_Of NITROUS AIR._
Ever since I first read Dr. Hales's most excellent _Statical Essays_, I
was particularly struck with that experiment of his, of which an account
is given, VOL. I, p. 224. and VOL. II, p. 280. in which common air, and
air generated from the Walton pyrites, by spirit of nitre, made a turbid
red mixture, and in which part of the common air was absorbed; but I
never expected to have the satisfaction of seeing this remarkable
appearance, supposing it to be peculiar to that particular mineral.
Happening to mention this subject to the Hon. Mr. Cavendish, when I was
in London, in the spring of the year 1772, he said that he did not
imagine but that other kinds of pyrites, or the metals might answer as
well, and that probably the red appearance of the mixture depended upon
the spirit of nitre only. This encouraged me to attend to the subject;
and having no pyrites, I began with the solution of the different metals
in spirit of nitre, and catching the air which was generated in the
solution, I presently found what I wanted, and a good deal more.
Beginning with the solution of brass, on the 4th of June 1772, I first
found this remarkable species of air, only one effect of which, was
casually observed by Dr. Hales; and he gave so little attention to it,
and it has been so much unnoticed since his time, that, as far as I
know, no name has been given to it. I therefore found myself, contrary
to my first resolution, under an absolute necessity of giving a name to
this kind of air myself. When I first began to speak and write of it to
my friends, I happened to distinguish it by the name of _nitrous air_,
because I had procured it by means of spirit of nitre only; and though I
cannot say that I altogether like the term, neither myself nor any of my
friends, to whom I have applied for the purpose, have been able to hit
upon a better; so that I am obliged, after all, to content myself with
it.
I have found that this kind of air is readily procured from iron,
copper, brass, tin, silver, quicksilver, bismuth, and nickel, by the
nitrous acid only, and from gold and the regulus of antimony by _aqua
regia_. The circumstances attending the solution of each of these metals
are various, but hardly worth mentioning, in treating of the properties
of the _air_ which they yield; which, from what metal soever it is
extracted, has, as far as I have been able to observe, the very same
properties.
One of the most conspicuous properties of this kind of air is the great
diminution of any quantity of common air with which it is mixed,
attended with a turbid red, or deep orange colour, and a considerable
heat. The _smell_ of it, also, is very strong, and remarkable, but very
much resembling that of smoking spirit of nitre.
The diminution of a mixture of this and common air is not an equal
diminution of both the kinds, which is all that Dr. Hales could observe,
but of about one fifth of the common air, and as much of the nitrous air
as is necessary to produce that effect; which, as I have found by many
trials, is about one half as much as the original quantity of common
air. For if one measure of nitrous air be put to two measures of common
air, in a few minutes (by which time the effervescence will be over, and
the mixture will have recovered its transparency) there will want about
one ninth of the original two measures; and if both the kinds of air be
very pure, the diminution will still go on slowly, till in a day or two,
the whole will be reduced to one fifth less than the original quantity
of common air. This farther diminution, by long standing, I had not
observed at the time of the first publication of these papers.
I hardly know any experiment that is more adapted to amaze and surprize
than this is, which exhibits a quantity of air, which, as it were,
devours a quantity of another kind of air half as large as itself, and
yet is so far from gaining any addition to its bulk, that it is
considerably diminished by it. If, after this full saturation of common
air with nitrous air, more nitrous air be put to it, it makes an
addition equal to its own bulk, without producing the least redness, or
any other visible effect.
If the smallest quantity of common air be put to any larger quantity of
nitrous air, though the two together will not occupy so much space as
they did separately, yet the quantity will still be larger than that of
the nitrous air only. One ounce measure of common air being put to near
twenty ounce measures of nitrous air, made an addition to it of about
half an ounce measure. This being a much greater proportion than the
diminution of common air, in the former experiment, proves that part of
the diminution in the former case is in the nitrous air. Besides, it
will presently appear, that nitrous air is subject to a most remarkable
diminution; and as common air, in a variety of other cases, suffers a
diminution from one fifth to one fourth, I conclude, that in this case
also it does not exceed that proportion, and therefore that the
remainder of the diminution respects the nitrous air.
In order to judge whether the _water_ contributed to the diminution of
this mixture of nitrous and common air, I made the whole process several
times in quicksilver, using one third of nitrous, and two thirds of
common air, as before. In this case the redness continued a very long
time, and the diminution was not so great as when the mixtures had been
made in water, there remaining one seventh more than the original
quantity of common air.
This mixture stood all night upon the quicksilver; and the next morning
I observed that it was no farther diminished upon the admission of
water to it, nor by pouring it several times through the water, and
letting it stand in water two days.
Another mixture, which had stood about six hours on the quicksilver, was
diminished a little more upon the admission of water, but was never less
than the original quantity of common air. In another case however, in
which the mixture had stood but a very short time in quicksilver, the
farther diminution, which took place upon the admission of water, was
much more considerable; so that the diminution, upon the whole, was very
nearly as great as if the process had been intirely in water.
It is evident from these experiments, that the diminution is in part
owing to the absorption by the water; but that when the mixture is kept
a long time, in a situation in which there is no water to absorb any
part of it, it acquires a constitution, by which it is afterwards
incapable of being absorbed by water, or rather, there is an addition to
the quantity of air by nitrous air produced by the solution of the
quicksilver.
It will be seen, in the second part of this work, that, in the
decomposition of nitrous air by its mixture with common air, there is
nothing at hand when the process is made in quicksilver, with which the
acid that entered into its composition can readily unite.
In order to determine whether the fixed part of common air was deposited
in the diminution of it by nitrous air, I inclosed a vessel full of
lime-water in the jar in which the process was made, but it occasioned
no precipitation of the lime; and when the vessel was taken out, after
it had been in that situation a whole day, the lime was easily
precipitated by breathing into it as usual.
But though the precipitation of the lime was not sensible in this method
of making the experiment, it is sufficiently so when the whole process
is made in lime-water, as will be seen in the second part of this work;
so that we have here another evidence of the deposition of fixed air
from common air. I have made no alteration, however, in the preceding
paragraph, because it may not be unuseful, as a caution to future
experimenters.
It is exceedingly remarkable that this effervescence and diminution,
occasioned by the mixture of nitrous air, is peculiar to common air, or
_air fit for respiration_; and, as far as I can judge, from a great
number of observations, is at least very nearly, if not exactly, in
proportion to its fitness for this purpose; so that by this means the
goodness of air may be distinguished much more accurately than it can be
done by putting mice, or any other animals, to breathe in it.
This was a most agreeable discovery to me, as I hope it may be an useful
one to the public; especially as, from this time, I had no occasion for
so large a stock of mice as I had been used to keep for the purpose of
these experiments, using them only in those which required to be very
decisive; and in these cases I have seldom failed to know beforehand in
what manner they would be affected.
It is also remarkable that, on whatever account air is unfit for
respiration, this same test is equally applicable. Thus there is not the
least effervescence between nitrous and fixed air, or inflammable air,
or any species of diminished air. Also the degree of diminution being
from nothing at all to more than one third of the whole of any quantity
of air, we are, by this means, in possession of a prodigiously large
_scale_, by which we may distinguish very small degrees of difference in
the goodness of air.
I have not attended much to this circumstance, having used this test
chiefly for greater differences; but, if I did not deceive myself, I
have perceived a real difference in the air of my study, after a few
persons have been with me in it, and the air on the outside of the
house. Also a phial of air having been sent me, from the neighbourhood
of York, it appeared not to be so good as the air near Leeds; that is,
it was not diminished so much by an equal mixture of nitrous air, every
other circumstance being as nearly the same as I could contrive. It may
perhaps be possible, but I have not yet attempted it, to distinguish
some of the different winds, or the air of different times of the year,
&c. &c. by this test.
By means of this test I was able to determine what I was before in doubt
about, viz. the _kind_ as well as the _degree_ of injury done to air by
candles burning in it. I could not tell with certainty, by means of
mice, whether it was at all injured with respect to respiration; and yet
if nitrous air may be depended upon for furnishing an accurate test, it
must be rather more than one third worse than common air, and have been
diminished by the same general cause of the other diminutions of air.
For when, after many trials, I put one measure of thoroughly putrid and
highly noxious air, into the same vessel with two measures of good
wholesome air, and into another vessel an equal quantity, viz. three
measures of air in which a candle had burned out; and then put equal
quantities of nitrous air to each of them, the latter was diminished
rather more than the former.
It agrees with this observation, that _burned air_ is farther diminished
both by putrefaction, and a mixture of iron filings and brimstone; and I
therefore take it for granted by every other cause of the diminution of
air. It is probable, therefore, that burned air is air so far loaded
with phlogiston, as to be able to extinguish a candle, which it may do
long before it is fully saturated.
Inflammable air with a mixture of nitrous air burns with a green flame.
This makes a very pleasing experiment when it is properly conducted. As,
for some time, I chiefly made use of _copper_ for the generation of
nitrous air, I first ascribed this circumstance to that property of this
metal, by which it burns with a green flame; but I was presently
satisfied that it must arise from the spirit of nitre, for the effect is
the very same from which ever of the metals the nitrous air is
extracted, all of which I tried for this purpose, even silver and gold.
A mixture of oil of vitriol and spirit of nitre in equal proportions
dissolved iron, and the produce was nitrous air; but a less degree of
spirit of nitre in the mixture produced air that was inflammable, and
which burned with a green flame. It also tinged common air a little red,
and diminished it, though not much.
The diminution of common air by a mixture of nitrous air, is not so
extraordinary as the diminution which nitrous air itself is subject to
from a mixture of iron filings and brimstone, made into a paste with
water. This mixture, as I have already observed, diminishes common air
between one fifth and one fourth, but has no such effect upon any kind
of air that has been diminished, and rendered noxious by any other
process; but when it is put to a quantity of nitrous air, it diminishes
it so much, that no more than one fourth of the original quantity will
be left.
The effect of this process is generally perceived in five or six hours,
about which time the visible effervesence of the mixture begins; and in
a very short time it advances so rapidly, that in about an hour almost
the whole effect will have taken place. If it be suffered to stand a day
or two longer, the air will still be diminished farther, but only a very
little farther, in proportion to the first diminution. The glass jar,
in which the air and this mixture have been confined, has generally been
so much heated in this process, that I have not been able to touch it.
Nitrous air thus diminished has not so strong a smell as nitrous air
itself, but smells just like common air in which the same mixture has
stood; and it is not capable of being diminished any farther, by a fresh
mixture of iron and brimstone.
Common air saturated with nitrous air is also no farther diminished by
this mixture of iron filings and brimstone, though the mixture ferments
with great heat, and swells very much in it.
Plants die very soon, both in nitrous air, and also in common air
saturated with nitrous air, but especially in the former.
Neither nitrous air, nor common air saturated with nitrous air, differ
in specific gravity from common air. At least, the difference is so
small, that I could not be sure there was any; sometimes about three
pints of it seeming to be about half a grain heavier, and at other times
as much lighter than common air.
Having, among other kinds of air, exposed a quantity of nitrous air to
water out of which the air had been well boiled, in the experiment to
which I have more than once referred (as having been the occasion of
several new and important observations) I found that 19/20 of the whole
was absorbed. Perceiving, to my great surprize, that so very great a
proportion of this kind of air was miscible with water, I immediately
began to agitate a considerable quantity of it, in a jar standing in a
trough of the same kind of water; and, with about four times as much
agitation as fixed air requires, it was so far absorbed by the water,
that only about one fifth remained. This remainder extinguished flame,
and was noxious to animals.
Afterwards I diminished a pretty large quantity of nitrous air to one
eighth of its original bulk, and the remainder still retained much of
its peculiar smell, and diminished common air a little. A mouse also
died in it, but not so suddenly as it would have done in pure nitrous
air. In this operation the peculiar smell of nitrous air is very
manifest, the water being first impregnated with the air, and then
transmitting it to the common atmosphere.
This experiment gave me the hint of impregnating water with nitrous air,
in the manner in which I had before done it with fixed air; and I
presently found that distilled water would imbibe about one tenth of its
bulk of this kind of air, and that it acquired a remarkably acid and
astringent taste from it. The smell of water thus impregnated is at
first peculiarly pungent. I did not chuse to swallow any of it, though,
for any thing that I know, it may be perfectly innocent, and perhaps, in
some cases, salutary.
This kind of air is retained very obstinately by water. In an exhausted
receiver a quantity of water thus saturated emitted a whitish fume, such
as sometimes issues from bubbles of this air when it is first generated,
and also some air-bubbles; but though it was suffered to stand a long
time in this situation, it still retained its peculiar taste; but when
it had stood all night pretty near the fire, the water was become quite
vapid, and had deposited a filmy kind of matter, of which I had often
collected a considerable quantity from the trough in which jars
containing this air had stood. This I suppose to be a precipitate of the
metal, by the solution of which the nitrous air was generated. I have
not given so much attention to it as to know, with certainty, in what
circumstances this _deposit_ is made, any more than I do the matter
deposited from inflammable air above-mentioned; for I cannot get it, at
least in any considerable quantity, when I please; whereas I have often
found abundance of it, when I did not expect it at all.
The nitrous air with which I made the first impregnation of water was
extracted from copper; but when I made the impregnation with air from
quicksilver, the water had the very same taste, though the matter
deposited from it seemed to be of a different kind; for it was whitish,
whereas the other had a yellowish tinge. Except the first quantity of
this impregnated water, I could never deprive any more that I made of
its peculiar taste. I have even let some of it stand more than a week,
in phials with their mouths open, and sometimes very near the fire,
without producing any alteration in it[6].
Whether any of the spirit of nitre contained in the nitrous air be mixed
with the water in this operation, I have not yet endeavoured to
determine. This, however, may probably be the case, as the spirit of
nitre is, in a considerable degree, volatile[7].
It will perhaps be thought, that the most _useful_, if not the most
remarkable, of all the properties of this extraordinary kind of air, is
its power of preserving animal substances from putrefaction, and of
restoring those that are already putrid, which it possesses in a far
greater degree than fixed air. My first observation of this was
altogether casual. Having found nitrous air to suffer so great a
diminution as I have already mentioned by a mixture of iron filings and
brimstone, I was willing to try whether it would be equally diminished
by other causes of the diminution of common air, especially by
putrefaction; and for this purpose I put a dead mouse into a quantity of
it, and placed it near the fire, where the tendency to putrefaction was
very great. In this case there was a considerable diminution, viz. from
5-1/4 to 3-1/4; but not so great as I had expected, the antiseptic power
of the nitrous air having checked the tendency to putrefaction; for
when, after a week, I took the mouse out, I perceived, to my very great
surprize, that it had no offensive smell.
Upon this I took two other mice, one of them just killed, and the other
soft and putrid, and put them both into the same jar of nitrous air,
standing in the usual temperature of the weather, in the months of July
and August of 1772; and after twenty-five days, having observed that
there was little or no change in the quantity of the air, I took the
mice out; and, examining them, found them both perfectly sweet, even
when cut through in several places. That which had been put into the air
when just dead was quite firm; and the flesh of the other, which had
been putrid and soft, was still soft, but perfectly sweet.
In order to compare the antiseptic power of this kind of air with that
of fixed air, I examined a mouse which I had inclosed in a phial full of
fixed air, as pure as I could make it, and which I had corked very
close; but upon opening this phial in water about a month after, I
perceived that a large quantity of putrid effluvium had been generated;
for it rushed with violence out of the phial; and the smell that came
from it, the moment the cork was taken out, was insufferably offensive.
Indeed Dr. Macbride says, that he could only restore very thin pieces
of putrid flesh by means of fixed air. Perhaps the antiseptic power of
these kinds of air may be in proportion to their acidity.
If a little pains were taken with this subject, this remarkable
antiseptic power of nitrous air might possibly be applied to various
uses, perhaps to the preservation of the more delicate birds, fishes,
fruits, &c. mixing it in different proportions with common or fixed air.
Of this property of nitrous air anatomists may perhaps avail themselves,
as animal substances may by this means be preserved in their natural
soft state; but how long it will answer for this purpose, experience
only can shew.
I calcined lead and tin in the manner hereafter described in a quantity
of nitrous air, but with very little sensible effect; which rather
surprized me; as, from the result of the experiment with the iron
filings and brimstone, I had expected a very great diminution of the
nitrous air by this process; the mixture of iron filings and brimstone,
and the calcination of metals, having the same effect upon common air,
both of them diminishing it in nearly the same proportion. But though I
made the metals _fume_ copiously in nitrous air, there might be no real
_calcination_, the phlogiston not being separated, and the proper
calcination prevented by there being no _fixed_ _air_, which is
necessary to the formation of the calx, to unite with it.
Nitrous air is procured from all the proper metals by spirit of nitre,
except lead, and from all the semi-metals that I have tried, except
zinc. For this purpose I have used bismuth and nickel, with spirit of
nitre only, and regulus of antimony and platina, with _aqua regia_.
I got little or no air from lead by spirit of nitre, and have not yet
made any experiments to ascertain the nature of this solution. With zinc
I have taken a little pains.
Four penny-weights and seventeen grains of zinc dissolved in spirit of
nitre, to which as much water was added, yielded about twelve ounce
measures of air, which had, in some degree, the properties of nitrous
air, making a slight effervescence with common air, and diminishing it
about as much as nitrous air, which had been itself diminished one half
by washing in water. The smell of them both was also the same; so that I
concluded it to be the same thing, that part of the nitrous air, which
is imbibed by water, being retained in this solution.
In order to discover whether this was the case, I made the solution boil
in a sand-heat. Some air came from it in this state, which seemed to be
the same thing, with nitrous air diminished about one sixth, or one
eighth, by washing in water. When the fluid part was evaporated, there
remained a brown fixed substance, which was observed by Mr. Hellot, who
describes it, Ac. Par. 1735, M. p. 35. A part of this I threw into a
small red-hot crucible; and covering it immediately with a receiver,
standing in water, I observed that very dense red fumes rose from it,
and filled the receiver. This redness continued about as long as that
which is occasioned by a mixture of nitrous and common air; the air was
also considerably diminished within the receiver. This substance,
therefore, must certainly have contained within it the very same thing,
or principle, on which the peculiar properties of nitrous air depend.
It is remarkable, however, that though the air within the receiver was
diminished about one fifth by this process, it was itself as much
affected with a mixture of nitrous air, as common air is, and a candle
burned in it very well. This may perhaps be attributed to some effect of
the spirit of nitre, in the composition of that brown substance.
Nitrous air, I find, will be considerably diminished in its bulk by
standing a long time in water, about as much as inflammable air is
diminished in the same circumstances. For this purpose I kept for some
months a quart-bottle full of each of these kinds of air; but as
different quantities of inflammable air vary very much in this respect,
it is not improbable but that nitrous air may vary also.
From one trial that I made, I conclude that nitrous air may be kept in a
bladder much better than most other kinds of air. The air to which I
refer was kept about a fortnight in a bladder, through which the
peculiar smell of the nitrous air was very sensible for several days. In
a day or two the bladder became red, and was much contracted in its
dimensions. The air within it had lost very little of its peculiar
property of diminishing common air.
I did not endeavour to ascertain the exact quantity of nitrous air
produced from given quantities, of all the metals which yield it; but
the few observations which I did make for this purpose I shall recite in
this place:
dwt. gr.
6 0 of silver yielded 17-1/2 ounce measures.
5 19 of quicksilver 4-1/2
1 2-1/2 of copper 14-1/2
2 0 of brass 21
0 20 of iron 16
1 5 of bismuth 6
0 12 of nickel 4
FOOTNOTES:
[6] I have since found, that nitrous air has never failed to escape from
the water, which has been impregnated with it, by long exposure to the
open air.
[7] This suspicion has been confirmed by the ingenious Mr. Bewley, of
Great Massingham in Norfolk, who has discovered that the acid taste of
this water is not the necessary consequence of its impregnation with
nitrous air, but is the effect of the _acid vapour_, into which part of
this air is resolved, when it is decomposed by a mixture with common
air. This, it will be seen, exactly agrees with my own observation on
the constitution of nitrous air, in the second part of this work. A more
particular account of Mr. Bewley's observation will be given in the
_Appendix_.