bodies, is nothing more than the power of decomposing air, and carrying
off its oxygen from the caloric with which it was combined, it is easily
understood that it cannot burn, unless in contact with air or oxygen
gas. Hence, when we set fire to a bottle full of this gas, it burns
gently, first at the neck of the bottle, and then in the inside of it,
in proportion as the external air gets in: This combustion is slow and
successive, and only takes place at the surface of contact between the
two gasses. It is quite different when the two gasses are mixed before
they are set on fire: If, for instance, after having introduced one part
of oxygen gas into a narrow mouthed bottle, we fill it up with two
parts of hydrogen gas, and bring a lighted taper, or other burning body,
to the mouth of the bottle, the combustion of the two gasses takes place
instantaneously with a violent explosion. This experiment ought only to
be made in a bottle of very strong green glass, holding not more than a
pint, and wrapped round with twine, otherwise the operator will be
exposed to great danger from the rupture of the bottle, of which the
fragments will be thrown about with great force.
If all that has been related above, concerning the decomposition of
water, be exactly conformable to truth;--if, as I have endeavoured to
prove, that substance be really composed of hydrogen, as its proper
constituent element, combined with oxygen, it ought to follow, that, by
reuniting these two elements together, we should recompose water; and
that this actually happens may be judged of by the following experiment.
_Experiment Fourth._
I took a large cristal baloon, A, Pl. iv. fig. 5. holding about 30
pints, having a large opening, to which was cemented the plate of copper
BC, pierced with four holes, in which four tubes terminate. The first
tube, H h, is intended to be adapted to an air pump, by which the
baloon is to be exhausted of its air. The second tube gg, communicates,
by its extremity MM, with a reservoir of oxygen gas, with which the
baloon is to be filled. The third tube d D d', communicates, by its
extremity d NN, with a reservoir of hydrogen gas. The extremity d' of
this tube terminates in a capillary opening, through which the hydrogen
gas contained in the reservoir is forced, with a moderate degree of
quickness, by the pressure of one or two inches of water. The fourth
tube contains a metallic wire GL, having a knob at its extremity L,
intended for giving an electrical spark from L to d', on purpose to set
fire to the hydrogen gas: This wire is moveable in the tube, that we may
be able to separate the knob L from the extremity d' of the tube D d'.
The three tubes d D d', gg, and H h, are all provided with stop-cocks.
That the hydrogen gas and oxygen gas may be as much as possible deprived
of water, they are made to pass, in their way to the baloon A, through
the tubes MM, NN, of about an inch diameter, and filled with salts,
which, from their deliquescent nature, greedily attract the moisture of
the air: Such are the acetite of potash, and the muriat or nitrat of
lime[18]. These salts must only be reduced to a coarse powder, lest
they run into lumps, and prevent the gasses from geting through their
interstices.
We must be provided before hand with a sufficient quantity of oxygen
gas, carefully purified from all admixture of carbonic acid, by long
contact with a solution of potash[19].
We must likewise have a double quantity of hydrogen gas, carefully
purified in the same manner by long contact with a solution of potash in
water. The best way of obtaining this gas free from mixture is, by
decomposing water with very pure soft iron, as directed in Exp. 3. of
this chapter.
Having adjusted every thing properly, as above directed, the tube H h is
adapted to an air-pump, and the baloon A is exhausted of its air. We
next admit the oxygen gas so as to fill the baloon, and then, by means
of pressure, as is before mentioned, force a small stream of hydrogen
gas through its tube D d', which we immediately set on fire by an
electric spark. By means of the above described apparatus, we can
continue the mutual combustion of these two gasses for a long time, as
we have the power of supplying them to the baloon from their reservoirs,
in proportion as they are consumed. I have in another place[20] given a
description of the apparatus used in this experiment, and have explained
the manner of ascertaining the quantities of the gasses consumed with
the most scrupulous exactitude.
In proportion to the advancement of the combustion, there is a
deposition of water upon the inner surface of the baloon or matrass A:
The water gradually increases in quantity, and, gathering into large
drops, runs down to the bottom of the vessel. It is easy to ascertain
the quantity of water collected, by weighing the baloon both before and
after the experiment. Thus we have a twofold verification of our
experiment, by ascertaining both the quantities of the gasses employed,
and of the water formed by their combustion: These two quantities must
be equal to each other. By an operation of this kind, Mr Meusnier and I
ascertained that it required 85 parts, by weight, of oxygen, united to
15 parts of hydrogen, to compose 100 parts of water. This experiment,
which has not hitherto been published, was made in presence of a
numerous committee from the Royal Academy. We exerted the most
scrupulous attention to its accuracy; and have reason to believe that
the above propositions cannot vary a two hundredth part from absolute
truth.
From these experiments, both analytical and synthetic, we may now affirm
that we have ascertained, with as much certainty as is possible in
physical or chemical subjects, that water is not a simple elementary
substance, but is composed of two elements, oxygen and hydrogen; which
elements, when existing separately, have so strong affinity for caloric,
as only to subsist under the form of gas in the common temperature and
pressure of our atmosphere.
This decomposition and recomposition of water is perpetually operating
before our eyes, in the temperature of the atmosphere, by means of
compound elective attraction. We shall presently see that the phenomena
attendant upon vinous fermentation, putrefaction, and even vegetation,
are produced, at least in a certain degree, by decomposition of water.
It is very extraordinary that this fact should have hitherto been
overlooked by natural philosophers and chemists: Indeed, it strongly
proves, that, in chemistry, as in moral philosophy, it is extremely
difficult to overcome prejudices imbibed in early education, and to
search for truth in any other road than the one we have been accustomed
to follow.
I shall finish this chapter by an experiment much less demonstrative
than those already related, but which has appeared to make more
impression than any other upon the minds of many people. When 16 ounces
of alkohol are burnt in an apparatus[21] properly adapted for collecting
all the water disengaged during the combustion, we obtain from 17 to 18
ounces of water. As no substance can furnish a product larger than its
original bulk, it follows, that something else has united with the
alkohol during its combustion; and I have already shown that this must
be oxygen, or the base of air. Thus alkohol contains hydrogen, which is
one of the elements of water; and the atmospheric air contains oxygen,
which is the other element necessary to the composition of water. This
experiment is a new proof that water is a compound substance.
FOOTNOTES:
[16] In the latter part of this work will be found a particular account
of the processes necessary for separating the different kinds of gasses,
and for determining their quantities.--A.
[17] This expression Hydrogen has been very severely criticised by some,
who pretend that it signifies engendered by water, and not that which
engenders water. The experiments related in this chapter prove, that,
when water is decomposed, hydrogen is produced, and that, when hydrogen
is combined with oxygen, water is produced: So that we may say, with
equal truth, that water is produced from hydrogen, or hydrogen is
produced from water.--A.
[18] See the nature of these salts in the second part of this book.--A.
[19] By potash is here meant, pure or caustic alkali, deprived of
carbonic acid by means of quick-lime: In general, we may observe here,
that all the alkalies and earths must invariably be considered as in
their pure or caustic state, unless otherwise expressed.--E. The method
of obtaining this pure alkali of potash will be given in the sequel.--A.
[20] See the third part of this work.--A.
[21] See an account of this apparatus in the third part of this
work.--A.
CHAP. IX.
_Of the quantities of Caloric disengaged from different species of
Combustion._
We have already mentioned, that, when any body is burnt in the center of
a hollow sphere of ice and supplied with air at the temperature of zero
(32 deg.), the quantity of ice melted from the inside of the sphere
becomes a measure of the relative quantities of caloric disengaged. Mr
de la Place and I gave a description of the apparatus employed for this
kind of experiment in the Memoirs of the Academy for 1780, p. 355; and a
description and plate of the same apparatus will be found in the third
part of this work. With this apparatus, phosphorus, charcoal, and
hydrogen gas, gave the following results:
One pound of phosphorus melted 100 libs. of ice.
One pound of charcoal melted 96 libs. 8 oz.
One pound of hydrogen gas melted 295 libs. 9 oz. 3-1/2 gros.
As a concrete acid is formed by the combustion of phosphorus, it is
probable that very little caloric remains in the acid, and,
consequently, that the above experiment gives us very nearly the whole
quantity of caloric contained in the oxygen gas. Even if we suppose the
phosphoric acid to contain a good deal of caloric, yet, as the
phosphorus must have contained nearly an equal quantity before
combustion, the error must be very small, as it will only consist of the
difference between what was contained in the phosphorus before, and in
the phosphoric acid after combustion.
I have already shown in Chap. V. that one pound of phosphorus absorbs
one pound eight ounces of oxygen during combustion; and since, by the
same operation, 100 lib. of ice are melted, it follows, that the
quantity of caloric contained in one pound of oxygen gas is capable of
melting 66 libs. 10 oz. 5 gros 24 grs. of ice.
One pound of charcoal during combustion melts only 96 libs. 8 oz. of
ice, whilst it absorbs 2 libs. 9 oz. 1 gros 10 grs. of oxygen.
By the experiment with phosphorus, this quantity of oxygen gas ought to
disengage a quantity of caloric sufficient to melt 171 libs. 6 oz. 5
gros of ice; consequently, during this experiment, a quantity of
caloric, sufficient to melt 74 libs. 14 oz. 5 gros of ice
disappears. Carbonic acid is not, like phosphoric acid, in a concrete
state after combustion but in the state of gas, and requires to be
united with caloric to enable it to subsist in that state; the quantity
of caloric missing in the last experiment is evidently employed for that
purpose. When we divide that quantity by the weight of carbonic acid,
formed by the combustion of one pound of charcoal, we find that the
quantity of caloric necessary for changing one pound of carbonic acid
from the concrete to the gasseous state, would be capable of melting 20
libs. 15 oz. 5 gros of ice.
We may make a similar calculation with the combustion of hydrogen gas
and the consequent formation of water. During the combustion of one
pound of hydrogen gas, 5 libs. 10 oz. 5 gros 24 grs. of oxygen
gas are absorbed, and 295 libs. 9 oz. 3-1/2 gros of ice are
melted. But 5 libs. 10 oz. 5 gros 24 grs. of oxygen gas, in
changing from the aeriform to the solid state, loses, according to the
experiment with phosphorus, enough of caloric to have melted 377 libs.
12 oz. 3 gros of ice. There is only disengaged, from the same
quantity of oxygen, during its combustion with hydrogen gas, as much
caloric as melts 295 libs. 2 oz. 3-1/2 gros; wherefore there
remains in the water at Zero (32 deg.), formed, during this experiment,
as much caloric as would melt 82 libs. 9 oz. 7-1/2 gros of ice.
Hence, as 6 libs. 10 oz. 5 gros 24 grs. of water are formed from
the combustion of one pound of hydrogen gas with 5 libs. 10 oz. 5
gros 24 grs. of oxygen, it follows that, in each pound of water, at
the temperature of Zero, (32 deg.), there exists as much caloric as
would melt 12 libs. 5 oz. 2 gros 48 grs. of ice, without taking into
account the quantity originally contained in the hydrogen gas, which we
have been obliged to omit, for want of data to calculate its quantity.
From this it appears that water, even in the state of ice, contains a
considerable quantity of caloric, and that oxygen, in entering into that
combination, retains likewise a good proportion.
From these experiments, we may assume the following results as
sufficiently established.
_Combustion of Phosphorus._
From the combustion of phosphorus, as related in the foregoing
experiments, it appears, that one pound of phosphorus requires 1 lib.
8 oz. of oxygen gas for its combustion, and that 2 libs. 8 oz. of
concrete phosphoric acid are produced.
The quantity of caloric disengaged by the
combustion of one pound of phosphorus, expressed
by the number of pounds of ice melted
during that operation, is 100.00000.
The quantity disengaged from each pound of
oxygen, during the combustion of phosphorus,
expressed in the same manner, is 66.66667.
The quantity disengaged during the formation
of one pound of phosphoric acid, 40.00000.
The quantity remaining in each pound of phosphoric
acid, 0.00000(A).
[Note A: We here suppose the phosphoric acid not to contain any caloric,
which is not strictly true; but, as I have before observed, the quantity
it really contains is probably very small, and we have not given it a
value, for want of a sufficient data to go upon.--A.]
_Combustion of Charcoal._
In the combustion of one pound of charcoal, 2 libs. 9 oz. 1 gros
10 grs. of oxygen gas are absorbed, and 3 libs. 9 oz. 1 gros 10
grs. of carbonic acid gas are formed.
Caloric, disengaged daring the combustion
of one pound of charcoal, 96.50000(A).
Caloric disengaged during the combustion of
charcoal, from each pound of oxygen gas
absorbed, 37.52823.
Caloric disengaged during the formation of
one pound of carbonic acid gas, 27.02024.
Caloric retained by each pound of oxygen
after the combustion, 29.13844.
Caloric necessary for supporting one pound
of carbonic acid in the state of gas, 20.97960.
[Note A: All these relative quantities of caloric are expressed by the
number of pounds of ice, and decimal parts, melted during the several
operations.--E.]
_Combustion of Hydrogen Gas._
In the combustion of one pound of hydrogen gas, 5 libs. 10 oz. 5
gros 24 grs. of oxygen gas are absorbed, and 6 libs. 10 oz. 5
gros 24 grs. of water are formed.
Caloric from each lib. of hydrogen gas, 295.58950.
Caloric from each lib. of oxygen gas, 52.16280.
Caloric disengaged during the formation of each pound of water, 44.33840.
Caloric retained by each lib. of oxygen after
combustion with hydrogen, 14.50386.
Caloric retained by each lib. of water at
the temperature of Zero (32 deg.), 12.32823.
_Of the Formation of Nitric Acid._
When we combine nitrous gas with oxygen gas, so as to form nitric or
nitrous acid a degree of heat is produced, which is much less
considerable than what is evolved during the other combinations of
oxygen; whence it follows that oxygen, when it becomes fixed in nitric
acid, retains a great part of the heat which it possessed in the state
of gas. It is certainly possible to determine the quantity of caloric
which is disengaged during the combination of these two gasses, and
consequently to determine what quantity remains after the combination
takes place. The first of these quantities might be ascertained, by
making the combination of the two gasses in an apparatus surrounded by
ice; but, as the quantity of caloric disengaged is very inconsiderable,
it would be necessary to operate upon a large quantity of the two gasses
in a very troublesome and complicated apparatus. By this consideration,
Mr de la Place and I have hitherto been prevented from making the
attempt. In the mean time, the place of such an experiment may be
supplied by calculations, the results of which cannot be very far from
truth.
Mr de la Place and I deflagrated a convenient quantity of nitre and
charcoal in an ice apparatus, and found that twelve pounds of ice were
melted by the deflagration of one pound of nitre. We shall see, in the
sequel, that one pound of nitre is composed, as under, of
Potash 7 oz. 6 gros 51.84 grs. = 4515.84 grs.
Dry acid 8 1 21.16 = 4700.16.
The above quantity of dry acid is composed of
Oxygen 6 oz. 3 gros 66.34 grs. = 3738.34 grs.
Azote 1 5 25.82 = 961.82.
By this we find that, during the above deflagration, 2 gros 1-1/3
gr. of charcoal have suffered combustion, alongst with 3738.34 grs.
or 6 oz. 3 gros 66.34 grs. of oxygen. Hence, since 12 libs. of
ice were melted during the combustion, it follows, that one pound of
oxygen burnt in the same manner would have melted 29.58320 libs. of
ice. To which the quantity of caloric, retained by a pound of oxygen
after combining with charcoal to form carbonic acid gas, being added,
which was already ascertained to be capable of melting 29.13844 libs.
of ice, we have for the total quantity of caloric remaining in a pound
of oxygen, when combined with nitrous gas in the nitric acid 58.72164;
which is the number of pounds of ice the caloric remaining in the oxygen
in that state is capable of melting.
We have before seen that, in the state of oxygen gas, it contained at
least 66.66667; wherefore it follows that, in combining with azote to
form nitric acid, it only loses 7.94502. Farther experiments upon this
subject are necessary to ascertain how far the results of this
calculation may agree with direct fact. This enormous quantity of
caloric retained by oxygen in its combination into nitric acid, explains
the cause of the great disengagement of caloric during the
deflagrations of nitre; or, more strictly speaking, upon all occasions
of the decomposition of nitric acid.
_Of the Combustion of Wax._
Having examined several cases of simple combustion, I mean now to give a
few examples of a more complex nature. One pound of wax-taper being
allowed to burn slowly in an ice apparatus, melted 133 libs. 2 oz.
5-1/3 gros of ice. According to my experiments in the Memoirs of the
Academy for 1784, p. 606, one pound of wax-taper consists of 13 oz. 1
gros 23 grs. of charcoal, and 2 oz. 6 gros 49 grs. of
hydrogen.
By the foregoing experiments, the above
quantity of charcoal ought to melt 79.39390 libs. of ice;
and the hydrogen should melt 52.37605
---------
In all 131.76995 libs.
Thus, we see the quantity of caloric disengaged from a burning taper, is
pretty exactly conformable to what was obtained by burning separately a
quantity of charcoal and hydrogen equal to what enters into its
composition. These experiments with the taper were several times
repeated, so that I have reason to believe them accurate.
_Combustion of Olive Oil._
We included a burning lamp, containing a determinate quantity of
olive-oil, in the ordinary apparatus, and, when the experiment was
finished, we ascertained exactly the quantities of oil consumed, and of
ice melted; the result was, that, during the combustion of one pound of
olive-oil, 148 libs. 14 oz. 1 gros of ice were melted. By my
experiments in the Memoirs of the Academy for 1784, and of which the
following Chapter contains an abstract, it appears that one pound of
olive-oil consists of 12 oz. 5 gros 5 grs. of charcoal, and 3
oz. 2 gros 67 grs. of hydrogen. By the foregoing experiments, that
quantity of charcoal should melt 76.18723 libs. of ice, and the
quantity of hydrogen in a pound of the oil should melt 62.15053 libs.
The sum of these two gives 138.33776 libs. of ice, which the two
constituent elements of the oil would have melted, had they separately
suffered combustion, whereas the oil really melted 148.88330 libs.
which gives an excess of 10.54554 in the result of the experiment above
the calculated result, from data furnished by former experiments.
This difference, which is by no means very considerable, may arise from
errors which are unavoidable in experiments of this nature, or it may be
owing to the composition of oil not being as yet exactly ascertained. It
proves, however, that there is a great agreement between the results of
our experiments, respecting the combination of caloric, and those which
regard its disengagement.
The following desiderata still remain to be determined, viz. What
quantity of caloric is retained by oxygen, after combining with metals,
so as to convert them into oxyds; What quantity is contained by
hydrogen, in its different states of existence; and to ascertain, with
more precision than is hitherto attained, how much caloric is disengaged
during the formation of water, as there still remain considerable doubts
with respect to our present determination of this point, which can only
be removed by farther experiments. We are at present occupied with this
inquiry; and, when once these several points are well ascertained, which
we hope they will soon be, we shall probably be under the necessity of
making considerable corrections upon most of the results of the
experiments and calculations in this Chapter. I did not, however,
consider this as a sufficient reason for withholding so much as is
already known from such as may be inclined to labour upon the same
subject. It is difficult, in our endeavours to discover the principles
of a new science, to avoid beginning by guess-work; and it is rarely
possible to arrive at perfection from the first setting out.
CHAP. X.
_Of the Combination of Combustible Substances with each other._
As combustible substances in general have a great affinity for oxygen,
they ought likewise to attract, or tend to combine with each other;
_quae sunt eadem uni tertio, sunt eadem inter se_; and the axiom is
found to be true. Almost all the metals, for instance, are capable of
uniting with each other, and forming what are called _alloys_[22], in
common language. Most of these, like all combinations, are susceptible
of several degrees of saturation; the greater number of these alloys are
more brittle than the pure metals of which they are composed, especially
when the metals alloyed together are considerably different in their
degrees of fusibility. To this difference in fusibility, part of the
phenomena attendant upon _alloyage_ are owing, particularly the property
of iron, called by workmen _hotshort_. This kind of iron must be
considered as an alloy, or mixture of pure iron, which is almost
infusible, with a small portion of some other metal which fuses in a
much lower degree of heat. So long as this alloy remains cold, and both
metals are in the solid state, the mixture is malleable; but, if heated
to a sufficient degree to liquify the more fusible metal, the particles
of the liquid metal, which are interposed between the particles of the
metal remaining solid, must destroy their continuity, and occasion the
alloy to become brittle. The alloys of mercury, with the other metals,
have usually been called _amalgams_, and we see no inconvenience from
continuing the use of that term.
Sulphur, phosphorus, and charcoal, readily unite with metals.
Combinations of sulphur with metals are usually named _pyrites_. Their
combinations with phosphorus and charcoal are either not yet named, or
have received new names only of late; so that we have not scrupled to
change them according to our principles. The combinations of metal and
sulphur we call _sulphurets_, those with phosphorus _phosphurets_, and
those formed with charcoal _carburets_. These denominations are extended
to all the combinations into which the above three substances enter,
without being previously oxygenated. Thus, the combination of sulphur
with potash, or fixed vegetable alkali, is called _sulphuret of potash_;
that which it forms with ammoniac, or volatile alkali, is termed
_sulphuret of ammoniac_.
Hydrogen is likewise capable of combining with many combustible
substances. In the state of gas, it dissolves charcoal, sulphur,
phosphorus, and several metals; we distinguish these combinations by the
terms, _carbonated hydrogen gas_, _sulphurated hydrogen gas_, and
_phosphorated hydrogen gas_. The sulphurated hydrogen gas was called
_hepatic air_ by former chemists, or _foetid air from sulphur_, by Mr
Scheele. The virtues of several mineral waters, and the foetid smell of
animal excrements, chiefly arise from the presence of this gas. The
phosphorated hydrogen gas is remarkable for the property, discovered by
Mr Gengembre, of taking fire spontaneously upon getting into contact
with atmospheric air, or, what is better, with oxygen gas. This gas has
a strong flavour, resembling that of putrid fish; and it is very
probable that the phosphorescent quality of fish, in the state of
putrefaction, arises from the escape of this species of gas. When
hydrogen and charcoal are combined together, without the intervention of
caloric, to bring the hydrogen into the state of gas, they form oil,
which is either fixed or volatile, according to the proportions of
hydrogen and charcoal in its composition. The chief difference between
fixed or fat oils drawn from vegetables by expression, and volatile or
essential oils, is, that the former contains an excess of charcoal,
which is separated when the oils are heated above the degree of boiling
water; whereas the volatile oils, containing a just proportion of these
two constituent ingredients, are not liable to be decomposed by that
heat, but, uniting with caloric into the gasseous state, pass over in
distillation unchanged.
In the Memoirs of the Academy for 1784, p. 593. I gave an account of my
experiments upon the composition of oil and alkohol, by the union of
hydrogen with charcoal, and of their combination with oxygen. By these
experiments, it appears that fixed oils combine with oxygen during
combustion, and are thereby converted into water and carbonic acid. By
means of calculation applied to the products of these experiments, we
find that fixed oil is composed of 21 parts, by weight, of hydrogen
combined with 79 parts of charcoal. Perhaps the solid substances of an
oily nature, such as wax, contain a proportion of oxygen, to which they
owe their state of solidity. I am at present engaged in a series of
experiments, which I hope will throw great light upon this subject.
It is worthy of being examined, whether hydrogen in its concrete state,
uncombined with caloric, be susceptible of combination with sulphur,
phosphorus, and the metals. There is nothing that we know of, which, _a
priori_, should render these combinations impossible; for combustible
bodies being in general susceptible of combination with each other,
there is no evident reason for hydrogen being an exception to the rule:
However, no direct experiment as yet establishes either the possibility
or impossibility of this union. Iron and zinc are the most likely, of
all the metals, for entering into combination with hydrogen; but, as
these have the property of decomposing water, and as it is very
difficult to get entirely free from moisture in chemical experiments, it
is hardly possible to determine whether the small portions of hydrogen
gas, obtained in certain experiments with these metals, were previously
combined with the metal in the state of solid hydrogen, or if they were
produced by the decomposition of a minute quantity of water. The more
care we take to prevent the presence of water in these experiments, the
less is the quantity of hydrogen gas procured; and, when very accurate
precautions are employed, even that quantity becomes hardly sensible.
However this inquiry may turn out respecting the power of combustible
bodies, as sulphur, phosphorus, and metals, to absorb hydrogen, we are
certain that they only absorb a very small portion; and that this
combination, instead of being essential to their constitution, can only
be considered as a foreign substance, which contaminates their purity.
It is the province of the advocates[23] for this system to prove, by
decisive experiments, the real existence of this combined hydrogen,
which they have hitherto only done by conjectures founded upon
suppositions.
FOOTNOTES:
[22] This term _alloy_, which we have from the language of the arts,
serves exceedingly well for distinguishing all the combinations or
intimate unions of metals with each other, and is adopted in our new
nomenclature for that purpose.--A.
[23] By these are meant the supporters of the phlogistic theory, who at
present consider hydrogen, or the base of inflammable air, as the
phlogiston of the celebrated Stahl.--E.
CHAP. XI.
_Observations upon Oxyds and Acids with several Bases--and upon the
Composition of Animal and Vegetable Substances._
We have, in Chap. V. and VIII. examined the products resulting from the
combustion of the four simple combustible substances, sulphur,
phosphorus, charcoal, and hydrogen: We have shown, in Chap. X that the
simple combustible substances are capable of combining with each other
into compound combustible substances, and have observed that oils in
general, and particularly the fixed vegetable oils, belong to this
class, being composed of hydrogen and charcoal. It remains, in this
chapter, to treat of the oxygenation of these compound combustible
substances, and to show that there exist acids and oxyds having double
and triple bases. Nature furnishes us with numerous examples of this
kind of combinations, by means of which, chiefly, she is enabled to
produce a vast variety of compounds from a very limited number of
elements, or simple substances.
It was long ago well known, that, when muriatic and nitric acids were
mixed together, a compound acid was formed, having properties quite
distinct from those of either of the acids taken separately. This acid
was called _aqua regia_, from its most celebrated property of dissolving
gold, called _king of metals_ by the alchymists. Mr Berthollet has
distinctly proved that the peculiar properties of this acid arise from
the combined action of its two acidifiable bases; and for this reason we
have judged it necessary to distinguish it by an appropriate name: That
of _nitro-muriatic_ acid appears extremely applicable, from its
expressing the nature of the two substances which enter into its
composition.
This phenomenon of a double base in one acid, which had formerly been
observed only in the nitro-muriatic acid, occurs continually in the
vegetable kingdom, in which a simple acid, or one possessed of a single
acidifiable base, is very rarely found. Almost all the acids procurable
from this kingdom have bases composed of charcoal and hydrogen, or of
charcoal, hydrogen, and phosphorus, combined with more or less oxygen.
All these bases, whether double or triple, are likewise formed into
oxyds, having less oxygen than is necessary to give them the properties
of acids. The acids and oxyds from the animal kingdom are still more
compound, as their bases generally consist of a combination of
charcoal, phosphorus, hydrogen, and azote.
As it is but of late that I have acquired any clear and distinct notions
of these substances, I shall not, in this place, enlarge much upon the
subject, which I mean to treat of very fully in some memoirs I am
preparing to lay before the Academy. Most of my experiments are already
performed; but, to be able to give exact reports of the resulting
quantities, it is necessary that they be carefully repeated, and
increased in number: Wherefore, I shall only give a short enumeration of
the vegetable and animal acids and oxyds, and terminate this article by
a few reflections upon the composition of vegetable and animal bodies.
Sugar, mucus, under which term we include the different kinds of gums,
and starch, are vegetable oxyds, having hydrogen and charcoal combined,
in different proportions, as their radicals or bases, and united with
oxygen, so as to bring them to the state of oxyds. From the state of
oxyds they are capable of being changed into acids by the addition of a
fresh quantity of oxygen; and, according to the degrees of oxygenation,
and the proportion of hydrogen and charcoal in their bases, they form
the several kinds of vegetable acids.
It would be easy to apply the principles of our nomenclature to give
names to these vegetable acids and oxyds, by using the names of the two
substances which compose their bases: They would thus become
hydro-carbonous acids and oxyds: In this method we might indicate which
of their elements existed in excess, without circumlocution, after the
manner used by Mr Rouelle for naming vegetable extracts: He calls these
extracto-resinous when the extractive matter prevails in their
composition, and resino-extractive when they contain a larger proportion
of resinous matter. Upon that plan, and by varying the terminations
according to the formerly established rules of our nomenclature, we have
the following denominations: Hydro-carbonous, hydro-carbonic;
carbono-hydrous, and carbono-hydric oxyds. And for the acids:
Hydro-carbonous, hydro carbonic, oxygenated hydro-carbonic;
carbono-hydrous, carbono-hydric, and oxygenated carbono-hydric. It is
probable that the above terms would suffice for indicating all the
varieties in nature, and that, in proportion as the vegetable acids
become well understood, they will naturally arrange themselves under
these denominations. But, though we know the elements of which these are
composed, we are as yet ignorant of the proportions of these
ingredients, and are still far from being able to class them in the
above methodical manner; wherefore, we have determined to retain the
ancient names provisionally. I am somewhat farther advanced in this
inquiry than at the time of publishing our conjunct essay upon chemical
nomenclature; yet it would be improper to draw decided consequences from
experiments not yet sufficiently precise: Though I acknowledge that this
part of chemistry still remains in some degree obscure, I must express
my expectations of its being very soon elucidated.
I am still more forcibly necessitated to follow the same plan in naming
the acids, which have three or four elements combined in their bases; of
these we have a considerable number from the animal kingdom, and some
even from vegetable substances. Azote, for instance, joined to hydrogen
and charcoal, form the base or radical of the Prussic acid; we have
reason to believe that the same happens with the base of the Gallic
acid; and almost all the animal acids have their bases composed of
azote, phosphorus, hydrogen, and charcoal. Were we to endeavour to
express at once all these four component parts of the bases, our
nomenclature would undoubtedly be methodical; it would have the property
of being clear and determinate; but this assemblage of Greek and Latin
substantives and adjectives, which are not yet universally admitted by
chemists, would have the appearance of a barbarous language, difficult
both to pronounce and to be remembered. Besides, this part of chemistry
being still far from that accuracy it must arrive to, the perfection of
the science ought certainly to precede that of its language; and we must
still, for some time, retain the old names for the animal oxyds and
acids. We have only ventured to make a few slight modifications of these
names, by changing the termination into _ous_, when we have reason to
suppose the base to be in excess, and into _ic_, when we suspect the
oxygen predominates.
The following are all the vegetable acids hitherto known:
1. Acetous acid.
2. Acetic acid.
3. Oxalic acid.
4. Tartarous acid.
5. Pyro-tartarous acid.
6. Citric acid.
7. Malic acid.
8. Pyro-mucous acid.
9. Pyro-lignous acid.
10. Gallic acid.
11. Benzoic acid.
12. Camphoric acid.
13. Succinic acid.
Though all these acids, as has been already said, are chiefly, and
almost entirely, composed of hydrogen, charcoal, and oxygen, yet,
properly speaking, they contain neither water carbonic acid nor oil, but
only the elements necessary for forming these substances. The power of
affinity reciprocally exerted by the hydrogen, charcoal, and oxygen, in
these acids, is in a state of equilibrium only capable of existing in
the ordinary temperature of the atmosphere; for, when they are heated
but a very little above the temperature of boiling water, this
equilibrium is destroyed, part of the oxygen and hydrogen unite, and
form water; part of the charcoal and hydrogen combine into oil; part of
the charcoal and oxygen unite to form carbonic acid; and, lastly, there
generally remains a small portion of charcoal, which, being in excess
with respect to the other ingredients, is left free. I mean to explain
this subject somewhat farther in the succeeding chapter.
The oxyds of the animal kingdom are hitherto less known than those from
the vegetable kingdom, and their number is as yet not at all determined.
The red part of the blood, lymph, and most of the secretions, are true
oxyds, under which point of view it is very important to consider them.
We are only acquainted with six animal acids, several of which, it is
probable, approach very near each other in their nature, or, at least,
differ only in a scarcely sensible degree. I do not include the
phosphoric acid amongst these, because it is found in all the kingdoms
of nature. They are,
1. Lactic acid.
2. Saccholactic acid.
3. Bombic acid.
4. Formic acid.
5. Sebacic acid.
6. Prussic acid.
The connection between the constituent elements of the animal oxyds and
acids is not more permanent than in those from the vegetable kingdom, as
a small increase of temperature is sufficient to overturn it. I hope to
render this subject more distinct than has been done hitherto in the
following chapter.
CHAP. XII.
_Of the Decomposition of Vegetable and Animal Substances by the Action
of Fire._
Before we can thoroughly comprehend what takes place during the
decomposition of vegetable substances by fire, we must take into
consideration the nature of the elements which enter into their
composition, and the different affinities which the particles of these
elements exert upon each other, and the affinity which caloric possesses
with them. The true constituent elements of vegetables are hydrogen,
oxygen, and charcoal: These are common to all vegetables, and no
vegetable can exist without them: Such other substances as exist in
particular vegetables are only essential to the composition of those in
which they are found, and do not belong to vegetables in general.
Of these elements, hydrogen and oxygen have a strong tendency to unite
with caloric, and be converted into gas, whilst charcoal is a fixed
element, having but little affinity with caloric. On the other hand,
oxygen, which, in the usual temperature, tends nearly equally to unite
with hydrogen and with charcoal, has a much stronger affinity with
charcoal when at the red heat[24], and then unites with it to form
carbonic acid.
Although we are far from being able to appreciate all these powers of
affinity, or to express their proportional energy by numbers, we are
certain, that, however variable they may be when considered in relation
to the quantity of caloric with which they are combined, they are all
nearly in equilibrium in the usual temperature of the atmosphere; hence
vegetables neither contain oil[25], water, nor carbonic acid, tho' they
contain all the elements of these substances. The hydrogen is neither
combined with the oxygen nor with the charcoal, and reciprocally; the
particles of these three substances form a triple combination, which
remains in equilibrium whilst undisturbed by caloric but a very slight
increase of temperature is sufficient to overturn this structure of
combination.
If the increased temperature to which the vegetable is exposed does not
exceed the heat of boiling water, one part of the hydrogen combines with
the oxygen, and forms water, the rest of the hydrogen combines with a
part of the charcoal, and forms volatile oil, whilst the remainder of
the charcoal, being set free from its combination with the other
elements, remains fixed in the bottom of the distilling vessel.
When, on the contrary, we employ a red heat, no water is formed, or, at
least, any that may have been produced by the first application of the
heat is decomposed, the oxygen having a greater affinity with the
charcoal at this degree of heat, combines with it to form carbonic acid,
and the hydrogen being left free from combination with the other
elements, unites with caloric, and escapes in the state of hydrogen gas.
In this high temperature, either no oil is formed, or, if any was
produced during the lower temperature at the beginning of the
experiment, it is decomposed by the action of the red heat. Thus the
decomposition of vegetable matter, under a high temperature, is produced
by the action of double and triple affinities; while the charcoal
attracts the oxygen, on purpose to form carbonic acid, the caloric
attracts the hydrogen, and converts it into hydrogen gas.
The distillation of every species of vegetable substance confirms the
truth of this theory, if we can give that name to a simple relation of
facts. When sugar is submitted to distillation, so long as we only
employ a heat but a little below that of boiling water, it only loses
its water of cristallization, it still remains sugar, and retains all
its properties; but, immediately upon raising the heat only a little
above that degree, it becomes blackened, a part of the charcoal
separates from the combination, water slightly acidulated passes over
accompanied by a little oil, and the charcoal which remains in the
retort is nearly a third part of the original weight of the sugar.
The operation of affinities which take place during the decomposition,
by fire, of vegetables which contain azote, such as the cruciferous
plants, and of those containing phosphorus, is more complicated; but, as
these substances only enter into the composition of vegetables in very
small quantities, they only, apparently, produce slight changes upon the
products of distillation; the phosphorus seems to combine with the
charcoal, and, acquiring fixity from that union, remains behind in the
retort, while the azote, combining with a part of the hydrogen, forms
ammoniac, or volatile alkali.
Animal substances, being composed nearly of the same elements with
cruciferous plants, give the same products in distillation, with this
difference, that, as they contain a greater quantity of hydrogen and
azote, they produce more oil and more ammoniac. I shall only produce one
fact as a proof of the exactness with which this theory explains all the
phenomena which occur during the distillation of animal substances,
which is the rectification and total decomposition of volatile animal
oil, commonly known by the name of Dippel's oil. When these oils are
procured by a first distillation in a naked fire they are brown, from
containing a little charcoal almost in a free state; but they become
quite colourless by rectification. Even in this state the charcoal in
their composition has so slight a connection with the other elements as
to separate by mere exposure to the air. If we put a quantity of this
animal oil, well rectified, and consequently clear, limpid, and
transparent, into a bell-glass filled with oxygen gas over mercury, in a
short time the gas is much diminished, being absorbed by the oil, the
oxygen combining with the hydrogen of the oil forms water, which sinks
to the bottom, at the same time the charcoal which was combined with the
hydrogen being set free, manifests itself by rendering the oil black.
Hence the only way of preserving these oils colourless and transparent,
is by keeping them in bottles perfectly full and accurately corked, to
hinder the contact of air, which always discolours them.
Successive rectifications of this oil furnish another phenomenon
confirming our theory. In each distillation a small quantity of charcoal
remains in the retort, and a little water is formed by the union of the
oxygen contained in the air of the distilling vessels with the hydrogen
of the oil. As this takes place in each successive distillation, if we
make use of large vessels and a considerable degree of heat, we at last
decompose the whole of the oil, and change it entirely into water and
charcoal. When we use small vessels, and especially when we employ a
slow fire, or degree of heat little above that of boiling water, the
total decomposition of these oils, by repeated distillation, is greatly
more tedious, and more difficultly accomplished. I shall give a
particular detail to the Academy, in a separate memoir, of all my
experiments upon the decomposition of oil; but what I have related above
may suffice to give just ideas of the composition of animal and
vegetable substances, and of their decomposition by the action of fire.
FOOTNOTES:
[24] Though this term, red heat, does not indicate any absolutely
determinate degree of temperature, I shall use it sometimes to express a
temperature considerably above that of boiling water.--A.
[25] I must be understood here to speak of vegetables reduced to a
perfectly dry state; and, with respect to oil, I do not mean that which
is procured by expression either in the cold, or in a temperature not
exceeding that of boiling water; I only allude to the empyreumatic oil
procured by distillation with a naked fire, in a heat superior to the
temperature of boiling water; which is the only oil declared to be
produced by the operation of fire. What I have published upon this
subject in the Memoirs of the Academy for 1786 may be consulted.--A.
CHAP. XIII.
_Of the Decomposition of Vegetable Oxyds by the Vinous Fermentation._
The manner in which wine, cyder, mead, and all the liquors formed by the
spiritous fermentation, are produced, is well known to every one. The
juice of grapes or of apples being expressed, and the latter being
diluted with water, they are put into large vats, which are kept in a
temperature of at least 10 deg. (54.5 deg.) of the thermometer. A rapid
intestine motion, or fermentation, very soon takes place, numerous
globules of gas form in the liquid and burst at the surface; when the
fermentation is at its height, the quantity of gas disengaged is so
great as to make the liquor appear as if boiling violently over a fire.
When this gas is carefully gathered, it is found to be carbonic acid
perfectly pure, and free from admixture with any other species of air or
gas whatever.
When the fermentation is completed, the juice of grapes is changed from
being sweet, and full of sugar, into a vinous liquor which no longer
contains any sugar, and from which we procure, by distillation, an
inflammable liquor, known in commerce under the name of Spirit of Wine.
As this liquor is produced by the fermentation of any saccharine matter
whatever diluted with water, it must have been contrary to the
principles of our nomenclature to call it spirit of wine rather than
spirit of cyder, or of fermented sugar; wherefore, we have adopted a
more general term, and the Arabic word _alkohol_ seems extremely proper
for the purpose.
This operation is one of the most extraordinary in chemistry: We must
examine whence proceed the disengaged carbonic acid and the inflammable
liquor produced, and in what manner a sweet vegetable oxyd becomes thus
converted into two such opposite substances, whereof one is combustible,
and the other eminently the contrary. To solve these two questions, it
is necessary to be previously acquainted with the analysis of the
fermentable substance, and of the products of the fermentation. We may
lay it down as an incontestible axiom, that, in all the operations of
art and nature, nothing is created; an equal quantity of matter exists
both before and after the experiment; the quality and quantity of the
elements remain precisely the same; and nothing takes place beyond
changes and modifications in the combination of these elements. Upon
this principle the whole art of performing chemical experiments
depends: We must always suppose an exact equality between the elements
of the body examined and those of the products of its analysis.
Hence, since from must of grapes we procure alkohol and carbonic acid, I
have an undoubted right to suppose that must consists of carbonic acid
and alkohol. From these premises, we have two methods of ascertaining
what passes during vinous fermentation, by determining the nature of,
and the elements which compose, the fermentable substances, or by
accurately examining the produces resulting from fermentation; and it is
evident that the knowledge of either of these must lead to accurate
conclusions concerning the nature and composition of the other. From
these considerations, it became necessary accurately to determine the
constituent elements of the fermentable substances; and, for this
purpose, I did not make use of the compound juices of fruits, the
rigorous analysis of which is perhaps impossible, but made choice of
sugar, which is easily analysed, and the nature of which I have already
explained. This substance is a true vegetable oxyd with two bases,
composed of hydrogen and charcoal brought to the state of an oxyd, by a
certain proportion of oxygen; and these three elements are combined in
such a way, that a very slight force is sufficient to destroy the
equilibrium of their connection. By a long train of experiments, made
in various ways, and often repeated, I ascertained that the proportion
in which these ingredients exist in sugar, are nearly eight parts of
hydrogen, 64 parts of oxygen, and 28 parts of charcoal, all by weight,
forming 100 parts of sugar.
Sugar must be mixed with about four times its weight of water, to render
it susceptible of fermentation; and even then the equilibrium of its
elements would remain undisturbed, without the assistance of some
substance, to give a commencement to the fermentation. This is
accomplished by means of a little yeast from beer; and, when the
fermentation is once excited, it continues of itself until completed. I
shall, in another place, give an account of the effects of yeast, and
other ferments, upon fermentable substances. I have usually employed 10
libs. of yeast, in the state of paste, for each 100 libs. of sugar,
with as much water as is four times the weight of the sugar. I shall
give the results of my experiments exactly as they were obtained,
preserving even the fractions produced by calculation.
TABLE I. _Materials of Fermentation._
libs. oz. gros grs.
Water 400 0 0 0
Sugar 100 0 0 0
Yeast in paste, 10 libs. { Water 7 3 6 44
composed of { Dry yeast 2 12 1 28
----------------------
Total 510
TABLE II. _Constituent Elements of the Materials of Fermentation._
libs. oz. gros grs.
407 libs. 3 oz. 6 gros 44 grs. { Hydrogen 61 1 2 71.40
of water, composed of { Oxygen 346 2 3 44.60
{ Hydrogen 8 0 0 0
100 libs. sugar, composed of { Oxygen 64 0 0 0
{ Charcoal 28 0 0 0
{ Hydrogen 0 4 5 9.30
2 libs. 12 oz. 1 gros 28 grs. of { Oxygen 1 10 2 28.76
dry yeast, composed of { Charcoal 0 12 4 59
{ Azote 0 0 5 2.94
-----------------------
Total weight 510 0 0 0
TABLE III. _Recapitulation of these Elements._
libs. oz. gros grs.
Oxygen:
of the water 340 0 0 0 }
of the water } libs. oz. gros grs.
in the yeast 6 2 3 44.60 } 411 12 6 1.36
of the sugar 64 0 0 0 }
of the dry yeast 1 10 2 28.76 }
Hydrogen:
of the water 60 0 0 0 }
of the water }
in the yeast 1 1 2 71.40 } 69 6 0 8.70
of the sugar 8 0 0 0 }
of the dry yeast 0 4 5 9.30 }
Charcoal:
of the sugar 28 0 0 0 }
of the yeast 0 12 4 59.00 } 28 12 4 59.00
Azote of the yeast - - - - } 0 0 5 2.94
--------------------------
In all 510 0 0 0
Having thus accurately determined the nature and quantity of the
constituent elements of the materials submitted to fermentation, we have
next to examine the products resulting from that process. For this
purpose, I placed the above 510 libs. of fermentable liquor in a
proper[26] apparatus, by means of which I could accurately determine the
quantity and quality of gas disengaged during the fermentation, and
could even weigh every one of the products separately, at any period of
the process I judged proper. An hour or two after the substances are
mixed together, especially if they are kept in a temperature of from 15
deg. (65.75 deg.) to 18 deg. (72.5 deg.) of the thermometer, the first
marks of fermentation commence; the liquor turns thick and frothy, little
globules of air are disengaged, which rise and burst at the surface; the
quantity of these globules quickly increases, and there is a rapid and
abundant production of very pure carbonic acid, accompanied with a scum,
which is the yeast separating from the mixture. After some days, less or
more according to the degree of heat, the intestine motion and
disengagement of gas diminish; but these do not cease entirely, nor is
the fermentation completed for a considerable time. During the process,
35 libs. 5 oz. 4 gros 19 grs. of dry carbonic acid are
disengaged, which carry alongst with them 13 libs. 14 oz. 5 gros
of water. There remains in the vessel 460 libs. 11 oz. 6 gros 53
grs. of vinous liquor, slightly acidulous. This is at first muddy, but
clears of itself, and deposits a portion of yeast. When we separately
analise all these substances, which is effected by very troublesome
processes, we have the results as given in the following Tables. This
process, with all the subordinate calculations and analyses, will be
detailed at large in the Memoirs of the Academy.
TABLE IV. _Product of Fermentation._
libs. oz. gros grs.
35 libs. 5 oz. 4 gros 19 grs. { Oxygen 25 7 1 34
of carbonic acid, composed of { Charcoal 9 14 2 57
408 libs. 15 oz. 5 gros 14 grs. { Oxygen 347 10 0 59
of water, composed of { Hydrogen 61 5 4 27
{ Oxygen, combined
{ with hydrogen 31 6 1 64
{ Hydrogen, combined
57 libs. 11 oz. 1 gros 58 grs. { with oxygen 5 8 5 3
of dry alkohol, composed of { Hydrogen, combined
{ with charcoal 4 0 5 0
{ Charcoal, combined
{ with hydrogen 16 11 5 63
2 libs. 8 oz. of dry acetous { Hydrogen 0 2 4 0
acid, composed of { Oxygen 1 11 4 0
{ Charcoal 0 10 0 0
4 libs. 1 oz. 4 gros 3 grs. { Hydrogen 0 5 1 67
of residuum of sugar, { Oxygen 2 9 7 27
composed of { Charcoal 1 2 2 53
{ Hydrogen 0 2 2 41
1 lib. 6 oz. 0 gros 5 grs. { Oxygen 0 13 1 14
of dry yeast, composed of { Charcoal 0 6 2 30
{ Azote 0 0 2 37
--- -----------------
510 libs. Total 510 0 0 0
TABLE V. _Recapitulation of the Products._
----------------------------------------------------------------------------
libs. oz. gros grs.
409 libs. 10 oz. 0 gros 54 grs. { Water 347 10 0 59
of oxygen contained in the { Carbonic acid 25 7 1 34
{ Alkohol 31 6 1 64
{ Acetous acid 1 11 4 0
{ Residuum of sugar 2 9 7 27
{ Yeast 0 13 1 14
28 libs. 12 oz. 5 gros 59 grs. { Carbonic acid 9 14 2 57
of charcoal contained { Alkohol 16 11 5 63
in the { Acetous acid 0 10 0 0
{ Residuum of sugar 1 2 2 53
{ Yeast 0 6 2 30
{ Water 61 5 4 27
71 libs. 8 oz. 6 gros 66 grs. { Water of the alkohol 5 8 5 3
of hydrogen contained { Combined with the
in the { charcoal of the alko. 4 0 5 0
{ Acetous acid 0 2 4 0
{ Residuum of sugar 0 5 1 67
{ Yeast 0 2 2 41
2 gros 37 grs. of azote in the yeast 0 0 2 37
--- ---------------
510 libs. Total 510 0 0 0
In these results, I have been exact, even to grains; not that it is
possible, in experiments of this nature, to carry our accuracy so far,
but as the experiments were made only with a few pounds of sugar, and
as, for the sake of comparison, I reduced the results of the actual
experiments to the quintal or imaginary hundred pounds, I thought it
necessary to leave the fractional parts precisely as produced by
calculation.
When we consider the results presented by these tables with attention,
it is easy to discover exactly what occurs during fermentation. In the
first place, out of the 100 libs. of sugar employed, 4 libs. 1 oz.
4 gros 3 grs. remain, without having suffered decomposition; so
that, in reality, we have only operated upon 95 libs. 14 oz. 3
gros 69 grs. of sugar; that is to say, upon 61 libs. 6 oz. 45
grs. of oxygen, 7 libs. 10 oz. 6 gros 6 grs. of hydrogen, and
26 libs. 13 oz. 5 gros 19 grs. of charcoal. By comparing these
quantities, we find that they are fully sufficient for forming the whole
of the alkohol, carbonic acid and acetous acid produced by the
fermentation. It is not, therefore, necessary to suppose that any water
has been decomposed during the experiment, unless it be pretended that
the oxygen and hydrogen exist in the sugar in that state. On the
contrary, I have already made it evident that hydrogen, oxygen and
charcoal, the three constituent elements of vegetables, remain in a
state of equilibrium or mutual union with each other which subsists so
long as this union remains undisturbed by increased temperature, or by
some new compound attraction; and that then only these elements
combine, two and two together, to form water and carbonic acid.
The effects of the vinous fermentation upon sugar is thus reduced to the
mere separation of its elements into two portions; one part is
oxygenated at the expence of the other, so as to form carbonic acid,
whilst the other part, being deoxygenated in favour of the former, is
converted into the combustible substance alkohol; therefore, if it were
possible to reunite alkohol and carbonic acid together, we ought to form
sugar. It is evident that the charcoal and hydrogen in the alkohol do
not exist in the state of oil, they are combined with a portion of
oxygen, which renders them miscible with water; wherefore these three
substances, oxygen, hydrogen, and charcoal, exist here likewise in a
species of equilibrium or reciprocal combination; and in fact, when they
are made to pass through a red hot tube of glass or porcelain, this
union or equilibrium is destroyed, the elements become combined, two and
two, and water and carbonic acid are formed.
I had formally advanced, in my first Memoirs upon the formation of
water, that it was decomposed in a great number of chemical experiments,
and particularly during the vinous fermentation. I then supposed that
water existed ready formed in sugar, though I am now convinced that
sugar only contains the elements proper for composing it. It may be
readily conceived, that it must have cost me a good deal to abandon my
first notions, but by several years reflection, and after a great number
of experiments and observations upon vegetable substances, I have fixed
my ideas as above.
I shall finish what I have to say upon vinous fermentation, by
observing, that it furnishes us with the means of analysing sugar and
every vegetable fermentable matter. We may consider the substances
submitted to fermentation, and the products resulting from that
operation, as forming an algebraic equation; and, by successively
supposing each of the elements in this equation unknown, we can
calculate their values in succession, and thus verify our experiments by
calculation, and our calculation by experiment reciprocally. I have
often successfully employed this method for correcting the first results
of my experiments, and to direct me in the proper road for repeating
them to advantage. I have explained myself at large upon this subject,
in a Memoir upon vinous fermentation already presented to the Academy,
and which will speedily be published.
FOOTNOTES:
[26] The above apparatus is described in the Third Part.--A.
CHAP. XIV.
_Of the Putrefactive Fermentation._
The phenomena of putrefaction are caused, like those of vinous
fermentation, by the operation of very complicated affinities. The
constituent elements of the bodies submitted to this process cease to
continue in equilibrium in the threefold combination, and form
themselves anew into binary combinations[27], or compounds, consisting
of two elements only; but these are entirely different from the results
produced by the vinous fermentation. Instead of one part of the hydrogen
remaining united with part of the water and charcoal to form alkohol, as
in the vinous fermentation, the whole of the hydrogen is dissipated,
during putrefaction, in the form of hydrogen gas, whilst, at the same
time, the oxygen and charcoal, uniting with caloric, escape in the form
of carbonic acid gas; so that, when the whole process is finished,
especially if the materials have been mixed with a sufficient quantity
of water, nothing remains but the earth of the vegetable mixed with a
small portion of charcoal and iron. Thus putrefaction is nothing more
than a complete analysis of vegetable substance, during which the whole
of the constituent elements is disengaged in form of gas, except the
earth, which remains in the state of mould[28].
Such is the result of putrefaction when the substances submitted to it
contain only oxygen, hydrogen, charcoal and a little earth. But this
case is rare, and these substances putrify imperfectly and with
difficulty, and require a considerable time to complete their
putrefaction. It is otherwise with substances containing azote, which
indeed exists in all animal matters, and even in a considerable number
of vegetable substances. This additional element is remarkably
favourable to putrefaction; and for this reason animal matter is mixed
with vegetable, when the putrefaction of these is wished to be hastened.
The whole art of forming composts and dunghills, for the purposes of
agriculture, consists in the proper application of this admixture.
The addition of azote to the materials of putrefaction not only
accelerates the process, that element likewise combines with part of
the hydrogen, and forms a new substance called _volatile alkali_ or
_ammoniac_. The results obtained by analysing animal matters, by
different processes, leave no room for doubt with regard to the
constituent elements of ammoniac; whenever the azote has been previously
separated from these substances, no ammoniac is produced; and in all
cases they furnish ammoniac only in proportion to the azote they
contain. This composition of ammoniac is likewise fully proved by Mr
Berthollet, in the Memoirs of the Academy for 1785, p. 316. where he
gives a variety of analytical processes by which ammoniac is decomposed,
and its two elements, azote and hydrogen, procured separately.
I already mentioned in Chap. X. that almost all combustible bodies were
capable of combining with each other; hydrogen gas possesses this
quality in an eminent degree, it dissolves charcoal, sulphur, and
phosphorus, producing the compounds named _carbonated hydrogen gas_,
_sulphurated hydrogen gas_, and _phosphorated hydrogen gas_. The two
latter of these gasses have a peculiarly disagreeable flavour; the
sulphurated hydrogen gas has a strong resemblance to the smell of rotten
eggs, and the phosphorated smells exactly like putrid fish. Ammoniac has
likewise a peculiar odour, not less penetrating, or less disagreeable,
than these other gasses. From the mixture of these different flavours
proceeds the fetor which accompanies the putrefaction of animal
substances. Sometimes ammoniac predominates, which is easily perceived
by its sharpness upon the eyes; sometimes, as in feculent matters, the
sulphurated gas is most prevalent; and sometimes, as in putrid herrings,
the phosphorated hydrogen gas is most abundant.
I long supposed that nothing could derange or interrupt the course of
putrefaction; but Mr Fourcroy and Mr Thouret have observed some peculiar
phenomena in dead bodies, buried at a certain depth, and preserved to a
certain degree, from contact with air; having found the muscular flesh
frequently converted into true animal fat. This must have arisen from
the disengagement of the azote, naturally contained in the animal
substance, by some unknown cause, leaving only the hydrogen and charcoal
remaining, which are the elements proper for producing fat or oil. This
observation upon the possibility of converting animal substances into
fat may some time or other lead to discoveries of great importance to
society. The faeces of animals, and other excrementitious matters, are
chiefly composed of charcoal and hydrogen, and approach considerably to
the nature of oil, of which they furnish a considerable quantity by
distillation with a naked fire; but the intolerable foetor which
accompanies all the products of these substances prevents our expecting
that, at least for a long time, they can be rendered useful in any other
way than as manures.
I have only given conjectural approximations in this Chapter upon the
composition of animal substances, which is hitherto but imperfectly
understood. We know that they are composed of hydrogen, charcoal, azote,
phosphorus, and sulphur, all of which, in a state of quintuple
combination, are brought to the state of oxyd by a larger or smaller
quantity of oxygen. We are, however, still unacquainted with the
proportions in which these substances are combined, and must leave it to
time to complete this part of chemical analysis, as it has already done
with several others.
FOOTNOTES:
[27] Binary combinations are such as consist of two simple elements
combined together. Ternary, and quaternary, consist of three and four
elements.--E.
[28] In the Third Part will be given the description of an apparatus
proper for being used in experiments of this kind.--A.
CHAP. XV.
_Of the Acetous Fermentation._
The acetous fermentation is nothing more than the acidification or
oxygenation of wine[29], produced in the open air by means of the
absorption of oxygen. The resulting acid is the acetous acid, commonly
called Vinegar, which is composed of hydrogen and charcoal united
together in proportions not yet ascertained, and changed into the acid
state by oxygen. As vinegar is an acid, we might conclude from analogy
that it contains oxygen, but this is put beyond doubt by direct
experiments: In the first place, we cannot change wine into vinegar
without the contact of air containing oxygen; secondly, this process is
accompanied by a diminution of the volume of the air in which it is
carried on from the absorption of its oxygen; and, thirdly, wine may be
changed into vinegar by any other means of oxygenation.
Independent of the proofs which these facts furnish of the acetous acid
being produced by the oxygenation of wine, an experiment made by Mr
Chaptal, Professor of Chemistry at Montpellier, gives us a distinct view
of what takes place in this process. He impregnated water with about its
own bulk of carbonic acid from fermenting beer, and placed this water in
a cellar in vessels communicating with the air, and in a short time the
whole was converted into acetous acid. The carbonic acid gas procured
from beer vats in fermentation is not perfectly pure, but contains a
small quantity of alkohol in solution, wherefore water impregnated with
it contains all the materials necessary for forming the acetous acid.
The alkohol furnishes hydrogen and one portion of charcoal, the carbonic
acid furnishes oxygen and the rest of the charcoal, and the air of the
atmosphere furnishes the rest of the oxygen necessary for changing the
mixture into acetous acid. From this observation it follows, that
nothing but hydrogen is wanting to convert carbonic acid into acetous
acid; or more generally, that, by means of hydrogen, and according to
the degree of oxygenation, carbonic acid may be changed into all the
vegetable acids; and, on the contrary, that, by depriving any of the
vegetable acids of their hydrogen, they may be converted into carbonic
acid.
Although the principal facts relating to the acetous acid are well
known, yet numerical exactitude is still wanting, till furnished by more
exact experiments than any hitherto performed; wherefore I shall not
enlarge any farther upon the subject. It is sufficiently shown by what
has been said, that the constitution of all the vegetable acids and
oxyds is exactly conformable to the formation of vinegar; but farther
experiments are necessary to teach us the proportion of the constituent
elements in all these acids and oxyds. We may easily perceive, however,
that this part of chemistry, like all the rest of its divisions, makes
rapid progress towards perfection, and that it is already rendered
greatly more simple than was formerly believed.
FOOTNOTES:
[29] The word Wine, in this chapter, is used to signify the liquor
produced by the vinous fermentation, whatever vegetable substance may
have been used for obtaining it.--E.
CHAP. XVI.
_Of the Formation of Neutral Salts, and of their different Bases._
We have just seen that all the oxyds and acids from the animal and
vegetable kingdoms are formed by means of a small number of simple
elements, or at least of such as have not hitherto been susceptible of
decomposition, by means of combination with oxygen; these are azote,
sulphur, phosphorus, charcoal, hydrogen, and the muriatic radical[30].
We may justly admire the simplicity of the means employed by nature to
multiply qualities and forms, whether by combining three or four
acidifiable bases in different proportions, or by altering the dose of
oxygen employed for oxydating or acidifying them. We shall find the
means no less simple and diversified, and as abundantly productive of
forms and qualities, in the order of bodies we are now about to treat
of.
Acidifiable substances, by combining with oxygen, and their consequent
conversion into acids, acquire great susceptibility of farther
combination; they become capable of uniting with earthy and metallic
bodies, by which means neutral salts are formed. Acids may therefore be
considered as true _salifying_ principles, and the substances with which
they unite to form neutral salts may be called _salifiable_ bases: The
nature of the union which these two principles form with each other is
meant as the subject of the present chapter.
This view of the acids prevents me from considering them as salts,
though they are possessed of many of the principal properties of saline
bodies, as solubility in water, &c. I have already observed that they
are the result of a first order of combination, being composed of two
simple elements, or at least of elements which act as if they were
simple, and we may therefore rank them, to use the language of Stahl, in
the order of _mixts_. The neutral salts, on the contrary, are of a
secondary order of combination, being formed by the union of two _mixts_
with each other, and may therefore be termed _compounds_. Hence I shall
not arrange the alkalies[31] or earths in the class of salts, to which
I allot only such as are composed of an oxygenated substance united to
a base.
I have already enlarged sufficiently upon the formation of acids in the
preceding chapter, and shall not add any thing farther upon that
subject; but having as yet given no account of the salifiable bases
which are capable of uniting with them to form neutral salts, I mean, in
this chapter, to give an account of the nature and origin of each of
these bases. These are potash, soda, ammoniac, lime, magnesia, barytes,
argill[32], and all the metallic bodies.
Sec. 1. _Of Potash._
We have already shown, that, when a vegetable substance is submitted to
the action of fire in distilling vessels, its component elements,
oxygen, hydrogen, and charcoal, which formed a threefold combination in
a state of equilibrium, unite, two and two, in obedience to affinities
which act conformable to the degree of heat employed. Thus, at the
first application of the fire, whenever the heat produced exceeds the
temperature of boiling water, part of the oxygen and hydrogen unite to
form water; soon after the rest of the hydrogen, and part of the
charcoal, combine into oil; and, lastly, when the fire is pushed to the
red heat, the oil and water, which had been formed in the early part of
the process, become again decomposed, the oxygen and charcoal unite to
form carbonic acid, a large quantity of hydrogen gas is set free, and
nothing but charcoal remains in the retort.
A great part of these phenomena occur during the combustion of
vegetables in the open air; but, in this case, the presence of the air
introduces three new substances, the oxygen and azote of the air and
caloric, of which two at least produce considerable changes in the
results of the operation. In proportion as the hydrogen of the
vegetable, or that which results from the decomposition of the water, is
forced out in the form of hydrogen gas by the progress of the fire, it
is set on fire immediately upon getting in contact with the air, water
is again formed, and the greater part of the caloric of the two gasses
becoming free produces flame. When all the hydrogen gas is driven out,
burnt, and again reduced to water, the remaining charcoal continues to
burn, but without flame; it is formed into carbonic acid, which carries
off a portion of caloric sufficient to give it the gasseous form; the
rest of the caloric, from the oxygen of the air, being set free,
produces the heat and light observed during the combustion of charcoal.
The whole vegetable is thus reduced into water and carbonic acid, and
nothing remains but a small portion of gray earthy matter called ashes,
being the only really fixed principles which enter into the constitution
of vegetables.
The earth, or rather ashes, which seldom exceeds a twentieth part of the
weight of the vegetable, contains a substance of a particular nature,
known under the name of fixed vegetable alkali, or potash. To obtain it,
water is poured upon the ashes, which dissolves the potash, and leaves
the ashes which are insoluble; by afterwards evaporating the water, we
obtain the potash in a white concrete form: It is very fixed even in a
very high degree of heat. I do not mean here to describe the art of
preparing potash, or the method of procuring it in a state of purity,
but have entered upon the above detail that I might not use any word not
previously explained.
The potash obtained by this process is always less or more saturated
with carbonic acid, which is easily accounted for: As the potash does
not form, or at least is not set free, but in proportion as the
charcoal of the vegetable is converted into carbonic acid by the
addition of oxygen, either from the air or the water, it follows, that
each particle of potash, at the instant of its formation, or at least of
its liberation, is in contact with a particle of carbonic acid, and, as
there is a considerable affinity between these two substances, they
naturally combine together. Although the carbonic acid has less affinity
with potash than any other acid, yet it is difficult to separate the
last portions from it. The most usual method of accomplishing this is to
dissolve the potash in water; to this solution add two or three times
its weight of quick-lime, then filtrate the liquor and evaporate it in
close vessels; the saline substance left by the evaporation is potash
almost entirely deprived of carbonic acid. In this state it is soluble
in an equal weight of water, and even attracts the moisture of the air
with great avidity; by this property it furnishes us with an excellent
means of rendering air or gas dry by exposing them to its action. In
this state it is soluble in alkohol, though not when combined with
carbonic acid; and Mr Berthollet employs this property as a method of
procuring potash in the state of perfect purity.
All vegetables yield less or more of potash in consequence of
combustion, but it is furnished in various degrees of purity by
different vegetables; usually, indeed, from all of them it is mixed
with different salts from which it is easily separable. We can hardly
entertain a doubt that the ashes, or earth which is left by vegetables
in combustion, pre-existed in them before they were burnt, forming what
may be called the skeleton, or osseous part of the vegetable. But it is
quite otherwise with potash; this substance has never yet been procured
from vegetables but by means of processes or intermedia capable of
furnishing oxygen and azote, such as combustion, or by means of nitric
acid; so that it is not yet demonstrated that potash may not be a
produce from these operations. I have begun a series of experiments upon
this object, and hope soon to be able to give an account of their
results.
Sec. 2. _Of Soda._
Soda, like potash, is an alkali procured by lixiviation from the ashes
of burnt plants, but only from those which grow upon the sea-side, and
especially from the herb _kali_, whence is derived the name _alkali_,
given to this substance by the Arabians. It has some properties in
common with potash, and others which are entirely different: In general,
these two substances have peculiar characters in their saline
combinations which are proper to each, and consequently distinguish them
from each other; thus soda, which, as obtained from marine plants, is
usually entirely saturated with carbonic acid, does not attract the
humidity of the atmosphere like potash, but, on the contrary,
desiccates, its cristals effloresce, and are converted into a white
powder having all the properties of soda, which it really is, having
only lost its water of cristallization.
Hitherto we are not better acquainted with the constituent elements of
soda than with those of potash, being equally uncertain whether it
previously existed ready formed in the vegetable or is a combination of
elements effected by combustion. Analogy leads us to suspect that azote
is a constituent element of all the alkalies, as is the case with
ammoniac; but we have only slight presumptions, unconfirmed by any
decisive experiments, respecting the composition of potash and soda.
Sec. 3. _Of Ammoniac._
We have, however, very accurate knowledge of the composition of
ammoniac, or volatile alkali, as it is called by the old chemists. Mr
Berthollet, in the Memoirs of the Academy for 1784, p. 316. has proved
by analysis, that 1000 parts of this substance consist of about 807
parts of azote combined with 193 parts of hydrogen.
Ammoniac is chiefly procurable from animal substances by distillation,
during which process the azote and hydrogen necessary to its formation
unite in proper proportions; it is not, however, procured pure by this
process, being mixed with oil and water, and mostly saturated with
carbonic acid. To separate these substances it is first combined with an
acid, the muriatic for instance, and then disengaged from that
combination by the addition of lime or potash. When ammoniac is thus
produced in its greatest degree of purity it can only exist under the
gasseous form, at least in the usual temperature of the atmosphere, it
has an excessively penetrating smell, is absorbed in large quantities by
water, especially if cold and assisted by compression. Water thus
saturated with ammoniac has usually been termed volatile alkaline fluor;
we shall call it either simply ammoniac, or liquid ammoniac, and
ammoniacal gas when it exists in the aeriform state.
Sec. 4. _Of Lime, Magnesia, Barytes, and Argill._
The composition of these four earths is totally unknown, and, until by
new discoveries their constituent elements are ascertained, we are
certainly authorised to consider them as simple bodies. Art has no share
in the production of these earths, as they are all procured ready
formed from nature; but, as they have all, especially the three first,
great tendency to combination, they are never found pure. Lime is
usually saturated with carbonic acid in the state of chalk, calcarious
spars, most of the marbles, &c.; sometimes with sulphuric acid, as in
gypsum and plaster stones; at other times with fluoric acid forming
vitreous or fluor spars; and, lastly, it is found in the waters of the
sea, and of saline springs, combined with muriatic acid. Of all the
salifiable bases it is the most universally spread through nature.
Magnesia is found in mineral waters, for the most part combined with
sulphuric acid; it is likewise abundant in sea-water, united with
muriatic acid; and it exists in a great number of stones of different
kinds.
Barytes is much less common than the three preceding earths; it is found
in the mineral kingdom, combined with sulphuric acid, forming heavy
spars, and sometimes, though rarely, united to carbonic acid.
Argill, or the base of alum, having less tendency to combination than
the other earths, is often found in the state of argill, uncombined with
any acid. It is chiefly procurable from clays, of which, properly
speaking, it is the base, or chief ingredient.
Sec. 5. _Of Metallic Bodies._
The metals, except gold, and sometimes silver, are rarely found in the
mineral kingdom in their metallic state, being usually less or more
saturated with oxygen, or combined with sulphur, arsenic, sulphuric
acid, muriatic acid, carbonic acid, or phosphoric acid. Metallurgy, or
the docimastic art, teaches the means of separating them from these
foreign matters; and for this purpose we refer to such chemical books as
treat upon these operations.
We are probably only acquainted as yet with a part of the metallic
substances existing in nature, as all those which have a stronger
affinity to oxygen, than charcoal possesses, are incapable of being
reduced to the metallic state, and, consequently, being only presented
to our observation under the form of oxyds, are confounded with earths.
It is extremely probable that barytes, which we have just now arranged
with earths, is in this situation; for in many experiments it exhibits
properties nearly approaching to those of metallic bodies. It is even
possible that all the substances we call earths may be only metallic
oxyds, irreducible by any hitherto known process.
Those metallic bodies we are at present acquainted with, and which we
can reduce to the metallic or reguline state, are the following
seventeen:
1. Arsenic.
2. Molybdena.
3. Tungstein.
4. Manganese.
5. Nickel.
6. Cobalt.
7. Bismuth.
8. Antimony.
9. Zinc.
10. Iron.
11. Tin.
12. Lead.
13. Copper.
14. Mercury.
15. Silver.
16. Platina.
17. Gold.
I only mean to consider these as salifiable bases, without entering at
all upon the consideration of their properties in the arts, and for the
uses of society. In these points of view each metal would require a
complete treatise, which would lead me far beyond the bounds I have
prescribed for this work.
FOOTNOTES:
[30] I have not ventured to omit this element, as here enumerated with
the other principles of animal and vegetable substances, though it is
not at all taken notice of in the preceding chapters as entering into
the composition of these bodies.--E.
[31] Perhaps my thus rejecting the alkalies from the class of salts may
be considered as a capital defect in the method I have adopted, and I am
ready to admit the charge; but this inconvenience is compensated by so
many advantages, that I could not think it of sufficient consequence to
make me alter my plan.--A.
[32] Called Alumine by Mr Lavoisier; but as Argill has been in a manner
naturalized to the language for this substance by Mr Kirwan, I have
ventured to use it in preference.--E.
CHAP. XVII.
_Continuation of the Observations upon Salifiable Bases, and the
Formation of Neutral Salts._
It is necessary to remark, that earths and alkalies unite with acids to
form neutral salts without the intervention of any medium, whereas
metallic substances are incapable of forming this combination without
being previously less or more oxygenated; strictly speaking, therefore,
metals are not soluble in acids, but only metallic oxyds. Hence, when we
put a metal into an acid for solution, it is necessary, in the first
place, that it become oxygenated, either by attracting oxygen from the
acid or from the water; or, in other words, that a metal cannot be
dissolved in an acid unless the oxygen, either of the acid, or of the
water mixed with it, has a stronger affinity to the metal than to the
hydrogen or the acidifiable base; or, what amounts to the same thing,
that no metallic solution can take place without a previous
decomposition of the water, or the acid in which it is made. The
explanation of the principal phenomena of metallic solution depends
entirely upon this simple observation, which was overlooked even by the
illustrious Bergman.
The first and most striking of these is the effervescence, or, to speak
less equivocally, the disengagement of gas which takes place during the
solution; in the solutions made in nitric acid this effervescence is
produced by the disengagement of nitrous gas; in solutions with
sulphuric acid it is either sulphurous acid gas or hydrogen gas,
according as the oxydation of the metal happens to be made at the
expence of the sulphuric acid or of the water. As both nitric acid and
water are composed of elements which, when separate, can only exist in
the gasseous form, at least in the common temperature of the atmosphere,
it is evident that, whenever either of these is deprived of its oxygen,
the remaining element must instantly expand and assume the state of gas;
the effervescence is occasioned by this sudden conversion from the
liquid to the gasseous state. The same decomposition, and consequent
formation of gas, takes place when solutions of metals are made in
sulphuric acid: In general, especially by the humid way, metals do not
attract all the oxygen it contains; they therefore reduce it, not into
sulphur, but into sulphurous acid, and as this acid can only exist as
gas in the usual temperature, it is disengaged, and occasions
effervescence.
The second phenomenon is, that, when the metals have been previously
oxydated, they all dissolve in acids without effervescence: This is
easily explained; because, not having now any occasion for combining
with oxygen, they neither decompose the acid nor the water by which, in
the former case, the effervescence is occasioned.
A third phenomenon, which requires particular consideration, is, that
none of the metals produce effervescence by solution in oxygenated
muriatic acid. During this process the metal, in the first place,
carries off the excess of oxygen from the oxygenated muriatic acid, by
which it becomes oxydated, and reduces the acid to the state of ordinary
muriatic acid. In this case there is no production of gas, not that the
muriatic acid does not tend to exist in the gasseous state in the common
temperature, which it does equally with the acids formerly mentioned,
but because this acid, which otherwise would expand into gas, finds more
water combined with the oxygenated muriatic acid than is necessary to
retain it in the liquid form; hence it does not disengage like the
sulphurous acid, but remains, and quietly dissolves and combines with
the metallic oxyd previously formed from its superabundant oxygen.
The fourth phenomenon is, that metals are absolutely insoluble in such
acids as have their bases joined to oxygen by a stronger affinity than
these metals are capable of exerting upon that acidifying principle.
Hence silver, mercury, and lead, in their metallic states, are insoluble
in muriatic acid, but, when previously oxydated, they become readily
soluble without effervescence.
From these phenomena it appears that oxygen is the bond of union between
metals and acids; and from this we are led to suppose that oxygen is
contained in all substances which have a strong affinity with acids:
Hence it is very probable the four eminently salifiable earths contain
oxygen, and their capability of uniting with acids is produced by the
intermediation of that element. What I have formerly noticed relative to
these earths is considerably strengthened by the above considerations,
viz. that they may very possibly be metallic oxyds, with which oxygen
has a stronger affinity than with charcoal, and consequently not
reducible by any known means.
All the acids hitherto known are enumerated in the following table, the
first column of which contains the names of the acids according to the
new nomenclature, and in the second column are placed the bases or
radicals of these acids, with observations.
_Names of the Acids._ _Names of the Bases, with Observations._
1. Sulphurous }Sulphur.
2. Sulphuric }
3. Phosphorous }Phosphorus.
4. Phosphoric }
5. Muriatic }Muriatic radical or base, hitherto unknown.
6. Oxygenated muriatic }
7. Nitrous }
8. Nitric }Azote.
9. Oxygenated nitric }
10. Carbonic Charcoal
}The bases or radicals of all these acids
11. Acetous }seem to be formed by a combination
12. Acetic }of charcoal and hydrogen;
13. Oxalic }and the only difference seems to be
14. Tartarous }owing to the different proportions in
15. Pyro-tartarous }which these elements combine to form
16. Citric }their bases, and to the different doses
17. Malic }of oxygen in their acidification. A
18. Pyro-lignous }connected series of accurate experiments
19. Pyro-mucous }is still wanted upon this subject.
20. Gallic }Our knowledge of the bases of
21. Prussic }these acids is hitherto imperfect; we
22. Benzoic }only know that they contain hydrogen
23. Succinic }and charcoal as principal elements,
24. Camphoric }and that the prussic acid contains
25. Lactic }azote.
26. Saccholactic }
27. Bombic }The base of these and all acids
28. Formic }procured from animal substances seems
29. Sebacic }to consist of charcoal, hydrogen,
}phosphorous, and azote.
30. Boracic }The bases of these two are hitherto
31. Fluoric }entirely unknown.
32. Antimonic Antimony.
33. Argentic Silver.
34. Arseniac(A) Arsenic.
35. Bismuthic Bismuth.
36. Cobaltic Cobalt.
37. Cupric Copper.
38. Stannic Tin.
39. Ferric Iron.
40. Manganic Manganese.
41. Mercuric(B) Mercury.
42. Molybdic Molybdena.
43. Nickolic Nickel.
44. Auric Gold.
45. Platinic Platina.
46. Plumbic Lead.
47. Tungstic Tungstein.
48. Zincic Zinc.
[Note A: This term swerves a little from the rule in making the name of
this acid terminate in _ac_ instead of _ic_. The base and acid are
distinguished in French by _arsenic_ and _arsenique_; but, having chosen
the English termination _ic_ to translate the French _ique_, I was
obliged to use this small deviation.--E.]
[Note B: Mr Lavoisier has hydrargirique; but mercurius being used for
the base or metal, the name of the acid, as above, is equally regular,
and less harsh.--E.]
In this list, which contains 48 acids, I have enumerated 17 metallic
acids hitherto very imperfectly known, but upon which Mr Berthollet is
about to publish a very important work. It cannot be pretended that all
the acids which exist in nature, or rather all the acidifiable bases,
are yet discovered; but, on the other hand, there are considerable
grounds for supposing that a more accurate investigation than has
hitherto been attempted will diminish the number of the vegetable acids,
by showing that several of these, at present considered as distinct
acids, are only modifications of others. All that can be done in the
present state of our knowledge is, to give a view of chemistry as it
really is, and to establish fundamental principles, by which such bodies
as may be discovered in future may receive names, in conformity with one
uniform system.
The known salifiable bases, or substances capable of being converted
into neutral salts by union with acids, amount to 24; viz. 3 alkalies, 4
earths, and 17 metallic substances; so that, in the present state of
chemical knowledge, the whole possible number of neutral salts amounts
to 1152[33]. This number is upon the supposition that the metallic acids
are capable of dissolving other metals, which is a new branch of
chemistry not hitherto investigated, upon which depends all the metallic
combinations named _vitreous_. There is reason to believe that many of
these supposable saline combinations are not capable of being formed,
which must greatly reduce the real number of neutral salts producible by
nature and art. Even if we suppose the real number to amount only to
five or six hundred species of possible neutral salts, it is evident
that, were we to distinguish them, after the manner of the ancients,
either by the names of their first discoverers, or by terms derived from
the substances from which they are procured, we should at last have such
a confusion of arbitrary designations, as no memory could possibly
retain. This method might be tolerable in the early ages of chemistry,
or even till within these twenty years, when only about thirty species
of salts were known; but, in the present times, when the number is
augmenting daily, when every new acid gives us 24 or 48 new salts,
according as it is capable of one or two degrees of oxygenation, a new
method is certainly necessary. The method we have adopted, drawn from
the nomenclature of the acids, is perfectly analogical, and, following
nature in the simplicity of her operations, gives a natural and easy
nomenclature applicable to every possible neutral salt.
In giving names to the different acids, we express the common property
by the generical term _acid_, and distinguish each species by the name
of its peculiar acidifiable base. Hence the acids formed by the
oxygenation of sulphur, phosphorus, charcoal, &c. are called _sulphuric
acid_, _phosphoric acid_, _carbonic acid_, &c. We thought it likewise
proper to indicate the different degrees of saturation with oxygen, by
different terminations of the same specific names. Hence we distinguish
between sulphurous and sulphuric, and between phosphorous and phosphoric
acids, &c.
By applying these principles to the nomenclature of neutral salts, we
give a common term to all the neutral salts arising from the combination
of one acid, and distinguish the species by adding the name of the
salifiable base. Thus, all the neutral salts having sulphuric acid in
their composition are named _sulphats_; those formed by the phosphoric
acid, _phosphats_, &c. The species being distinguished by the names of
the salifiable bases gives us _sulphat of potash_, _sulphat of soda_,
_sulphat of ammoniac_, _sulphat of lime_, _sulphat of iron_, &c. As we
are acquainted with 24 salifiable bases, alkaline, earthy, and metallic,
we have consequently 24 sulphats, as many phosphats, and so on through
all the acids. Sulphur is, however, susceptible of two degrees of
oxygenation, the first of which produces sulphurous, and the second,
sulphuric acid; and, as the neutral salts produced by these two acids,
have different properties, and are in fact different salts, it becomes
necessary to distinguish these by peculiar terminations; we have
therefore distinguished the neutral salts formed by the acids in the
first or lesser degree of oxygenation, by changing the termination _at_
into _ite_, as _sulphites_, _phosphites_[34], &c. Thus, oxygenated or
acidified sulphur, in its two degrees of oxygenation is capable of
forming 48 neutral salts, 24 of which are sulphites, and as many
sulphats; which is likewise the case with all the acids capable of two
degrees of oxygenation[35].
It were both tiresome and unnecessary to follow these denominations
through all the varieties of their possible application; it is enough to
have given the method of naming the various salts, which, when once well
understood, is easily applied to every possible combination. The name of
the combustible and acidifiable body being once known, the names of the
acid it is capable of forming, and of all the neutral combinations the
acid is susceptible of entering into, are most readily remembered. Such
as require a more complete illustration of the methods in which the new
nomenclature is applied will, in the Second Part of this book, find
Tables which contain a full enumeration of all the neutral salts, and,
in general, all the possible chemical combinations, so far as is
consistent with the present state of our knowledge. To these I shall
subjoin short explanations, containing the best and most simple means of
procuring the different species of acids, and some account of the
general properties of the neutral salts they produce.
I shall not deny, that, to render this work more complete, it would have
been necessary to add particular observations upon each species of salt,
its solubility in water and alkohol, the proportions of acid and of
salifiable base in its composition, the quantity of its water of
cristallization, the different degrees of saturation it is susceptible
of, and, finally, the degree of force or affinity with which the acid
adheres to the base. This immense work has been already begun by Messrs
Bergman, Morveau, Kirwan, and other celebrated chemists, but is hitherto
only in a moderate state of advancement, even the principles upon which
it is founded are not perhaps sufficiently accurate.
These numerous details would have swelled this elementary treatise to
much too great a size; besides that, to have gathered the necessary
materials, and to have completed all the series of experiments
requisite, must have retarded the publication of this book for many
years. This is a vast field for employing the zeal and abilities of
young chemists, whom I would advise to endeavour rather to do well than
to do much, and to ascertain, in the first place, the composition of the
acids, before entering upon that of the neutral salts. Every edifice
which is intended to resist the ravages of time should be built upon a
sure foundation; and, in the present state of chemistry, to attempt
discoveries by experiments, either not perfectly exact, or not
sufficiently rigorous, will serve only to interrupt its progress,
instead of contributing to its advancement.
FOOTNOTES:
[33] This number excludes all triple salts, or such as contain more than
one salifiable base, all the salts whose bases are over or under
saturated with acid, and those formed by the nitro-muriatic acid.--E.
[34] As all the specific names of the acids in the new nomenclature are
adjectives, they would have applied severally to the various salifiable
bases, without the invention of other terms, with perfect distinctness.
Thus, _sulphurous potash_, and _sulphuric potash_, are equally distinct
as _sulphite of potash_, and _sulphat of potash_; and have the advantage
of being more easily retained in the memory, because more naturally
arising from the acids themselves, than the arbitrary terminations
adopted by Mr Lavoisier.--E.
[35] There is yet a third degree of oxygenation of acids, as the
oxygenated muriatic and oxygenated nitric acids. The terms applicable to
the neutral salts resulting from the union of these acids with
salifiable bases is supplied by the Author in the Second Part of this
Work. These are formed by prefixing the word _oxygenated_ to the name of
the salt produced by the second degree of oxygenation. Thus,
_oxygenated_ muriat of potash, _oxygenated_ nitrat of soda, &c.--E.