_Of INFLAMMABLE AIR._
I have generally made inflammable air in the manner described by Mr.
Cavendish, in the Philosophical Transactions, from iron, zinc, or tin;
but chiefly from the two former metals, on account of the process being
the least troublesome: but when I extracted it from vegetable or animal
substances, or from coals, I put them into a gun-barrel, to the orifice
of which I luted a glass tube, or the stem of a tobacco-pipe, and to the
end of this I tied a flaccid bladder in order to catch the generated
air; or I received the air in a vessel of quicksilver, in the manner
represented Fig. 7.
There is not, I believe, any vegetable or animal substance whatever, nor
any mineral substance, that is inflammable, but what will yield great
plenty of inflammable air, when they are treated in this manner, and
urged with a strong heat; but, in order to get the most air, the heat
must be applied as suddenly, and as vehemently, as possible. For,
notwithstanding the same care be taken in luting, and in every other
respect, six or even ten times more air may be got by a sudden heat than
by a slow one, though the heat that is last applied be as intense as
that which was applied suddenly. A bit of dry oak, weighing about twelve
grains, will generally yield about a sheep's bladder full of inflammable
air with a brisk heat, when it will only give about two or three ounce
measures, if the same heat be applied to it very gradually. To what this
difference is owing, I cannot tell. Perhaps the phlogiston being
extricated more slowly may not be intirely expelled, but form another
kind of union with its base; so that charcoal made with a heat slowly
applied shall contain more phlogiston than that which is made with a
sudden heat. It may be worth while to examine the properties of the
charcoal with this view.
Inflammable air, when it is made by a quick process, has a very strong
and offensive smell, from whatever substance it be generated; but this
smell is of three different kinds, according as the air is extracted
from mineral, vegetable, or animal substances. The last is exceedingly
fetid; and it makes no difference, whether it be extracted from a bone,
or even an old and dry tooth, from soft muscular flesh; or any other
part of the animal. The burning of any substance occasions the same
smell: for the gross fume which arises from them, before they flame, is
the inflammable air they contain, which is expelled by heat, and then
readily ignited. The smell of inflammable air is the very same, as far
as I am able to perceive, from whatever substance of the same kingdom it
be extracted. Thus it makes no difference whether it be got from iron,
zinc, or tin, from any kind of wood, or, as was observed before, from
any part of an animal.
If a quantity of inflammable air be contained in a glass vessel standing
in water, and have been generated very fast, it will smell even through
the water, and this water will also soon become covered with a thin
film, assuming all the different colours. If the inflammable air have
been generated from iron, this matter will appear to be a red okre, or
the earth of iron, as I have found by collecting a considerable quantity
of it; and if it have been generated from zinc, it is a whitish
substance, which I suppose to be the calx of the metal. It likewise
settles to the bottom of the vessel, and when the water is stirred, it
has very much the appearance of wool. When water is once impregnated in
this manner, it will continue to yield this scum for a considerable time
after the air is removed from it. This I have often observed with
respect to iron.
Inflammable air, made by a violent effervescence, I have observed to be
much more inflammable than that which is made by a weak effervescence,
whether the water or the oil of vitriol prevailed in the mixture. Also
the offensive smell was much stronger in the former case than in the
latter. The greater degree of inflammability appeared by the greater
number of successive explosions, when a candle was presented to the neck
of a phial filled with it.[4] It is possible, however, that this
diminution of inflammability may, in some measure, arise from the air
continuing so much longer in the bladder when it is made very slowly;
though I think the difference is too great for this cause to have
produced the whole of it. It may, perhaps, deserve to be tried by a
different process, without a bladder.
Inflammable air is not thought to be miscible with water, and when kept
many months, seems, in general, to be as inflammable as ever. Indeed,
when it is extracted from vegetable or animal substances, a part of it
will be imbibed by the water in which it stands; but it may be presumed,
that in this case, there was a mixture of fixed air extracted from the
substance along with it. I have indisputable evidence, however, that
inflammable air, standing long in water, has actually lost all its
inflammability, and even come to extinguish flame much more than that
air in which candles have burned out. After this change it appears to be
greatly diminished in quantity, and it still continues to kill animals
the moment they are put into it.
This very remarkable fact first occurred to my observation on the
twenty-fifth of May 1771, when I was examining a quantity of inflammable
air, which had been made from zinc, near three years before. Upon this,
I immediately set by a common quart-bottle filled with inflammable air
from iron, and another equal quantity from zinc; and examining them in
the beginning of December following, that from the iron was reduced near
one half in quantity, if I be not greatly mistaken; for I found the
bottle half full of water, and I am pretty clear that it was full of air
when it was set by. That which had been produced from zinc was not
altered, and filled the bottle as at first.
Another instance of this kind occurred to my observation on the 19th of
June 1772, when a quantity of air, half of which had been inflammable
air from zinc, and half air in which mice had died, and which had been
put together the 30th of July 1771, appeared not to be in the least
inflammable, but extinguished flame, as much as any kind of air that I
had ever tried. I think that, in all, I have had four instances of
inflammable air losing its inflammability, while it stood in water.
Though air tainted with putrefaction extinguishes flame, I have not
found that animals or vegetables putrefying in inflammable air render it
less inflammable. But one quantity of inflammable air, which I had set
by in May 1771, along with the others above mentioned, had had some
putrid flesh in it; and this air had lost its inflammability, when it
was examined at the same time with the other in the December following.
The bottle in which this air had been kept, smelled exactly like very
strong Harrogate water. I do not think that any person could have
distinguished them.
I have made plants grow for several months in inflammable air made from
zinc, and also from oak; but, though the plants grew pretty well, the
air still continued inflammable. The former, indeed, was not so highly
inflammable as when it was fresh made, but the latter was quite as much
so; and the diminution of inflammability in the former case, I attribute
to some other cause than the growth of the plant.
No kind of air, on which I have yet made the experiment, will conduct
electricity; but the colour of an electric spark is remarkably different
in some different kinds of air, which seems to shew that they are not
equally good non-conductors. In fixed air, the electric spark is
exceedingly white; but in inflammable air it is of a purple, or red
colour. Now, since the most vigorous sparks are always the whitest, and,
in other cases, when the spark is red, there is reason to think that the
electric matter passes with difficulty, and with less rapidity: it is
possible that the inflammable air may contain particles which conduct
electricity, though very imperfectly; and that the whiteness of the
spark in the fixed air, may be owing to its meeting with no conducting
particles at all. When an explosion was made in a quantity of
inflammable air, it was a little white in the center, but the edges of
it were still tinged with a beautiful purple. The degree of whiteness in
this case was probably owing to the electric matter rushing with more
violence in an explosion than in a common spark.
Inflammable air kills animals as suddenly as fixed air, and, as far as
can be perceived, in the same manner, throwing them into convulsions,
and thereby occasioning present death. I had imagined that, by animals
dying in a quantity of inflammable air, it would in time become less
noxious; but this did not appear to be the case; for I killed great
number of mice in a small quantity of this air; which I kept several
months for this purpose, without its being at all sensibly mended; the
last, as well as the first mouse, dying the moment it was put into it.
I once imagined that, since fixed and inflammable air are the reverse of
one another, in several remarkable properties, a mixture of them would
make common air; and while I made the mixtures in bladders, I imagined
that I had succeeded in my attempt; but I have since found that thin
bladders do not sufficiently prevent the air that is contained in them
from mixing with the external air. Also corks will not sufficiently
confine different kinds of air, unless the phials in which they are
confined be set with their mouths downwards, and a little water lie in
the necks of them, which, indeed, is equivalent to the air standing in
vessels immersed in water. In this manner, however, I have kept
different kinds of air for several years.
Whatever methods I took to promote the mixture of fixed and inflammable
air, they were all ineffectual. I think it my duty, however, to recite
the issue of an experiment or two of this kind, in which equal mixtures
of these two kinds of air had stood near three years, as they seem to
shew that they had in part affected one another, in that long space of
time. These mixtures I examined April 27, 1771. One of them had stood in
quicksilver, and the other in a corked phial, with a little water in it.
On opening the latter in water, the water instantly rushed in, and
filled almost half of the phial, and very little more was absorbed
afterwards. In this case the water in the phial had probably absorbed a
considerable part of the fixed air, so that the inflammable air was
exceedingly rarefied; and yet the whole quantity that must have been
rendered non-elastic was ten times more than the bulk of the water, and
it has not been found that water can contain much more than its own
bulk of fixed air. But in other cases I have found the diminution of a
quantity of air, and especially of fixed air, to be much greater than I
could well account for by any kind of absorption.
The phial which had stood immersed in quicksilver had lost very little
of its original quantity of air; and being now opened in water, and left
there, along with another phial, which was just then filled, as this had
been three years before, viz. with air half inflammable and half fixed,
I observed that the quantity of both was diminished, by the absorption
of the water, in the same proportion.
Upon applying a candle to the mouths of the phials which had been kept
three years, that which had stood in quicksilver went off at one
explosion, exactly as it would have done if there had been a mixture of
common air with the inflammable. As a good deal depends upon the
apertures of the vessels in which the inflammable air is mixed, I mixed
the two kinds of air in equal proportions in the same phial, and after
letting the phial stand some days in water, that the fixed air might be
absorbed, I applied a candle to it, but it made ten or twelve explosions
(stopping the phial after each of them) before the inflammable matter
was exhausted.
The air which had been confined in the corked phial exploded in the very
same manner as an equal and fresh mixture of the two kinds of air in the
same phial, the experiment being made as soon as the fixed air was
absorbed, as before; so that in this case, the two kinds of air did not
seem to have affected one another at all.
Considering inflammable air as air united to, or loaded with phlogiston,
I exposed to it several substances, which are said to have a near
affinity with phlogiston, as oil of vitriol, and spirit of nitre (the
former for above a month), but without making any sensible alteration in
it.
I observed, however, that inflammable air, mixed with the fumes of
smoking spirit of nitre, goes off at one explosion, exactly like a
mixture of half common and half inflammable air. This I tried several
times, by throwing the inflammable air into a phial full of spirit of
nitre, with its mouth immersed in a bason containing some of the same
spirit, and then applying the flame of a candle to the mouth of the
phial, the moment that it was uncovered, after it had been taken out of
the bason.
This remarkable effect I hastily concluded to have arisen from the
inflammable air having been in part deprived of its inflammability, by
means of the stronger affinity, which the spirit of nitre had with
phlogiston, and therefore I imagined that by letting them stand longer
in contact, and especially by agitating them strongly together, I should
deprive the air of all its inflammability; but neither of these
operations succeeded, for still the air was only exploded at once, as
before.
And lastly, when I passed a quantity of inflammable air, which had been
mixed with the fumes of spirit of nitre, through a body of water, and
received it in another vessel, it appeared not to have undergone any
change at all, for it went off in several successive explosions, like
the purest inflammable air. The effect above-mentioned must, therefore,
have been owing to the fumes of the spirit of nitre supplying the place
of common air for the purpose of ignition, which is analogous to other
experiments with nitre.
Having had the curiosity, on the 25th of July 1772, to expose a great
variety of different kinds of air to water out of which the air it
contained had been boiled, without any particular view; the result was,
in several respects, altogether unexpected, and led to a variety of new
observations on the properties and affinities of several kinds of air
with respect to water. Among the rest three fourths of that which was
inflammable was absorbed by the water in about two days, and the
remainder was inflammable, but weakly so.
Upon this, I began to agitate a quantity of strong inflammable air in a
glass jar, standing in a pretty large trough of water, the surface of
which was exposed to the common air, and I found that when I had
continued the operation about ten minutes, near one fourth of the
quantity of air had disappeared; and finding that the remainder made an
effervescence with nitrous air, I concluded that it must have become fit
for respiration, whereas this kind of air is, at the first, as noxious
as any other kind whatever. To ascertain this, I put a mouse into a
vessel containing 2-1/2 ounce measures of it, and observed that it lived
in it twenty minutes, which is as long as a mouse will generally live in
the same quantity of common air. This mouse was even taken out alive,
and recovered very well. Still also the air in which it had breathed so
long was inflammable, though very weakly so. I have even found it to be
so when a mouse has actually died in it. Inflammable air thus diminished
by agitation in water, makes but one explosion on the approach of a
candle, exactly like a mixture of inflammable air with common air.
From this experiment I concluded that, by continuing the same process, I
should deprive inflammable air of all its inflammability, and this I
found to be the case; for, after a longer agitation, it admitted a
candle to burn in it, like common air, only more faintly; and indeed by
the test of nitrous air it did not appear to be near so good as common
air. Continuing the same process still farther, the air which had been
most strongly inflammable a little before, came to extinguish a candle,
exactly like air in which a candle had burned out, nor could they be
distinguished by the test of nitrous air.
I found, by repeated trials, that it was difficult to catch the time in
which inflammable air obtained from metals, in coming to extinguish
flame, was in the state of common air, so that the transition from the
one to the other must be very short. Indeed I think that in many,
perhaps in most cases, there may be no proper medium at all, the
phlogiston passing at once from that mode of union with its base which
constitutes inflammable air, to that which constitutes an air that
extinguishes flame, being so much overloaded as to admit of no more. I
readily, however, found this middle state in a quantity of inflammable
air extracted from oak, which air I had kept a year, and in which a
plant had grown, though very poorly, for some part of the time. A
quantity of this air, after being agitated in water till it was
diminished about one half, admitted a candle to burn in it exceedingly
well, and was even hardly to be distinguished from common air by the
test of nitrous air.
I took some pains to ascertain the quantity of diminution, in fresh made
and very highly-inflammable air from iron, at which it ceased to be
inflammable, and, upon the whole, I concluded that it was so when it was
diminished a little more than one half; for a quantity which was
diminished exactly one half had something inflammable in it, but in the
slightest degree imaginable. It is not improbable, however, but there
may be great differences in the result of this experiment.
Finding that water would imbibe inflammable air, I endeavoured to
impregnate water with it, by the same process by which I had made water
imbibe fixed air; but though I found that distilled water would imbibe
about one fourteenth of its bulk of inflammable air, I could not
perceive that the taste of it was sensibly altered.
FOOTNOTES:
[4] To try this, after every explosion, which immediately follows the
presenting of the flame, the mouth of the phial should be closed (I
generally do it with a finger of the hand in which I hold the phial) for
otherwise the inflammable air will continue burning, though invisibly in
the day time, till the whole be consumed.