crowther, two physicians who attended the patient, they
approved the scheme, and it was put in execution; both by applying the
fixed air by way of clyster, and at the same time making the patient
drink plentifully of liquors strongly impregnated with it. The event
was such, that I requested Mr. Hey to draw up a particular account of
the case, describing the whole of the treatment, that the public might
be satisfied that this new application of fixed air is perfectly safe,
and also, have an opportunity of judging how far it had the effect which
I expected from it; and as the application is new, and not unpromising,
I shall subjoin his letter to me on the subject, by way of _Appendix_ to
these papers.
When I began my inquires into the properties of different kinds of air,
I engaged my friend Dr. Percival to attend to the _medicinal uses_ of
them, being sensible that his knowledge of philosophy as well as of
medicine would give him a singular advantage for this purpose. The
result of his observations I shall also insert in the Appendix.
FOOTNOTES:
[5] Some time after these papers were first printed, I was pleased to
find the same proposal in _Dr. Alexander's Experimental Essays_.