for all the alkalies and alkaline earths, that these are always found in
nature in the state of carbonats. Combined with lime, this acid forms
chalk, which may be considered as the basis of all kinds of marbles, and
calcareous stones. From these substances carbonic acid is easily
separated, as it adheres so slightly to its combinations, that the
carbonats are all decomposable by any of the other acids. I can easily
show you how I obtained this gas; I poured some diluted sulphuric acid
over pulverised marble in this bottle (the same which we used the other
day to prepare hydrogen gas), and the gas escaped through the tube
connected with it; the operation still continues, as you may easily
perceive--
EMILY.
Yes, it does; there is a great fermentation in the glass vessel. What
singular commotion is excited by the sulphuric acid taking possession of
the lime, and driving out the carbonic acid!
CAROLINE.
But did the carbonic acid exist in a gaseous state in the marble?
MRS. B.
Certainly not; the acid, when in a state of combination, is capable of
existing in a solid form.
CAROLINE.
Whence, then, does it obtain the caloric necessary to convert it into
gas?
MRS. B.
It may be supplied in this case from the mixture of sulphuric acid and
water, which produces an evolution of heat, even greater than is
required for the purpose; since, as you may perceive by touching the
glass vessel, a considerable quantity of the caloric disengaged becomes
sensible. But a supply of caloric may be obtained also from a diminution
of capacity for heat, occasioned by the new combination which takes
place; and, indeed, this must be the case when other acids are employed
for the disengagement of carbonic acid gas, which do not, like the
sulphuric, produce heat on being mixed with water. Carbonic acid may
likewise be disengaged from its combinations by heat alone, which
restores it to its gaseous state.
CAROLINE.
It appears to me very extraordinary that the same gas, which is produced
by the burning of wood and coals, should exist also in such bodies as
marble, and chalk, which are incombustible substances.
MRS. B.
I will not answer that objection, Caroline, because I think I can put
you in a way of doing it yourself. Is carbonic acid combustible?
CAROLINE.
Why, no--because it is a body that has been already burnt; it is carbon
only, and not the acid, that is combustible.
MRS. B.
Well, and what inference do you draw from this?
CAROLINE.
That carbonic acid cannot render the bodies with which it is united
combustible; but that simple carbon does, and that it is in this
elementary state that it exists in wood, coals, and a great variety of
other combustible bodies. --Indeed, Mrs. B., you are very ungenerous;
you are not satisfied with convincing me that my objections are
frivolous, but you oblige me to prove them so myself.
MRS. B.
You must confess, however, that I make ample amends for the detection of
error, when I enable you to discover the truth. You, understand, now,
I hope, that carbonic acid is equally produced by the decomposition of
chalk, or by the combustion of charcoal. These processes are certainly
of a very different nature; in the first case the acid is already
formed, and requires nothing more than heat to restore it to its gaseous
state; whilst, in the latter, the acid is actually made by the process
of combustion.
CAROLINE.
I understand it now perfectly. But I have just been thinking of another
difficulty, which, I hope, you will excuse my not being able to remove
myself. How does the immense quantity of calcareous earth, which is
spread all over the globe, obtain the carbonic acid with which it is
combined?
MRS. B.
The question is, indeed, not very easy to answer; but I conceive that
the general carbonisation of calcareous matter may have been the effect
of a general combustion, occasioned by some revolution of our globe, and
producing an immense supply of carbonic acid, with which the calcareous
matter became impregnated; or that this may have been effected by a
gradual absorption of carbonic acid from the atmosphere. --But this
would lead us to discussions which we cannot indulge in, without
deviating too much from our subject.
EMILY.
How does it happen that we do not perceive the pernicious effects of the
carbonic acid which is floating in the atmosphere?
MRS. B.
Because of the state of very great dilution in which it exists there.
But can you tell me, Emily, what are the sources which keep the
atmosphere constantly supplied with this acid?
EMILY.
I suppose the combustion of wood, coals, and other substances, that
contain carbon.
MRS. B.
And also the breath of animals.
CAROLINE.
The breath of animals! I thought you said that this gas was not at all
respirable, but on the contrary, extremely poisonous.
MRS. B.
So it is; but although animals cannot breathe in carbonic acid gas, yet,
in the process of respiration, they have the power of forming this gas
in their lungs; so that the air which we _expire_, or reject from the
lungs, always contains a certain proportion of carbonic acid, which is
much greater than that which is commonly found in the atmosphere.
CAROLINE.
But what is it that renders carbonic acid such a deadly poison?
MRS. B.
The manner in which this gas destroys life, seems to be merely by
preventing the access of respirable air; for carbonic acid gas, unless
very much diluted with common air, does not penetrate into the lungs, as
the windpipe actually contracts and refuses it admittance. --But we must
dismiss this subject at present, as we shall have an opportunity of
treating of respiration much more fully, when we come to the chemical
functions of animals.
EMILY.
Is carbonic acid as destructive to the life of vegetables as it is to
that of animals?
MRS. B.
If a vegetable be completely immersed in it, I believe it generally
proves fatal to it; but mixed in certain proportions with atmospherical
air, it is, on the contrary, very favourable to vegetation.
You remember, I suppose, our mentioning the mineral waters, both natural
and artificial, which contain carbonic acid gas?
CAROLINE.
You mean the Seltzer water?
MRS. B.
That is one of those which are the most used; there are, however,
a variety of others into which carbonic acid enters as an ingredient:
all these waters are usually distinguished by the name of _acidulous_ or
_gaseous mineral waters_.
The class of salts called _carbonats_ is the most numerous in nature; we
must pass over them in a very cursory manner, as the subject is far too
extensive for us to enter on it in detail. The state of carbonat is the
natural state of a vast number of minerals, and particularly of the
alkalies and alkaline earths, as they have so great an attraction for
the carbonic acid, that they are almost always found combined with it;
and you may recollect that it is only by separating them from this acid,
that they acquire that causticity and those striking qualities which I
have formerly described. All marbles, chalks, shells, calcareous spars,
and lime-stones of every description, are neutral salts, in which
_lime_, their common basis, has lost all its characteristic properties.
EMILY.
But if all these various substances are formed by the union of lime with
carbonic acid, whence arises their diversity of form and appearance?
MRS. B.
Both from the different proportions of their component parts, and from a
variety of foreign ingredients which may be occasionally blended with
them: the veins and colours of marbles, for instance, proceed from a
mixture of metallic substances; silex and alumine also frequently enter
into these combinations. The various carbonats, therefore, that I have
enumerated, cannot be considered as pure unadulterated neutral salts,
although they certainly belong to that class of bodies.
CONVERSATION XIX.
ON THE BORACIC, FLUORIC, MURIATIC, AND OXYGENATED MURIATIC ACIDS; AND ON
MURIATS. --ON IODINE AND IODIC ACID.
MRS. B.
We now come to the three remaining acids with simple bases, the compound
nature of which, though long suspected, has been but recently proved.
The chief of these is the muriatic; but I shall first describe the two
others, as their bases have been obtained more distinctly than that of
the muriatic acid.
You may recollect I mentioned the BORACIC ACID. This is found very
sparingly in some parts of Europe, but for the use of manufactures we
have always received it from the remote country of Thibet, where it is
found in some lakes, combined with soda. It is easily separated from the
soda by sulphuric acid, and appears in the form of shining scales, as
you see here.
CAROLINE.
I am glad to meet with an acid which we need not be afraid to touch; for
I perceive, from your keeping it in a piece of paper, that it is more
innocent than our late acquaintance, the sulphuric and nitric acids.
MRS. B.
Certainly; but being more inert, you will not find its properties so
interesting. However, its decomposition, and the brilliant spectacle it
affords when its basis again unites with oxygen, atones for its want of
other striking qualities.
Sir H. Davy succeeded in decomposing the boracic acid, (which had till
then been considered as undecompoundable,) by various methods. On
exposing this acid to the Voltaic battery, the positive wire gave out
oxygen, and on the negative wire was deposited a black substance, in
appearance resembling charcoal. This was the basis of the acid, which
Sir H. Davy has called _Boracium_, or _Boron_.
The same substance was obtained in more considerable quantities, by
exposing the acid to a great heat in an iron gun-barrel.
A third method of decomposing the boracic acid consisted in burning
potassium in contact with it in vacuo. The potassium attracts the oxygen
from the acid, and leaves its basis in a separate state.
The recomposition of this acid I shall show you, by burning some of its
basis, which you see here, in a retort full of oxygen gas. The heat of a
candle is all that is required for this combustion.--
EMILY.
The light is astonishingly brilliant, and what beautiful sparks it
throws out!
MRS. B.
The result of this combustion is the boracic acid, the nature of which,
you see, is proved both by analytic and synthetic means. Its basis has
not, it is true, a metallic appearance; but it makes very hard alloys
with other metals.
EMILY.
But pray, Mrs. B., for what purpose is the boracic acid used in
manufactures?
MRS. B.
Its principal use is in conjunction with soda, that is, in the state of
_borat of soda_, which in the arts is commonly called borax. This salt
has a peculiar power of dissolving metallic oxyds, and of promoting the
fusion of substances capable of being melted; it is accordingly employed
in various metallic arts; it is used, for example, to remove the oxyd
from the surface of metals, and is often employed in the assaying of
metallic ores.
Let us now proceed to the FLUORIC ACID. This acid is obtained from a
substance which is found frequently in mines, and particularly in those
of Derbyshire, called _fluor_, a name which it acquired from the
circumstance of its being used to render the ores of metals more fluid
when heated.
CAROLINE.
Pray is not this the Derbyshire spar, of which so many ornaments are
made?
MRS. B.
The same; but though it has long been employed for a variety of
purposes, its nature was unknown until Scheele, the great Swedish
chemist, discovered that it consisted of lime united with a peculiar
acid, which obtained the name of _fluoric acid_. It is easily separated
from the lime by the sulphuric acid, and unless condensed in water,
ascends in the form of gas. A very peculiar property of this acid is its
union with siliceous earths, which I have already mentioned. If the
distillation of this acid is performed in glass vessels, they are
corroded, and the siliceous part of the glass comes over, united with
the gas; if water is then admitted, part of the silex is deposited, as
you may observe in this jar.
CAROLINE.
I see white flakes forming on the surface of the water; is that silex?
MRS. B.
Yes it is. This power of corroding glass has been used for engraving, or
rather etching, upon it. The glass is first covered with a coat of wax,
through which the figures to be engraved are to be scratched with a pin;
then pouring the fluoric acid over the wax, it corrodes the glass where
the scratches have been made.
CAROLINE.
I should like to have a bottle of this acid, to make engravings.
MRS. B.
But you could not have it in a _glass_ bottle, for in that case the acid
would be saturated with silex, and incapable of executing an engraving;
the same thing would happen were the acid kept in vessels of porcelain
or earthen-ware; this acid must therefore be both prepared and preserved
in vessels of silver.
If it be distilled from fluor spar and vitriolic acid, in silver or
leaden vessels, the receiver being kept very cold during the
distillation, it assumes the form of a dense fluid, and in that state is
the most intensely corrosive substance known. This seems to be the acid
combined with a little water. It may be called _hydro-fluoric acid_; and
Sir H. Davy has been led, from some late experiments on the subject, to
consider _pure_ fluoric acid as a compound of a certain unknown
principle, which he calls _fluorine_, with hydrogen.
Sir H. Davy has also attempted to decompose the fluoric acid by burning
potassium in contact with it; but he has not yet been able by this or
any other method, to obtain its basis in a distinct separate state.
We shall conclude our account of the acids with that of the MURIATIC
ACID, which is perhaps the most curious and interesting of all of them.
It is found in nature combined with soda, lime, and magnesia. _Muriat of
soda_ is the common sea-salt, and from this substance the acid is
usually disengaged by means of the sulphuric acid. The natural state of
the muriatic acid is that of an invisible permanent gas, at the common
temperature of the atmosphere; but it has a remarkably strong attraction
for water, and assumes the form of a whitish cloud whenever it meets any
moisture to combine with. This acid is remarkable for its peculiar and
very pungent smell, and possesses, in a powerful degree, most of the
acid properties. Here is a bottle containing muriatic acid in a liquid
state.
CAROLINE.
And how is it liquefied?
MRS. B.
By impregnating water with it; its strong attraction for water makes it
very easy to obtain it in a liquid form. Now, if I open the phial, you
may observe a kind of vapour rising from it, which is muriatic acid gas,
of itself invisible, but made apparent by combining with the moisture of
the atmosphere.
EMILY.
Have you not any of the pure muriatic acid gas?
MRS. B.
This jar is full of that acid in its gaseous state--it is inverted over
mercury instead of water, because, being absorbable by water, this gas
cannot be confined by it. --I shall now raise the jar a little on one
side, and suffer some of the gas to escape. --You see that it
immediately becomes visible in the form of a cloud.
EMILY.
It must be, no doubt, from its uniting with the moisture of the
atmosphere, that it is converted into this dewy vapour.
MRS. B.
Certainly; and for the same reason, that is to say, its extreme
eagerness to unite with water, this gas will cause snow to melt as
rapidly as an intense fire.
This acid proved much more refractory when Sir H. Davy attempted to
decompose it than the other two undecompounded acids. It is singular
that potassium will burn in muriatic acid, and be converted into potash,
without decomposing the acid, and the result of this combustion is a
_muriat of potash_; for the potash, as soon as it is regenerated,
combines with the muriatic acid.
CAROLINE.
But how can the potash be regenerated if the muriatic acid does not
oxydate the potassium?
MRS. B.
The potassium, in this process, obtains oxygen from the moisture with
which the muriatic acid is always combined, and accordingly hydrogen,
resulting from the decomposition of the moisture, is invariably evolved.
EMILY.
But why not make these experiments with dry muriatic acid?
MRS. B.
Dry acids cannot be acted on by the Voltaic battery, because acids are
non-conductors of electricity, unless moistened. In the course of a
number of experiments which Sir H. Davy made upon acids in a state of
dryness, he observed that the presence of water appeared always
necessary to develop the acid properties, so that acids are not even
capable of reddening vegetable blues if they have been carefully
deprived of moisture. This remarkable circumstance led him to suspect,
that water, instead of oxygen, may be the acidifying principle; but this
he threw out rather as a conjecture than as an established point.
Sir H. Davy obtained very curious results from burning potassium in a
mixture of phosphorus and muriatic acid, and also of sulphur and
muriatic acid; the latter detonates with great violence. All his
experiments, however, failed in presenting to his view the basis of the
muriatic acid, of which he was in search; and he was at last induced to
form an opinion respecting the nature of this acid, which I shall
presently explain.
EMILY.
Is this acid susceptible of different degrees of oxygenation?
MRS. B.
Yes, for though we cannot deoxygenate this acid, yet we may add oxygen
to it.
CAROLINE.
Why, then, is not the least degree of oxygenation of the acid called the
_muriatous_, and the higher degree the _muriatic_ acid?
MRS. B.
Because, instead of becoming, like other acids, more dense, and more
acid by an addition of oxygen, it is rendered on the contrary more
volatile, more pungent, but less acid, and less absorbable by water.
These circumstances, therefore, seem to indicate the propriety of making
an exception to the nomenclature. The highest degree of oxygenation of
this acid has been distinguished by the additional epithet of
_oxygenated_, or, for the sake of brevity, _oxy_, so that it is called
the _oxygenated_, or _oxy-muriatic acid_. This likewise exists in a
gaseous form, at the temperature of the atmosphere; it is also
susceptible of being absorbed by water, and can be congealed, or
solidified, by a certain degree of cold.
EMILY.
And how do you obtain the oxy-muriatic acid?
MRS. B.
In various ways; but it may be most conveniently obtained by distilling
liquid muriatic acid over oxyd of manganese, which supplies the acid
with the additional oxygen. One part of the acid being put into a
retort, with two parts of the oxyd of manganese, and the heat of a lamp
applied, the gas is soon disengaged, and may be received over water, as
it is but sparingly absorbed by it. --I have collected some in this
jar--
CAROLINE.
It is not invisible, like the generality of gases; for it is of a
yellowish colour.
MRS. B.
The muriatic acid extinguishes flame, whilst, on the contrary, the
oxy-muriatic makes the flame larger, and gives it a dark red colour. Can
you account for this difference in the two acids?
EMILY.
Yes, I think so; the muriatic acid will not supply the flame with the
oxygen necessary for its support; but when this acid is further
oxygenated, it will part with its additional quantity of oxygen, and in
this way support combustion.
MRS. B.
That is exactly the case; indeed the oxygen added to the muriatic acid,
adheres so slightly to it, that it is separated by mere exposure to the
sun’s rays. This acid is decomposed also by combustible bodies, many of
which it burns, and actually inflames, without any previous increase of
temperature.
CAROLINE.
That is extraordinary, indeed! I hope you mean to indulge us with some
of these experiments?
MRS. B.
I have prepared several glass jars of oxy-muriatic acid gas for that
purpose. In the first we shall introduce some Dutch gold leaf. --Do you
observe that it takes fire?
EMILY.
Yes, indeed it does--how wonderful it is! It became immediately red hot,
but was soon smothered in a thick vapour.
CAROLINE.
What a disagreeable smell!
MRS. B.
We shall try the same experiment with phosphorus in another jar of this
acid. --You had better keep your handkerchief to your nose when I open
it--now let us drop into it this little piece of phosphorus--
CAROLINE.
It burns really; and almost as brilliantly as in oxygen gas! But, what
is most extraordinary, these combustions take place without the metal or
phosphorus being previously lighted, or even in the least heated.
MRS. B.
All these curious effects are owing to the very great facility with
which this acid yields oxygen to such bodies as are strongly disposed to
combine with it. It appears extraordinary indeed to see bodies, and
metals in particular, melted down and inflamed, by a gas without any
increase of temperature, either of the gas, or of the combustible. The
phenomenon, however, is, you see, well accounted for.
EMILY.
Why did you burn a piece of Dutch gold leaf rather than a piece of any
other metal?
MRS. B.
Because, in the first place, it is a composition of metals (consisting
chiefly of copper) which burns readily; and I use a thin metallic leaf
in preference to a lump of metal, because it offers to the action of the
gas but a small quantity of matter under a large surface. Filings, or
shavings, would answer the purpose nearly as well; but a lump of metal,
though the surface would oxydate with great rapidity, would not take
fire. Pure gold is not inflamed by oxy-muriatic acid gas, but it is
rapidly oxydated, and dissolved by it; indeed, this acid is the only one
that will dissolve gold.
EMILY.
This, I suppose, is what is commonly called _aqua regia_, which you know
is the only thing that will act upon gold.
MRS. B.
That is not exactly the case either; for aqua regia is composed of a
mixture of muriatic acid and nitric acid. --But, in fact, the result of
this mixture is the formation of oxy-muriatic acid, as the muriatic acid
oxygenates itself at the expence of the nitric; this mixture, therefore,
though it bears the name of _nitro-muriatic acid_, acts on gold merely
in virtue of the oxy-muriatic acid which it contains.
Sulphur, volatile oils, and many other substances, will burn in the same
manner in oxy-muriatic acid gas; but I have not prepared a sufficient
quantity of it, to show you the combustion of all these bodies.
CAROLINE.
There are several jars of the gas yet remaining.
MRS. B.
We must reserve these for future experiments. The oxy-muriatic acid does
not, like other acids, redden the blue vegetable colours; but it totally
destroys any colour, and turns all vegetables perfectly white. Let us
collect some vegetable substances to put into this glass, which is full
of gas.
EMILY.
Here is a sprig of myrtle--
CAROLINE.
And here some coloured paper--
MRS. B.
We shall also put in this piece of scarlet riband, and a rose--
EMILY.
Their colours begin to fade immediately! But how does the gas produce
this effect?
MRS. B.
The oxygen combines with the colouring matter of these substances, and
destroys it; that is to say, destroys the property which these colours
had of reflecting only one kind of rays, and renders them capable of
reflecting them all, which, you know, will make them appear white. Old
prints may be cleaned by this acid, for the paper will be whitened
without injury to the impression, as printer’s ink is made of materials
(oil and lamp black) which are not acted upon by acids.
This property of the oxy-muriatic acid has lately been employed in
manufactures in a variety of bleaching processes; but for these purposes
the gas must be dissolved in water, as the acid is thus rendered much
milder and less powerful in its effects; for, in a gaseous state, it
would destroy the texture, as well as the colour of the substance
submitted to its action.
CAROLINE.
Look at the things which we put into the gas; they have now entirely
lost their colour!
MRS. B.
The effect of the acid is almost completed; and, if we were to examine
the quantity that remains, we should find it to consist chiefly of
muriatic acid.
The oxy-muriatic acid has been used to purify the air in fever hospitals
and prisons, as it burns and destroys putrid effluvia of every kind. The
infection of the small-pox is likewise destroyed by this gas, and matter
that has been submitted to its influence will no longer generate that
disorder.
CAROLINE.
Indeed, I think the remedy must be nearly as bad as the disease; the
oxy-muriatic acid has such a dreadfully suffocating smell.
MRS. B.