atmospherical air. For this purpose, it is burnt in a graduated tube,
called an _Eudiometer_ (PLATE XI. fig. 2.), and from the quantity of air
which the phosphorus absorbs, the proportion of oxygen in the air
examined is deduced; for the phosphorus will absorb all the oxygen, and
the nitrogen alone will remain.
EMILY.
And the more oxygen is contained in the atmosphere, the purer,
I suppose, it is esteemed?
MRS. B.
Certainly. Phosphorus, when melted, combines with a great variety of
substances. With sulphur it forms a compound so extremely combustible,
that it immediately takes fire on coming in contact with the air. It is
with this composition that phosphoric matches are prepared, which kindle
as soon as they are taken out of their case and are exposed to the air.
EMILY.
I have a box of these curious matches; but I have observed, that in very
cold weather, they will not take fire without being previously rubbed.
MRS. B.
By rubbing them you raise their temperature; for, you know, friction is
one of the means of extricating heat.
EMILY.
Will phosphorus combine with hydrogen gas, as sulphur does?
MRS. B.
Yes; and the compound gas which results from this combination has a
smell still more fetid than the sulphuretted hydrogen; it resembles that
of garlic.
The _phosphoretted hydrogen gas_ has this remarkable peculiarity, that
it takes fire spontaneously in the atmosphere, at any temperature. It is
thus, probably, that are produced those transient flames, or flashes of
light, called by the vulgar _Will-of-the Whisp_, or more properly
_Ignes-fatui_, which are often seen in church-yards, and places where
the putrefactions of animal matter exhale phosphorus and hydrogen gas.
CAROLINE.
Country people, who are so much frightened by those appearances, would
soon be reconciled to them, if they knew from what a simple cause they
proceed.
MRS. B.
There are other combinations of phosphorus that have also very singular
properties, particularly that which results from its union with lime.
EMILY.
Is there any name to distinguish the combination of two substances, like
phosphorus and lime, neither of which are oxygen, and which cannot
therefore produce either an oxyd or an acid?
MRS. B.
The names of such combinations are composed from those of their
ingredients, merely by a slight change in their termination. Thus the
combination of sulphur with lime is called a _sulphuret_, and that of
phosphorus, a _phosphuret of lime_. This latter compound, I was going to
say, has the singular property of decomposing water, merely by being
thrown into it. It effects this by absorbing the oxygen of water, in
consequence of which bubbles of hydrogen gas ascend, holding in solution
a small quantity of phosphorus.
EMILY.
These bubbles then are _phosphoretted hydrogen gas_?
MRS. B.
Yes; and they produce the singular appearance of a flash of fire issuing
from water, as the bubbles kindle and detonate on the surface of the
water, at the instant that they come in contact with the atmosphere.
CAROLINE.
Is not this effect nearly similar to that produced by the combination of
phosphorus and sulphur, or, more properly speaking, the _phosphuret of
sulphur_?
MRS. B.
Yes; but the phenomenon appears more extraordinary in this case, from
the presence of water, and from the gaseous form of the combustible
compound. Besides, the experiment surprises by its great simplicity. You
only throw a piece of phosphoret of lime into a glass of water, and
bubbles of fire will immediately issue from it.
CAROLINE.
Cannot we try the experiment?
MRS. B.
Very easily: but we must do it in the open air; for the smell of the
phosphorated hydrogen gas is so extremely fetid, that it would be
intolerable in the house. But before we leave the room, we may produce,
by another process, some bubbles of the same gas, which are much less
offensive.
There is in this little glass retort a solution of potash in water;
I add to it a small piece of phosphorus. We must now heat the retort
over the lamp, after having engaged its neck under water--you see it
begins to boil; in a few minutes bubbles will appear, which take fire
and detonate as they issue from the water.
CAROLINE.
There is one--and another. How curious it is! --But I do not understand
how this is produced.
MRS. B.
It is the consequence of a display of affinities too complicated,
I fear, to be made perfectly intelligible to you at present.
In a few words, the reciprocal action of the potash, phosphorus,
caloric, and water are such, that some of the water is decomposed, and
the hydrogen gas thereby formed carries off some minute particles of
phosphorus, with which it forms phosphoretted hydrogen gas, a compound
which spontaneously takes fire at almost any temperature.
EMILY.
What is that circular ring of smoke which slowly rises from each bubble
after its detonation?
MRS. B.
It consists of water and phosphoric acid in vapour, which are produced
by the combustion of hydrogen and phosphorus.
CONVERSATION IX.
ON CARBON.
CAROLINE.
To-day, Mrs. B., I believe we are to learn the nature and properties of
CARBON. This substance is quite new to me; I never heard it mentioned
before.
MRS. B.
Not so new as you imagine; for carbon is nothing more than charcoal in a
state of purity, that is to say, unmixed with any foreign ingredients.
CAROLINE.
But charcoal is made by art, Mrs. B., and a body consisting of one
simple substance cannot be fabricated?
MRS. B.
You again confound the idea, of making a simple body, with that of
separating it from a compound. The chemical processes by which a simple
body is obtained in a state of purity, consist in _unmaking_ the
compound in which it is contained, in order to separate from it the
simple substance in question. The method by which charcoal is usually
obtained, is, indeed, commonly called _making_ it; but, upon
examination, you will find this process to consist simply in separating
it from other substances with which it is found combined in nature.
Carbon forms a considerable part of the solid matter of all organised
bodies; but it is most abundant in the vegetable creation, and it is
chiefly obtained from wood. When the oil and water (which are other
constituents of vegetable matter) are evaporated, the black, porous,
brittle substance that remains, is charcoal.
CAROLINE.
But if heat be applied to the wood in order to evaporate the oil and
water, will not the temperature of the charcoal be raised so as to make
it burn; and if it combines with oxygen, can we any longer call it pure?
MRS. B.
I was going to say, that, in this operation, the air must be excluded.
CAROLINE.
How then can the vapour of the oil and water fly off?
MRS. B.
In order to produce charcoal in its purest state (which is, even then,
but a less imperfect sort of carbon), the operation should be performed
in an earthen retort. Heat being applied to the body of the retort, the
evaporable part of the wood will escape through its neck, into which no
air can penetrate as long as the heated vapour continues to fill it. And
if it be wished to collect these volatile products of the wood, this can
easily be done by introducing the neck of the retort into the water-bath
apparatus, with which you are acquainted. But the preparation of common
charcoal, such as is used in kitchens and manufactures, is performed on
a much larger scale, and by an easier and less expensive process.
EMILY.
I have seen the process of making common charcoal. The wood is ranged on
the ground in a pile of a pyramidical form, with a fire underneath; the
whole is then covered with clay, a few holes only being left for the
circulation of air.
MRS. B.
These holes are closed as soon as the wood is fairly lighted, so that
the combustion is checked, or at least continues but in a very imperfect
manner; but the heat produced by it is sufficient to force out and
volatilize, through the earthy cover, most part of the oily and watery
principles of the wood, although it cannot reduce it to ashes.
EMILY.
Is pure carbon as black as charcoal?
MRS. B.
The purest charcoal we can prepare is so; but chemists have never yet
been able to separate it entirely from hydrogen. Sir H. Davy says, that
the most perfect carbon that is prepared by art contains about five per
cent. of hydrogen; he is of opinion, that if we could obtain it quite
free from foreign ingredients, it would be metallic, in common with
other simple substances.
But there is a form in which charcoal appears, that I dare say will
surprise you. --This ring, which I wear on my finger, owes its
brilliancy to a small piece of carbon.
CAROLINE.
Surely, you are jesting, Mrs. B.?
EMILY.
I thought your ring was diamond?
MRS. B.
It is so. But diamond is nothing more than carbon in a crystallized
state.
EMILY.
That is astonishing! Is it possible to see two things apparently more
different than diamond and charcoal?
CAROLINE.
It is, indeed, curious to think that we adorn ourselves with jewels of
charcoal!
MRS. B.
There are many other substances, consisting chiefly of carbon, that are
remarkably white. Cotton, for instance, is almost wholly carbon.
CAROLINE.
That, I own, I could never have imagined! --But pray, Mrs. B., since it
is known of what substance diamond and cotton are composed, why should
they not be manufactured, or imitated, by some chemical process, which
would render them much cheaper, and more plentiful than the present mode
of obtaining them?
MRS. B.
You might as well, my dear, propose that we should make flowers and
fruit, nay, perhaps even animals, by a chemical process; for it is known
of what these bodies consist, since every thing which we are acquainted
with in nature is formed from the various simple substances that we have
enumerated. But you must not suppose that a knowledge of the component
parts of a body will in every case enable us to imitate it. It is much
less difficult to decompose bodies, and discover of what materials they
are made, than it is to recompose them. The first of these processes is
called _analysis_, the last _synthesis_. When we are able to ascertain
the nature of a substance by both these methods, so that the result of
one confirms that of the other, we obtain the most complete knowledge of
it that we are capable of acquiring. This is the case with water, with
the atmosphere, with most of the oxyds, acids, and neutral salts, and
with many other compounds. But the more complicated combinations of
nature, even in the mineral kingdom, are in general beyond our reach,
and any attempt to imitate organised bodies must ever prove fruitless;
their formation is a secret that rests in the bosom of the Creator. You
see, therefore, how vain it would be to attempt to make cotton by
chemical means. But, surely, we have no reason to regret our inability
in this instance, when nature has so clearly pointed out a method of
obtaining it in perfection and abundance.
CAROLINE.
I did not imagine that the principle of life could be imitated by the
aid of chemistry; but it did not appear to me ridiculous to suppose that
chemists might attain a perfect imitation of inanimate nature.
MRS. B.
They have succeeded in this point in a variety of instances; but, as you
justly observe, the principle of life, or even the minute and intimate
organisation of the vegetable kingdom, are secrets that have almost
entirely eluded the researches of philosophers; nor do I imagine that
human art will ever be capable of investigating them with complete
success.
EMILY.
But diamond, since it consists of one simple unorganised substance,
might be, one would think, perfectly imitable by art?
MRS. B.
It is sometimes as much beyond our power to obtain a simple body in a
state of perfect purity, as it is to imitate a complicated combination;
for the operations by which nature separates bodies are frequently as
inimitable as those which she uses for their combination. This is the
case with carbon; all the efforts of chemists to separate it entirely
from other substances have been fruitless, and in the purest state in
which it can be obtained by art, it still retains a portion of hydrogen,
and probably of some other foreign ingredients. We are ignorant of the
means which nature employs to crystallize it. It may probably be the
work of ages, to purify, arrange, and unite the particles of carbon in
the form of diamond. Here is some charcoal in the purest state we can
procure it: you see that it is a very black, brittle, light, porous
substance, entirely destitute of either taste or smell. Heat, without
air, produces no alteration in it, as it is not volatile; but, on the
contrary, it invariably remains at the bottom of the vessel after all
the other parts of the vegetable are evaporated.
EMILY.
Yet carbon is, no doubt, combustible, since you say that charcoal would
absorb oxygen if air were admitted during its preparation?
CAROLINE.
Unquestionably. Besides, you know, Emily, how much it is used in
cooking. But pray what is the reason that charcoal burns without smoke,
whilst a wood fire smokes so much?
MRS. B.
Because, in the conversion of wood into charcoal, the volatile particles
of the former have been evaporated.
CAROLINE.
Yet I have frequently seen charcoal burn with flame; therefore it must,
in that case, contain some hydrogen.
MRS. B.
Very true; but you must recollect that charcoal, especially that which
is used for common purposes, is not perfectly pure. It generally retains
some remains of the various other component parts of vegetables, and
hydrogen particularly, which accounts for the flame in question.
CAROLINE.
But what becomes of the carbon itself during its combustion?
MRS. B.
It gradually combines with the oxygen of the atmosphere, in the same way
as sulphur and phosphorus, and, like those substances, it is converted
into a peculiar acid, which flies off in a gaseous form. There is this
difference, however, that the acid is not, in this instance, as in the
two cases just mentioned, a mere condensable vapour, but a permanent
elastic fluid, which always remains in the state of gas, under any
pressure and at any temperature. The nature of this acid was first
ascertained by Dr. Black, of Edinburgh; and, before the introduction of
the new nomenclature, it was called _fixed air_. It is now distinguished
by the more appropriate name of _carbonic acid gas_.
EMILY.
Carbon, then, can be volatilized by burning, though, by heat alone, no
such effect is produced?
MRS. B.
Yes; but then it is no longer simple carbon, but an acid of which carbon
forms the basis. In this state, carbon retains no more appearance of
solidity or corporeal form, than the basis of any other gas. And you
may, I think, from this instance, derive a more clear idea of the basis
of the oxygen, hydrogen, and nitrogen gases, the existence of which, as
real bodies, you seemed to doubt, because they were not to be obtained
simply in a solid form.
EMILY.
That is true; we may conceive the basis of the oxygen, and of the other
gases, to be solid, heavy substances, like carbon; but so much expanded
by caloric as to become invisible.
CAROLINE.
But does not the carbonic acid gas partake of the blackness of charcoal?
MRS. B.
Not in the least. Blackness, you know, does not appear to be essential
to carbon, and it is pure carbon, and not charcoal, that we must
consider as the basis of carbonic acid. We shall make some carbonic
acid, and, in order to hasten the process, we shall burn the carbon in
oxygen gas.
EMILY.
But do you mean then to burn diamond?
MRS. B.
Charcoal will answer the purpose still better, being softer and more
easy to inflame; besides the experiments on diamond are rather
expensive.
CAROLINE.
But is it possible to burn diamond?
MRS. B.
Yes, it is; and in order to effect this combustion, nothing more is
required than to apply a sufficient degree of heat by means of the
blow-pipe, and of a stream of oxygen gas. Indeed it is by burning
diamond that its chemical nature has been ascertained. It has long been
known as a combustible substance, but it is within these few years only
that the product of its combustion has been proved to be pure carbonic
acid. This remarkable discovery is due to Mr. Tennant.
Now let us try to make some carbonic acid. --Will you, Emily, decant
some oxygen gas from this large jar into the receiver in which we are to
burn the carbon; and I shall introduce this small piece of charcoal,
with a little lighted tinder, which will be necessary to give the first
impulse to the combustion.
EMILY.
I cannot conceive how so small a piece of tinder, and that but just
lighted, can raise the temperature of the carbon sufficiently to set
fire to it; for it can produce scarcely any sensible heat, and it hardly
touches the carbon.
MRS. B.
The tinder thus kindled has only heat enough to begin its own
combustion, which, however, soon becomes so rapid in the oxygen gas, as
to raise the temperature of the charcoal sufficiently for this to burn
likewise, as you see is now the case.
EMILY.
I am surprised that the combustion of carbon is not more brilliant; it
does not give out near so much light or caloric as phosphorus, or
sulphur. Yet since it combines with so much oxygen, why is not a
proportional quantity of light and heat disengaged from the
decomposition of the oxygen gas, and the union of its electricity with
that of the charcoal?
MRS. B.
It is not surprising that less light and heat should be liberated in
this than in almost any other combustion, since the oxygen, instead of
entering into a solid or liquid combination, as it does in the
phosphoric and sulphuric acids, is employed in forming another elastic
fluid; it therefore parts with less of its caloric.
EMILY.
True; and, on second consideration, it appears, on the contrary,
surprising that the oxygen should, in its combination with carbon,
retain a sufficient portion of caloric to maintain both substances in a
gaseous state.
CAROLINE.
We may then judge of the degree of solidity in which oxygen is combined
in a burnt body, by the quantity of caloric liberated during its
combustion?
MRS. B.
Yes; provided that you take into the account the quantity of oxygen
absorbed by the combustible body, and observe the proportion which the
caloric bears to it.
CAROLINE.
But why should the water, after the combustion of carbon, rise in the
receiver, since the gas within it retains an aëriform state?
MRS. B.
Because the carbonic acid gas is gradually absorbed by the water; and
this effect would be promoted by shaking the receiver.
EMILY.
The charcoal is now extinguished, though it is not nearly consumed; it
has such an extraordinary avidity for oxygen, I suppose, that the
receiver did not contain enough to satisfy the whole.
MRS. B.
That is certainly the case; for if the combustion were performed in the
exact proportions of 28 parts of carbon to 72 of oxygen, both these
ingredients would disappear, and 100 parts of carbonic acid would be
produced.
CAROLINE.
Carbonic acid must be a very strong acid, since it contains so great a
proportion of oxygen?
MRS. B.
That is a very natural inference; yet it is erroneous. For the carbonic
is the weakest of all the acids. The strength of an acid seems to depend
upon the nature of its basis, and its mode of combination, as well as
upon the proportion of the acidifying principle. The same quantity of
oxygen that will convert some bodies into strong acids, will only be
sufficient simply to oxydate others.
CAROLINE.
Since this acid is so weak, I think chemists should have called it the
_carbonous_, instead of the _carbonic_ acid.
EMILY.
But, I suppose, the carbonous acid is still weaker, and is formed by
burning carbon in atmospherical air.
MRS. B.
It has been lately discovered, that carbon may be converted into a gas,
by uniting with a smaller proportion of oxygen; but as this gas does not
possess any acid properties, it is no more than an oxyd; it is called
_gaseous oxyd of carbon_.
CAROLINE.
Pray is not carbonic acid a very wholesome gas to breathe, as it
contains so much oxygen?
MRS. B.
On the contrary, it is extremely pernicious. Oxygen, when in a state of
combination with other substances, loses, in almost every instance, its
respirable properties, and the salubrious effects which it has on the
animal economy when in its unconfined state. Carbonic acid is not only
unfit for respiration, but extremely deleterious if taken into the
lungs.
EMILY.
You know, Caroline, how very unwholesome the fumes of burning charcoal
are reckoned.
CAROLINE.
Yes; but, to confess the truth, I did not consider that a charcoal fire
produced carbonic acid gas. --Can this gas be condensed into a liquid?
MRS. B.
No: for, as I told you before, it is a permanent elastic fluid. But
water can absorb a certain quantity of this gas, and can even be
impregnated with it, in a very strong degree, by the assistance of
agitation and pressure, as I am going to show you. I shall decant some
carbonic acid gas into this bottle, which I fill first with water, in
order to exclude the atmospherical air; the gas is then introduced
through the water, which you see it displaces, for it will not mix with
it in any quantity, unless strongly agitated, or allowed to stand over
it for some time. The bottle is now about half full of carbonic acid
gas, and the other half is still occupied by the water. By corking the
bottle, and then violently shaking it, in this way, I can mix the gas
and water together. --Now will you taste it?
EMILY.
It has a distinct acid taste.
CAROLINE.
Yes, it is sensibly sour, and appears full of little bubbles.
MRS. B.
It possesses likewise all the other properties of acids, but, of course,
in a less degree than the pure carbonic acid gas, as it is so much
diluted by water.
This is a kind of artificial Seltzer water. By analysing that which is
produced by nature, it was found to contain scarcely any thing more than
common water impregnated with a certain proportion of carbonic acid gas.
We are, therefore, able to imitate it, by mixing those proportions of
water and carbonic acid. Here, my dear, is an instance, in which, by a
chemical process, we can exactly copy the operations of nature; for the
artificial Seltzer waters can be made in every respect similar to those
of nature; in one point, indeed, the former have an advantage, since
they may be prepared stronger, or weaker, as occasion requires.
CAROLINE.
I thought I had tasted such water before. But what renders it so brisk
and sparkling?
MRS. B.
This sparkling, or effervescence, as it is called, is always occasioned
by the action of an elastic fluid escaping from a liquid; in the
artifical Seltzer water, it is produced by the carbonic acid, which
being lighter than the water in which it was strongly condensed, flies
off with great rapidity the instant the bottle is uncorked; this makes
it necessary to drink it immediately. The bubbling that took place in
this bottle was but trifling, as the water was but very slightly
impregnated with carbonic acid. It requires a particular apparatus to
prepare the gaseous artificial mineral waters.
EMILY.
If, then, a bottle of Seltzer water remains for any length of time
uncorked, I suppose it returns to the state of common water?
MRS. B.
The whole of the carbonic acid gas, or very nearly so, will soon
disappear; but there is likewise in Seltzer water a very small quantity
of soda, and of a few other saline or earthy ingredients, which will
remain in the water, though it should be kept uncorked for any length of
time.
CAROLINE.
I have often heard of people drinking soda-water. Pray what sort of
water is that?
MRS. B.
It is a kind of artificial Seltzer water, holding in solution, besides
the gaseous acid, a particular saline substance, called soda, which
imparts to the water certain medicinal qualities.
CAROLINE.
But how can these waters be so wholesome, since carbonic acid is so
pernicious?
MRS. B.
A gas, we may conceive, though very prejudicial to breathe, may be
beneficial to the stomach. --But it would be of no use to attempt
explaining this more fully at present.
CAROLINE.
Are waters never impregnated with other gases?
MRS. B.