submitted to the action of dilute sulphuric acid, it is dissolved in
the form of an oxide; it is in fact burned at the expense of the
oxygen contained in the fluid. A consequence of this action is the
production of an electric current, which, if conducted through a
wire, renders it magnetic. In thus effecting the solution of a pound
weight, for example, of zinc, we obtain a definite amount of force
adequate to raise a given weight one inch, and to keep it suspended;
and the amount of weight it will be capable of suspending will be
the greater the more rapidly the zinc is dissolved.
By alternately interrupting and renewing the contact of the zinc
with the acid, and by very simple mechanical arrangements, we can
give to the iron an upward and downward or a horizontal motion, thus
producing the conditions essential to the motion of any machinery.
This moving force is produced by the oxidation of the zinc; and,
setting aside the name given to the force in this case, we know that
it can be produced in another manner. If we burn the zinc under the
boiler of a steam-engine, consequently in the oxygen of the air
instead of the galvanic pile, we should produce steam, and by it a
certain amount of force. If we should assume, (which, however, is
not proved,) that the quantity of force is unequal in these
cases,--that, for instance, we had obtained double or triple the
amount in the galvanic pile, or that in this mode of generating
force less loss is sustained,--we must still recollect the
equivalents of zinc and coal, and make these elements of our
calculation. According to the experiments of Despretz, 6 pounds
weight of zinc, in combining with oxygen, develops no more heat than
1 pound of coal; consequently, under equal conditions, we can
produce six times the amount of force with a pound of coal as with a
pound of zinc. It is therefore obvious that it would be more
advantageous to employ coal instead of zinc, even if the latter
produced four times as much force in a galvanic pile, as an equal
weight of coal by its combustion under a boiler. Indeed it is highly
probable, that if we burn under the boiler of a steam-engine the
quantity of coal required for smelting the zinc from its ores, we
shall produce far more force than the whole of the zinc so obtained
could originate in any form of apparatus whatever.
Heat, electricity, and magnetism, have a similar relation to each
other as the chemical equivalents of coal, zinc, and oxygen. By a
certain measure of electricity we produce a corresponding proportion
of heat or of magnetic power; we obtain that electricity by chemical
affinity, which in one shape produces heat, in another electricity
or magnetism. A certain amount of affinity produces an equivalent of
electricity in the same manner as, on the other hand, we decompose
equivalents of chemical compounds by a definite measure of
electricity. The magnetic force of the pile is therefore limited to
the extent of the chemical affinity, and in the case before us is
obtained by the combination of the zinc and sulphuric acid. In the
combustion of coal, the heat results from, and is measured by, the
affinity of the oxygen of the atmosphere for that substance.
It is true that with a very small expense of zinc, we can make an
iron wire a magnet capable of sustaining a thousand pounds weight of
iron; let us not allow ourselves to be misled by this. Such a magnet
could not raise a single pound weight of iron two inches, and
therefore could not impart motion. The magnet acts like a rock,
which while at rest presses with a weight of a thousand pounds upon
a basis; it is like an inclosed lake, without an outlet and without
a fall. But it may be said, we have, by mechanical arrangements,
given it an outlet and a fall. True; and this must be regarded as a
great triumph of mechanics; and I believe it is susceptible of
further improvements, by which greater force may be obtained. But
with every conceivable advantage of mechanism, no one will dispute
that one pound of coal, under the boiler of a steam-engine, will
give motion to a mass several hundred times greater than a pound of
zinc in the galvanic pile.
Our experience of the employment of electro-magnetism as a motory
power is, however, too recent to enable us to foresee the ultimate
results of contrivances to apply it; and, therefore, those who have
devoted themselves to solve the problem of its application should
not be discouraged, inasmuch as it would undoubtedly be a most
important achievement to supersede the steam-engine, and thus escape
the danger of railroads, even at double their expense.
Professor Weber of Gottingen has thrown out a suggestion, that if a
contrivance could be devised to enable us to convert at will the
wheels of the steam-carriage into magnets, we should be enabled to
ascend and descend acclivities with great facility. This notion may
ultimately be, to a certain extent, realised.
The employment of the galvanic pile as a motory power, however,
must, like every other contrivance, depend upon the question of its
relative economy: probably some time hence it may so far succeed as
to be adopted in certain favourable localities; it may stand in the
same relation to steam power as the manufacture of beet sugar bears
to that of cane, or as the production of gas from oils and resins to
that from mineral coal.
The history of beet-root sugar affords us an excellent illustration
of the effect of prices upon commercial productions. This branch of
industry seems at length, as to its processes, to be perfected. The
most beautiful white sugar is now manufactured from the beet-root,
in the place of the treacle-like sugar, having the taste of the
root, which was first obtained; and instead of 3 or 4 per cent., the
proportion obtained by Achard, double or even treble that amount is
now produced. And notwithstanding the perfection of the manufacture,
it is probable it will ere long be in most places entirely
discontinued. In the years 1824 to 1827, the prices of agricultural
produce were much lower than at present, while the price of sugar
was the same. At that time one malter [1] of wheat was 10s., and one
klafter [2] of wood 18s., and land was falling in price. Thus, food
and fuel were cheap, and the demand for sugar unlimited; it was,
therefore, advantageous to grow beet-root, and to dispose of the
produce of land as sugar. All these circumstances are now different.
A malter of wheat costs 18s.; a klafter of wood, 30s. to 36s. Wages
have risen, but not in proportion, whilst the price of colonial
sugar has fallen. Within the limits of the German commercial league,
as, for instance, at Frankfort-on-the-Maine, a pound of the whitest
and best loaf sugar is 7d.; the import duty is 31/d., or 30s. per
cwt., leaving 31/d. as the price of the sugar. In the year 1827,
then, one malter of wheat was equal to 40 lbs. weight of sugar,
whilst at present that quantity of wheat is worth 70 lbs. of sugar.
If indeed fuel were the same in price as formerly, and 70 lbs. of
sugar could be obtained from the same quantity of the root as then
yielded 40 lbs., it might still be advantageously produced; but the
amount, if now obtained by the most approved methods of extraction,
falls far short of this; and as fuel is double the price, and labour
dearer, it follows that, at present, it is far more advantageous to
cultivate wheat and to purchase sugar.
There are, however, other elements which must enter into our
calculations; but these serve to confirm our conclusion that the
manufacture of beet-root sugar as a commercial speculation must
cease. The leaves and residue of the root, after the juice was
expressed, were used as food for cattle, and their value naturally
increased with the price of grain. By the process formerly pursued,
75 lbs. weight of juice were obtained from 100 lbs. of beet-root,
and gave 5 lbs. of sugar. The method of Schutzenbach, which was
eagerly adopted by the manufacturers, produced from the same
quantity of root 8 lbs. of sugar; but it was attended with more
expense to produce, and the loss of the residue as food for cattle.
The increased expense in this process arises from the larger
quantity of fuel required to evaporate the water; for instead of
merely evaporating the juice, the dry residue is treated with water,
and we require fuel sufficient to evaporate 106 lbs. of fluid
instead of 75 lbs., and the residue is only fit for manure. The
additional 3 lbs. of sugar are purchased at the expense of much
fuel, and the loss of the residue as an article of food.
If the valley of the Rhine possessed mines of diamonds as rich as
those of Golconda, Visiapoor, or the Brazils, they would probably
not be worth the working: at those places the cost of extraction is
28s. to 30s. the carat. With us it amounts to three or four times as
much--to more, in fact, than diamonds are worth in the market. The
sand of the Rhine contains gold; and in the Grand Duchy of Baden
many persons are occupied in gold-washing when wages are low; but as
soon as they rise, this employment ceases. The manufacture of sugar
from beet-root, in the like manner, twelve to fourteen years ago
offered advantages which are now lost: instead, therefore, of
maintaining it at a great sacrifice, it would be more reasonable,
more in accordance with true natural economy, to cultivate other and
more valuable productions, and with them purchase sugar. Not only
would the state be the gainer, but every member of the community.
This argument does not apply, perhaps, to France and Bohemia, where
the prices of fuel and of colonial sugar are very different to those
in Germany.
The manufacture of gas for lighting, from coal, resin, and oils,
stands with us on the same barren ground.
The price of the materials from which gas is manufactured in England
bears a direct proportion to the price of corn: there the cost of
tallow and oil is twice as great as in Germany, but iron and coal
are two-thirds cheaper; and even in England the manufacture of gas
is only advantageous when the other products of the distillation of
coal, the coke, &c., can be sold.
It would certainly be esteemed one of the greatest discoveries of
the age if any one could succeed in condensing coal gas into a
white, dry, solid, odourless substance, portable, and capable of
being placed upon a candlestick, or burned in a lamp. Wax, tallow,
and oil, are combustible gases in a solid or fluid form, which offer
many advantages for lighting, not possessed by gas: they furnish, in
well-constructed lamps, as much light, without requiring the
expensive apparatus necessary for the combustion of gas, and they
are generally more economical. In large towns, or such establishments
as hotels, where coke is in demand, and where losses in stolen tallow
or oil must be considered, together with the labour of snuffing
candles and cleaning lamps, the higher price of gas is compensated.
In places where gas can be manufactured from resin, oil of turpentine,
and other cheap oils, as at Frankfort, this is advantageous so long
as it is pursued on small scale only. If large towns were lighted in
the same manner, the materials would rise in price: the whole amount
at present produced would scarcely suffice for two such towns as
Berlin and Munich. But no just calculation can be made from the
present prices of turpentine, resin, &c., which are not produced
upon any large scale.
[Footnote 1: Malter--a measure containing several bushels, but
varying in different countries.]
[Footnote 2: Klafter--a cord, a stack, measuring six feet every
way.]
LETTER V
My dear Sir,
Until very recently it was supposed that the physical qualities of
bodies, i.e. hardness, colour, density, transparency, &c., and still
more their chemical properties, must depend upon the nature of their
elements, or upon their composition. It was tacitly received as a
principle, that two bodies containing the same elements in the same
proportion, must of necessity possess the same properties. We could
not imagine an exact identity of composition giving rise to two
bodies entirely different in their sensible appearance and chemical
relations. The most ingenious philosophers entertained the opinion
that chemical combination is an inter-penetration of the particles
of different kinds of matter, and that all matter is susceptible of
infinite division. This has proved to be altogether a mistake. If
matter were infinitely divisible in this sense, its particles must
be imponderable, and a million of such molecules could not weigh
more than an infinitely small one. But the particles of that
imponderable matter, which, striking upon the retina, give us the
sensation of light, are not in a mathematical sense infinitely
small.
Inter-penetration of elements in the production of a chemical
compound, supposes two distinct bodies, A and B, to occupy one and
the same space at the same time. If this were so, different
properties could not consist with an equal and identical
composition.
That hypothesis, however, has shared the fate of innumerable
imaginative explanations of natural phenomena, in which our
predecessors indulged. They have now no advocate. The force of
truth, dependent upon observation, is irresistible. A great many
substances have been discovered amongst organic bodies, composed of
the same elements in the same relative proportions, and yet
exhibiting physical and chemical properties perfectly distinct one
from another. To such substances the term Isomeric (from 1/ao1/
equal and aei1/o1/ part) is applied. A great class of bodies, known
as the volatile oils, oil of turpentine, essence of lemons, oil of
balsam of copaiba, oil of rosemary, oil of juniper, and many others,
differing widely from each other in their odour, in their medicinal
effects, in their boiling point, in their specific gravity, &c., are
exactly identical in composition,--they contain the same elements,
carbon and hydrogen, in the same proportions.
How admirably simple does the chemistry of organic nature present
itself to us from this point of view! An extraordinary variety of
compound bodies produced with equal weights of two elements! and how
wide their dissimilarity! The crystallised part of the oil of roses,
the delicious fragrance of which is so well known, a solid at
ordinary temperatures, although readily volatile, is a compound body
containing exactly the same elements, and in the same proportions,
as the gas we employ for lighting our streets; and, in short, the
same elements, in the same relative quantities, are found in a dozen
other compounds, all differing essentially in their physical and
chemical properties.
These remarkable truths, so highly important in their applications,
were not received and admitted as sufficiently established, without
abundant proofs. Many examples have long been known where the
analysis of two different bodies gave the same composition; but such
cases were regarded as doubtful: at any rate, they were isolated
observations, homeless in the realms of science: until, at length,
examples were discovered of two or more bodies whose absolute
identity of composition, with totally distinct properties, could be
demonstrated in a more obvious and conclusive manner than by mere
analysis; that is, they can be converted and reconverted into each
other without addition and without subtraction.
In cyanuric acid, hydrated cyanic acid, and cyamelide, we have three
such isomeric compounds.
Cyanuric acid is crystalline, soluble in water, and capable of
forming salts with metallic oxides.
Hydrated cyanic acid is a volatile and highly blistering fluid,
which cannot be brought into contact with water without being
instantaneously decomposed.
Cyamelide is a white substance very like porcelain, absolutely
insoluble in water.
Now if we place the first,--cyanuric acid,--in a vessel hermetically
sealed, and apply a high degree of heat, it is converted by its
influence into hydrated cyanic acid; and, then, if this is kept for
some time at the common temperature, it passes into cyamelide, no
other element being present. And, again inversely, cyamelide can be
converted into cyanuric acid and hydrated cyanic acid.
We have three other bodies which pass through similar changes, in
aldehyde, metaldehyde, and etaldehyde; and, again two, in urea and
cyanuret of ammonia. Further, 100 parts of aldehyde hydrated butyric
acid and acetic ether contain the same elements in the same
proportion. Thus one substance may be converted into another without
addition or subtraction, and without the participation of any
foreign bodies in the change.
The doctrine that matter is not infinitely divisible, but on the
contrary, consists of atoms incapable of further division, alone
furnishes us with a satisfactory explanation of these phenomena. In
chemical combinations, the ultimate atoms of bodies do not penetrate
each other, they are only arranged side by side in a certain order,
and the properties of the compound depend entirely upon this order.
If they are made to change their place--their mode of arrangement--by
an impulse from without, they combine again in a different manner,
and another compound is formed with totally different properties. We
may suppose that one atom combines with one atom of another element
to form a compound atom, while in other bodies two and two, four and
four, eight and eight, are united; so that in all such compounds the
amount per cent. of the elements is absolutely equal; and yet their
physical and chemical properties must be totally different, the
constitution of each atom being peculiar, in one body consisting of
two, in another of four, in a third of eight, and in a fourth of
sixteen simple atoms.
The discovery of these facts immediately led to many most beautiful
and interesting results; they furnished us with a satisfactory
explanation of observations which were before veiled in mystery,--a
key to many of Nature's most curious recesses.
Again; solid bodies, whether simple or compound, are capable of
existing in two states, which are known by the terms amorphous and
crystalline.
When matter is passing from a gaseous or liquid state slowly into a
solid, an incessant motion is observed, as if the molecules were
minute magnets; they are seen to repel each other in one direction,
and to attract and cohere together in another, and in the end become
arranged into a regular form, which under equal circumstances is
always the same for any given kind of matter; that is, crystals are
formed.
Time and freedom of motion for the particles of bodies are necessary
to the formation of crystals. If we force a fluid or a gas to become
suddenly solid, leaving no time for its particles to arrange
themselves, and cohere in that direction in which the cohesive
attraction is strongest, no crystals will be formed, but the
resulting solid will have a different colour, a different degree of
hardness and cohesion, and will refract light differently; in one
word, will be amorphous. Thus we have cinnabar as a red and a
jet-black substance; sulphur a fixed and brittle body, and soft,
semitransparent, and ductile; glass as a milk-white opaque
substance, so hard that it strikes fire with steel, and in its
ordinary and well-known state. These dissimilar states and
properties of the same body are occasioned in one case by a regular,
in the other by an irregular, arrangement of its atoms; one is
crystalline, the other amorphous.
Applying these facts to natural productions, we have reason to
believe that clay-slate, and many kinds of greywacke, are amorphous
feldspar, as transition limestone is amorphous marble, basalt and
lava mixtures of amorphous zeolite and augite. Anything that
influences the cohesion, must also in a certain degree alter the
properties of bodies. Carbonate of lime, if crystallised at ordinary
temperatures, possesses the crystalline form, hardness, and
refracting power of common spar; if crystallised at a higher
temperature, it has the form and properties of arragonite.
Finally, Isomorphism, or the equality of form of many chemical
compounds having a different composition, tends to prove that matter
consists of atoms the mere arrangement of which produces all the
properties of bodies. But when we find that a different arrangement
of the same elements gives rise to various physical and chemical
properties, and a similar arrangement of different elements produces
properties very much the same, may we not inquire whether some of
those bodies which we regard as elements may not be merely
modifications of the same substance?--whether they are not the same
matter in a different state of arrangement? We know in fact the
existence of iron in two states, so dissimilar, that in the one, it
is to the electric chain like platinum, and in the other it is like
zinc; so that powerful galvanic machines have been constructed of
this one metal.
Among the elements are several instances of remarkable similarity of
properties. Thus there is a strong resemblance between platinum and
iridium; bromine and iodine; iron, manganese, and magnesium; cobalt
and nickel; phosphorus and arsenic; but this resemblance consists
mainly in their forming isomorphous compounds in which these
elements exist in the same relative proportion. These compounds are
similar, because the atoms of which they are composed are arranged
in the same manner. The converse of this is also true: nitrate of
strontia becomes quite dissimilar to its common state if a certain
proportion of water is taken into its composition.
If we suppose selenium to be merely modified sulphur, and phosphorus
modified arsenic, how does it happen, we must inquire, that
sulphuric acid and selenic acid, phosphoric and arsenic acid,
respectively form compounds which it is impossible to distinguish by
their form and solubility? Were these merely isomeric, they ought to
exhibit properties quite dissimilar!
We have not, I believe, at present the remotest ground to suppose
that any one of those substances which chemists regard as elements
can be converted into another. Such a conversion, indeed, would
presuppose that the element was composed of two or more ingredients,
and was in fact not an element; and until the decomposition of these
bodies is accomplished, and their constituents discovered, all
pretensions to such conversions deserve no notice.
Dr. Brown of Edinburgh thought he had converted iron into rhodium,
and carbon or paracyanogen into silicon. His paper upon this subject
was published in the Transactions of the Royal Society of Edinburgh,
and contained internal evidence, without a repetition of his
experiments, that he was totally unacquainted with the principles of
chemical analysis. But his experiments have been carefully repeated
by qualified persons, and they have completely proved his ignorance:
his rhodium is iron, and his silicon an impure incombustible coal.
LETTER VI
My dear Sir,
One of the most remarkable effects of the recent progress of science
is the alliance of chemistry with physiology, by which a new and
unexpected light has been thrown upon the vital processes of plants
and animals. We have now no longer any difficulty in understanding
the different actions of aliments, poisons, and remedial agents--we
have a clear conception of the causes of hunger, of the exact nature
of death; and we are not, as formerly, obliged to content ourselves
with a mere description of their symptoms. It is now ascertained
with positive certainty, that all the substances which constitute
the food of man must be divided into two great classes, one of which
serves for the nutrition and reproduction of the animal body, whilst
the other ministers to quite different purposes. Thus starch, gum,
sugar, beer, wine, spirits, &c., furnish no element capable of
entering into the composition of blood, muscular fibre, or any part
which is the seat of the vital principle. It must surely be
universally interesting to trace the great change our views have
undergone upon these subjects, as well as to become acquainted with
the researches from which our present knowledge is derived.