have methodised the names of the elementary, as well as of the compound
bodies, though it could not have been done in the same manner. But the
names of the simple substances might have indicated their nature, or, at
least, some of their principal properties; and if, like the acids and
compound salts, all the simple bodies had a similar termination, they
would have been immediately known as such. So complete and regular a
nomenclature would, I think, have given a clearer and more comprehensive
view of chemistry than the present, which is a medley of the old and new
terms.
MRS. B.
But you are not aware of the difficulty of introducing into science an
entire set of new terms; it obliges all the teachers and professors to
go to school again, and if some of the old names, that are least
exceptionable, were not left as an introduction to the new ones, few
people would have had industry and perseverance enough to submit to the
study of a completely new language; and the inferior classes of artists,
who can only act from habit and routine, would, at least for a time,
have felt material inconvenience from a total change of their habitual
terms. From these considerations, Lavoisier and his colleagues, who
invented the new nomenclature, thought it most prudent to leave a few
links of the old chain, in order to connect it with the new one.
Besides, you may easily conceive the inconvenience which might arise
from giving a regular nomenclature to substances, the simple nature of
which is always uncertain; for the new names might, perhaps, have proved
to have been founded in error. And, indeed, cautious as the inventors of
the modern chemical language have been, it has already been found
necessary to modify it in many respects. In those few cases, however, in
which new terms have been adopted to designate simple bodies, these
names have been so contrived as to indicate one of the chief properties
of the body in question; this is the case with oxygen, which, as I
explained to you, signifies generator of acids; and hydrogen generator
of water. If all the elementary bodies had a similar termination, as you
propose, it would be necessary to change the name of any that might
hereafter be found of a compound nature, which would be very
inconvenient in this age of discovery.
But to return to the alkalies. --We shall now try to melt some of this
caustic potash in a little water, as a circumstance occurs during its
solution very worthy of observation. --Do you feel the heat that is
produced?
CAROLINE.
Yes, I do; but is not this directly contrary to our theory of latent
heat, according to which heat is disengaged when fluids become solid,
and cold produced when solids are melted?
MRS. B.
The latter is really the case in all solutions; and if the solution of
caustic alkalies seems to make an exception to the rule, it does not,
I believe, form any solid objection to the theory. The matter may be
explained thus: When water first comes in contact with the potash, it
produces an effect similar to the slaking of lime, that is, the water is
solidified in combining with the potash, and thus loses its latent heat;
this is the heat that you now feel, and which is, therefore, produced
not by the melting of the solid, but by the solidification of the fluid.
But when there is more water than the potash can absorb and solidify,
the latter then yields to the solvent power of the water; and if we do
not perceive the cold produced by its melting, it is because it is
counterbalanced by the heat previously disengaged.*
A very remarkable property of potash is the formation of glass by its
fusion with siliceous earth. You are not yet acquainted with this last
substance, further than its being in the list of simple bodies. It is
sufficient, for the present, that you should know that sand and flint
are chiefly composed of it; alone, it is infusible, but mixed with
potash, it melts when exposed to the heat of a furnace, combines with
the alkali, and runs into glass.
[Footnote *: This defence of the general theory, however
plausible, is liable to some obvious objections. The phenomenon
might perhaps be better accounted for by supposing that a solution
of alkali in water has less capacity for heat than either water or
alkali in their separate state.]
CAROLINE.
Who would ever have supposed that the same substance which converts
transparent oil into such an opake body as soap, should transform that
opake substance, sand, into transparent glass!
MRS. B.
The transparency, or opacity of bodies, does not, I conceive, depend so
much upon their intimate nature, as upon the arrangement of their
particles: we cannot have a more striking instance of this, than is
afforded by the different states of carbon, which, though it commonly
appears in the form of a black opake body, sometimes assumes the most
dazzling transparent form in nature, that of diamond, which, you
recollect, is carbon, and which, in all probability, derives its
beautiful transparency from the peculiar arrangement of its particles
during their crystallisation.
EMILY.
I never should have supposed that the formation of glass was so simple a
process as you describe it.
MRS. B.
It is by no means an easy operation to make perfect glass; for if the
sand, or flint, from which the siliceous earth is obtained, be mixed
with any metallic particles, or other substance, which cannot be
vitrified, the glass will be discoloured, or defaced, by opake specks.
CAROLINE.
That, I suppose, is the reason why objects so often appear irregular and
shapeless through a common glass-window.
MRS. B.
This species of imperfection proceeds, I believe, from another cause. It
is extremely difficult to prevent the lower part of the vessels, in
which the materials of glass are fused, from containing a more dense
vitreous matter than the upper, on account of the heavier ingredients
falling to the bottom. When this happens, it occasions the appearance of
veins or waves in the glass, from the difference of density in its
several parts, which produces an irregular refraction of the rays of
light that pass through it.
Another species of imperfection sometimes arises from the fusion not
being continued for a length of time sufficient to combine the two
ingredients completely, or from the due proportion of potash and silex
(which are as two to one) not being carefully observed; the glass, in
those cases, will be liable to alteration from the action of the air, of
salts, and especially of acids, which will effect its decomposition by
combining with the potash, and forming compound salts.
EMILY.
What an extremely useful substance potash is!
MRS. B.
Besides the great importance of potash in the manufactures of glass and
soap, it is of very considerable utility in many of the other arts, and
in its combinations with several acids, particularly the nitric, with
which it forms saltpetre.
CAROLINE.
Then saltpetre must be a _nitrat of potash_? But we are not yet
acquainted with the nitric acid?
MRS. B.
We shall therefore defer entering into the particulars of these
combinations till we come to a general review of the compound salts. In
order to avoid confusion, it will be better at present to confine
ourselves to the alkalies.
EMILY.
Cannot you show us the change of colour which you said the alkalies
produced on blue vegetable infusions?
MRS. B.
Yes; very easily. I shall dip a piece of white paper into this syrup of
violets, which, you see, is of a deep blue, and dyes the paper of the
same colour. --As soon as it is dry, we shall dip it into a solution of
potash, which, though itself colourless, will turn the paper green--
CAROLINE.
So it has, indeed! And do the other alkalies produce a similar effect?
MRS. B.
Exactly the same. --We may now proceed to SODA, which, however
important, will detain us but a very short time; as in all its general
properties it very strongly resembles potash; indeed, so great is their
similitude, that they have been long confounded, and they can now
scarcely be distinguished, except by the difference of the salts which
they form with acids.
The great source of this alkali is the sea, where, combined with a
peculiar acid, it forms the salt with which the waters of the ocean are
so strongly impregnated.
EMILY.
Is not that the common table salt?
MRS. B.
The very same; but again we must postpone entering into the particulars
of this interesting combination, till we treat of the neutral salts.
Soda may be obtained from common salt; but the easiest and most usual
method of procuring it is by the combustion of marine plants, an
operation perfectly analogous to that by which potash is obtained from
vegetables.
EMILY.
From what does soda derive its name?
MRS. B.
From a plant called by us _soda_, and by the Arabs _kali_, which affords
it in great abundance. Kali has, indeed, given its name to the alkalies
in general.
CAROLINE.
Does soda form glass and soap in the same manner as potash?
MRS. B.
Yes, it does; it is of equal importance in the arts, and is even
preferred to potash for some purposes; but you will not be able to
distinguish their properties till we examine the compound salts which
they form with acids; we must therefore leave soda for the present, and
proceed to AMMONIA, or the VOLATILE ALKALI.
EMILY.
I long to hear something of this alkali; is it not of the same nature as
hartshorn?
MRS. B.
Yes, it is, as you will see by-and-bye. This alkali is seldom found in
nature in its pure state; it is most commonly extracted from a compound
salt, called _sal ammoniac_, which was formerly imported from _Ammonia_,
a region of Libya, from which both these salts and the alkali derive
their names. The crystals contained in this bottle are specimens of this
salt, which consists of a combination of ammonia and muriatic acid.
CAROLINE.
Then it should be called _muriat of ammonia_; for though I am ignorant
what muriatic acid is, yet I know that its combination with ammonia
cannot but be so called; and I am surprised to see sal ammoniac
inscribed on the label.
MRS. B.
That is the name by which it has been so long known, that the modern
chemists have not yet succeeded in banishing it altogether; and it is
still sold under that name by druggists, though by scientific chemists
it is more properly called muriat of ammonia.
CAROLINE.
Both the popular and the common name should be inscribed on labels--this
would soon introduce the new nomenclature.
EMILY.
By what means can the ammonia be separated from the muriatic acid?
MRS. B.
By chemical attractions; but this operation is too complicated for you
to understand, till you are better acquainted with the agency of
affinities.
EMILY.
And when extracted from the salt, what kind of substance is ammonia?
MRS. B.
Its natural form, at the temperature of the atmosphere, when free from
combination, is that of gas; and in this state it is called _ammoniacal
gas_. But it mixes very readily with water, and can be thus obtained in
a liquid form.
CAROLINE.
You said that ammonia was more complicated in its composition than the
other alkalies; pray of what principles does it consist?
MRS. B.
It was discovered a few years since, by Berthollet, a celebrated French
chemist, that it consisted of about one part of hydrogen to four parts
of nitrogen. Having heated ammoniacal gas under a receiver, by causing
the electrical spark to pass repeatedly through it, he found that it
increased considerably in bulk, lost all its alkaline properties, and
was actually converted into hydrogen and nitrogen gases; and from the
latest and most accurate experiments, the proportions appear to be, one
volume of nitrogen gas to three of hydrogen gas.
CAROLINE.
Ammonia, therefore, has not, like the two other alkalies, a metallic
basis?
MRS. B.
It is believed it has, though it is extremely difficult to reconcile
that idea with what I have just stated of its chemical nature. But the
fact is, that although this supposed metallic basis of ammonia has never
been obtained distinct and separate, yet both Professor Berzelius, of
Stockholm, and Sir H. Davy, have succeeded in forming a combination of
mercury with the basis of ammonia, which has so much the appearance of
an amalgam, that it strongly corroborates the idea of ammonia having a
metallic basis.* But these theoretical points are full of difficulties
and doubts, and it would be useless to dwell any longer upon them.
Let us therefore return to the properties of volatile alkali. Ammoniacal
gas is considerably lighter than oxygen gas, and only about half the
weight of atmospherical air. It possesses most of the properties of the
fixed alkalies; but cannot be of so much use in the arts on account of
its volatile nature. It is, therefore, never employed in the manufacture
of glass, but it forms soap with oils equally as well as potash and
soda; it resembles them likewise in its strong attraction for water; for
which reason it can be collected in a receiver over mercury only.
[Footnote *: This amalgam is easily obtained, by placing a globule
of mercury upon a piece of muriat, or carbonat of ammonia, and
electrifying this globule by the Voltaic battery. The globule
instantly begins to expand to three or four times its former size,
and becomes much less fluid, though without losing its metallic
lustre, a change which is ascribed to the metallic basis of
ammonia uniting with the mercury. This is an extremely curious
experiment.]
CAROLINE.
I do not understand this?
MRS. B.
Do you recollect the method which we used to collect gases in a
glass-receiver over water?
CAROLINE.
Perfectly.
MRS. B.
Ammoniacal gas has so strong a tendency to unite with water, that,
instead of passing through that fluid, it would be instantaneously
absorbed by it. We can therefore neither use water for that purpose, nor
any other liquid of which water is a component part; so that, in order
to collect this gas, we are obliged to have recourse to mercury,
(a liquid which has no action upon it,) and a mercurial bath is used
instead of a water bath, such as we employed on former occasions. Water
impregnated with this gas is nothing more than the fluid which you
mentioned at the beginning of the conversation--hartshorn; it is the
ammoniacal gas escaping from the water which gives it so powerful a
smell.
EMILY.
But there is no appearance of effervescence in hartshorn.
MRS. B.
Because the particles of gas that rise from the water are too subtle and
minute for their effect to be visible.
Water diminishes in density, by being impregnated with ammoniacal gas;
and this augmentation of bulk increases its capacity for caloric.
EMILY.
In making hartshorn, then, or impregnating water with ammonia, heat must
be absorbed, and cold produced?
MRS. B.
That effect would take place if it was not counteracted by another
circumstance; the gas is liquefied by incorporating with the water, and
gives out its latent heat. The condensation of the gas more than
counterbalances the expansion of the water; therefore, upon the whole,
heat is produced. --But if you dissolve ammoniacal gas with ice or snow,
cold is produced. --Can you account for that?
EMILY.
The gas, in being condensed into a liquid, must give out heat; and, on
the other hand, the snow or ice, in being rarefied into a liquid, must
absorb heat; so that, between the opposite effects, I should have
supposed the original temperature would have been preserved.
MRS. B.
But you have forgotten to take into the account the rarefaction of the
water (or melted ice) by the impregnation of the gas; and this is the
cause of the cold which is ultimately produced.
CAROLINE.
Is the _sal volatile_ (the smell of which so strongly resembles
hartshorn) likewise a preparation of ammonia?
MRS. B.
It is carbonat of ammonia dissolved in water; and which, in its concrete
state, is commonly called salts of hartshorn. Ammonia is caustic, like
the fixed alkalies, as you may judge by the pungent effects of
hartshorn, which cannot be taken internally, nor applied to delicate
external parts, without being plentifully diluted with water. --Oil and
acids are very excellent antidotes for alkaline poisons; can you guess
why?
CAROLINE.
Perhaps, because the oil combines with the alkali, and forms soap, and
thus destroys its caustic properties; and the acid converts it into a
compound salt, which, I suppose, is not so pernicious as caustic alkali.
MRS. B.
Precisely so.
Ammoniacal gas, if it be mixed with atmospherical air, and a burning
taper repeatedly plunged into it, will burn with a large flame of a
peculiar yellow colour.
EMILY.
But pray tell me, can ammonia be procured from this Lybian salt only?
MRS. B.
So far from it, that it is contained in, and may be extracted from, all
animal substances whatever. Hydrogen and nitrogen are two of the chief
constituents of animal matter; it is therefore not surprising that they
should occasionally meet and combine in those proportions that compose
ammonia. But this alkali is more frequently generated by the spontaneous
decomposition of animal substances; the hydrogen and nitrogen gases that
arise from putrefied bodies combine, and form the volatile alkali.
Muriat of ammonia, instead of being exclusively brought from Lybia, as
it originally was, is now chiefly prepared in Europe, by chemical
processes. Ammonia, although principally extracted from this salt, can
also be produced by a great variety of other substances. The horns of
cattle, especially those of deer, yield it in abundance, and it is from
this circumstance that a solution of ammonia in water has been called
hartshorn. It may likewise be procured from wool, flesh, and bones; in a
word, any animal substance whatever yields it by decomposition.
We shall now lay aside the alkalies, however important the subject may
be, till we treat of their combination with acids. The next time we meet
we shall examine the earths.
CONVERSATION XV.
ON EARTHS.
MRS. B.
The EARTHS, which we are to-day to examine, are nine in number:
SILEX,
ALUMINE,
BARYTES,
LIME,
MAGNESIA,
STRONTITES,
YTTRIA,
GLUCINA,
ZIRCONIA.
The last three are of late discovery; their properties are but
imperfectly known; and, as they have not yet been applied to use, it
will be unnecessary to enter into any particulars respecting them; we
shall confine our remarks, therefore, to the first five. They are
composed, as you have already learnt, of a metallic basis combined with
oxygen; and, from this circumstance, are incombustible.
CAROLINE.
Yet I have seen turf burnt in the country, and it makes an excellent
fire; the earth becomes red hot, and produces a very great quantity of
heat.
MRS. B.
It is not the earth that burns, my dear, but the roots, grass, and other
remnants of vegetables that are intermixed with it. The caloric, which
is produced by the combustion of these substances, makes the earth red
hot, and this being a bad conductor of heat, retains its caloric a long
time; but were you to examine it when cooled, you would find that it had
not absorbed one particle of oxygen, nor suffered any alteration from
the fire. Earth is, however, from the circumstance just mentioned, an
excellent radiator of heat, and owes its utility, when mixed with fuel,
solely to that property. It is in this point of view that Count Rumford
has recommended balls of incombustible substances to be arranged in
fire-places, and mixed with the coals, by which means the caloric
disengaged by the combustion of the latter is more perfectly reflected
into the room, and an expense of fuel is saved.
EMILY.
I expected that the list of earths would be much more considerable. When
I think of the great variety of soils, I am astonished that there is not
a greater number of earths to form them.
MRS. B.
You might, indeed, almost confine that number to four; for barytes,
strontites, and the others of late discovery, act but so small a part in
this great theatre, that they cannot be reckoned as essential to the
general formation of the globe. And you must not confine your idea of
earths to the formation of soil; for rock, marble, chalk, slate, sand,
flint, and all kinds of stones, from the precious jewels to the
commonest pebbles; in a word, all the immense variety of mineral
products, may be referred to some of these earths, either in a simple
state, or combined the one with the other, or blended with other
ingredients.
CAROLINE.
Precious stones composed of earth! That seems very difficult to
conceive.
EMILY.
Is it more extraordinary than that the most precious of all jewels,
diamond, should be composed of carbon? But diamond forms an exception,
Mrs. B.; for, though a stone, it is not composed of earth.
MRS. B.
I did not specify the exception, as I knew you were so well acquainted
with it. Besides, I would call a diamond a mineral rather than a stone,
as the latter term always implies the presence of some earth.
CAROLINE.
I cannot conceive how such coarse materials can be converted into such
beautiful productions.
MRS. B.
We are very far from understanding all the secret resources of nature;
but I do not think the spontaneous formation of the crystals, which we
call precious stones, one of the most difficult phenomena to comprehend.
By the slow and regular work of ages, perhaps of hundreds of ages, these
earths may be gradually dissolved by water, and as gradually deposited
by their solvent in the undisturbed process of crystallisation. The
regular arrangement of their particles, during their reunion in a solid
mass, gives them that brilliancy, transparency, and beauty, for which
they are so much admired; and renders them in appearance so totally
different from their rude and primitive ingredients.
CAROLINE.
But how does it happen that they are spontaneously dissolved, and
afterwards crystallised?
MRS. B.
The scarcity of many kinds of crystals, as rubies, emeralds, topazes,
&c. shows that their formation is not an operation very easily carried
on in nature. But cannot you imagine that when water, holding in
solution some particles of earth, filters through the crevices of hills
or mountains, and at length dribbles into some cavern, each successive
drop may be slowly evaporated, leaving behind it the particle of earth
which it held in solution? You know that crystallisation is more regular
and perfect, in proportion as the evaporation of the solvent is slow and
uniform; nature, therefore, who knows no limit of time, has, in all
works of this kind, an infinite advantage over any artist who attempts
to imitate such productions.
EMILY.
I can now conceive that the arrangement of the particles of earth,
during crystallisation, may be such as to occasion transparency, by
admitting a free passage to the rays of light; but I cannot understand
why crystallised earths should assume such beautiful colours as most of
them do. Sapphire, for instance, is of a celestial blue; ruby, a deep
red; topaz, a brilliant yellow?
MRS. B.
Nothing is more simple than to suppose that the arrangement of their
particles is such, as to transmit some of the coloured rays of light,
and to reflect others, in which case the stone must appear of the colour
of the rays which it reflects. But besides, it frequently happens that
the colour of a stone is owing to a mixture of some metallic matter.
CAROLINE.
Pray, are the different kinds of precious stones each composed of one
individual earth, or are they formed of a combination of several earths?
MRS. B.
A great variety of materials enters into the composition of most of
them; not only several earths, but sometimes salts and metals. The
earths, however, in their simple state, frequently form very beautiful
crystals; and, indeed, it is in that state only that they can be
obtained perfectly pure.
EMILY.
Is not the Derbyshire spar produced by the crystallisation of earths, in
the way you have just explained? I have been in some of the
subterraneous caverns where it is found, which are similar to those you
have described.
MRS. B.
Yes; but this spar is a very imperfect specimen of crystallisation; it
consists of a variety of ingredients confusedly blended together, as you
may judge by its opacity, and by the various colours and appearances
which it exhibits.
But, in examining the earths in their most perfect and agreeable form,
we must not lose sight of that state in which they are commonly found,
and which, if less pleasing to the eye, is far more interesting by its
utility.