by no means so hard. It is, however, capable of being cut and polished
as a gem, and is manufactured into various kinds of trinkets, which of
late years have been much in request for necklaces, brooches, and
bracelets. It is also cut into slabs, and mounted into snuff─boxes. Such
is the size of which it is sometimes found, that M. Patrin saw, at
Petersburgh, a plate of malachite thirty─two inches long and seventeen
inches broad, which was valued at 20,000 livres; but the finest
specimens in Europe are some slabs that are adapted as the tops of
tables, sideboards, &c. at Trianon, in the Park of Versailles: the
largest of these are nearly four feet in length and two feet wide. They
may indeed have been formed by various pieces joined together; but, if
so, the joints are so completely concealed as not to be discoverable
even by the closest examination. Malachite is sometimes employed for the
engraving of cameos, but is seldom cut in intaglio. Smaller pieces of
this substance, that are used for trinkets, are about the same value as
carnelian. Independently of its use, in the above respects, and also as
an ore of copper, malachite, when pure, is ground into powder, and
employed as a green pigment.
The Vosges Mountains in Lorraine, and certain copper mines of Saxony,
are celebrated for producing very fine specimens of malachite. This
beautiful mineral is also found in our own country, in the copper mines
of Cornwall and Wales.
_232. TURQUOISE. The beautiful light blue substances that are called
turquoises have usually been considered as the bones or teeth of
animals, impregnated with blue oxide (21) of copper; but they are
sometimes found in nodules which are certainly not of an osseous
nature._
Turquoises are frequently set in rings, necklaces, brooches, and other
female ornaments. In Persia they are very common; and, amongst the
Turks, are held in such estimation that persons of rank almost
constantly wear them in some part of their dress, as ring─stones, and to
adorn the handles of stilettoes. They are imported into England from
Russia, stuck with pitch upon the ends of straws; because if mixed
together in parcels, the purchaser would not easily be able, in turning
them over, to observe their colour, and ascertain their value.
In the turquoise there is nothing that can recommend it to notice except
the agreeable softness of its colour, which is particularly
distinguishable by candle─light; this alone has rendered it so
fashionable as an ornament in female dress, for rings, ear─drops, and
brooches, that the demand for it is at present greater than the supply.
Imitations of turquoise are easily made in paste, and not unfrequently
imposed upon the ignorant purchaser; but in these, though the colour is
correctly given, there is a glassy lustre much higher than that of the
real stone.
Of late years a spurious kind of turquoise has also found its way into
Europe, which is much softer than the genuine kind; has more of a green
than a blue cast, and is by no means capable of so good a polish.
233. _IRON is a well─known metal, of livid greyish colour, hard and
elastic, and capable of receiving a high polish. Its weight is nearly
eight times as great as that of water._
_It is seldom found in a truly native state, but occurs, abundantly, in
almost every country of the world, in a state of oxide (21), and
mineralized with sulphuric (24), carbonic (26), and other acids._
_Iron is found in plants, in several kinds of coloured stones, and even
in the blood of animals._
Of all the metals there are none which, in the whole, are so useful, or
are so copiously and variously dispersed as iron. Its uses were
ascertained at a very early period of the world. Moses speaks of
furnaces for iron, and of the ores from which it was extracted, and
tells us that swords, knives, axes, and instruments for cutting stones,
were, in his time, all made of this metal.
The most considerable iron mines at present existing are those in Great
Britain and France. After iron ore is dug out of the earth, it is
crushed or broken into small pieces, by machinery. It is next washed, to
detach the grosser particles of earth which adhere to it. This operation
ended, it is roasted in kilns, formed for the purpose, by which the
sulphur, and some other substances that are capable of being separated
by heat, are detached. It is then thrown into a furnace, mixed with a
certain portion of limestone and charcoal, to be melted. Near the bottom
of the furnace there is a tap─hole, through which the liquid metal is
discharged into furrows made in a bed of sand. The larger masses, or
those which flow into the main furrow, are called _sows_; the smaller
ones are denominated _pigs_ of iron; and the general name of the metal
in this state is _cast iron_.
With us iron is employed in three states, of cast iron, wrought iron,
and steel.
_Cast iron_ is distinguishable, by its properties of being, in general,
so hard as to resist both the hammer and the file; being extremely
brittle, and for the most part, of a dark grey or blackish colour.
A great number of useful and important articles are formed of cast iron,
such as grates, chimney backs, pots, boilers, pipes, and cannon shot.
These are made by casting ladles full of the liquid metal into moulds
that are shaped, for the purpose, in sifted sand.
_Wrought iron._ The process of converting cast iron into wrought or
malleable iron, is called _blooming_. The cast iron is thrown into the
furnace, and kept melted by the flame of combustibles which is made to
play upon its surface. Here it is suffered to continue for about two
hours, a workman constantly stirring it, until, notwithstanding the
continuance of the heat, it gradually acquires consistency, and
congeals. It is then taken out, while hot, and violently beaten with a
large hammer worked by machinery. In this state it is formed into bars
for sale.
The value of iron is beyond all estimate, and infinitely greater than
even that of gold. By means of this metal the earth has been cultivated
and subdued. Without it houses, cities, and ships, could not have been
built; and few arts could have been practised. It forms also the
machinery by which the most useful and important mechanical powers are
generated and applied.
_Steel_ is usually made by a process called _cementation_. This consists
in keeping bars of iron in contact with powdered charcoal, during a
state of ignition, for several hours, in earthen troughs, or crucibles,
the mouths of which are stopped up with clay. Steel, if heated to
redness, and suffered to cool slowly, becomes soft; but if plunged,
whilst hot, into cold water, it acquires extreme hardness. It may be
rendered so hard as even to scratch glass; and at the same time, it
becomes more brittle and elastic than it was before. Although thus
hardened, it may have its softness and ductility restored, by being
again heated, and suffered to cool slowly. A piece of polished steel, in
heating, assumes first a straw─yellow colour, then a lighter yellow,
next becomes purple, then violet, then red, next deep blue, and at last
of all bright blue. At this period it becomes red hot, the colours
disappear, and metallic scales are formed upon, and encrust its surface.
All these different shades of colour indicate the different tempers that
the steel acquires by the increase of heat, from that which renders it
proper for files, to that which fits it for the manufacture of watch
springs. Mr. Stoddart has availed himself of this property to give to
surgical, and other cutting instruments, those degrees of temper which
their various uses require.
The kind of steel which has been most celebrated in this country is that
imported from Syria under the name of _Damascus steel_. Germany is also
noted for its steel. The best steel manufactured in Britain is known by
the name of _cast steel_; and the making of it, although it was long
kept a profound secret, is now discovered to be a simple process. It
consists merely in fusing it with carbonat of lime (140), or in what is
called cementation, with charcoal powder, in a peculiar kind of furnace.
The iron produced in Sweden is considered superior to that of any other
country in Europe for the manufacture of steel.
All kinds of edge tools, where excellence is required, are made of
steel; and a steel instrument may be immediately known from an iron one,
by letting fall upon it a drop of nitric acid or aqua fortis (206),
somewhat diluted with water. If it be steel, this will occasion a black
spot; but if it be iron, it will not have this effect. Steel is
attracted by the magnet, and is capable of receiving a permanent
_magnetic property_, which has led to the discovery of the mariner’s
compass. Had iron been productive of no other advantages to mankind than
this, it would on this account alone have been entitled to their
greatest attention.
Iron, when exposed to the moisture of the atmosphere, becomes gradually
covered with a brown, or yellowish substance, known by the name of
_rust_, which, if suffered to continue without interruption, will
corrode the entire substance of the iron. The rust or oxide of iron (21)
is a substance in considerable request by calico printers for a dye.
_Iron─moulds_ are spots on linen occasioned by its exposure to iron in
damp situations; these are removeable only by the application of an
acid.
There are various modes of _preserving iron and steel_ from rust. The
following is recommended by an eminent French chemist as one of the
best. Mix copal varnish, made greasy with oil, with about four─fifths of
the best spirit of turpentine. Apply this by means of a sponge, over the
whole surface, and allow it to dry. This varnish may be successfully
used for all the metals; and particularly for the preservation of such
philosophical instruments as, by being brought into contact with water,
are liable to lose their splendour, and become tarnished.
234. _METEORIC STONES are a species of iron ore, which have at different
times been known to fall from the atmosphere._
_They have been seen only in shapeless masses, of from a few ounces to
several hundred pounds in weight. Their texture is granular. They are
covered externally with a thin blackish crust, and are, internally, of
an ashy grey colour, mixed with shining minute particles._
There is sufficient evidence to show that solid masses of stone have
been observed to fall from the air at a period considerably anterior to
the Christian era. Notwithstanding this, so very extraordinary was the
phenomenon, that, until the year 1802, it was generally regarded by
philosophers as a vulgar error. Mr. Howard, in that year, submitted to
the Royal Society a paper which contained an accurate examination of the
testimonies connected with events of this kind; and described a minute
analysis of several of the substances which had been said to have fallen
in different parts of the globe. The result of his examination was that
all these stony bodies differ completely from every other known stone;
that they all resemble each other, and are all composed of the same
ingredients.
The greatest number of the stones which have fallen from the air have
been preceded by the appearance of luminous bodies or meteors. These
meteors have burst with an explosion, and then the shower of stones has
fallen to the earth. Sometimes the stones have continued luminous until
they sunk into the earth, but most commonly their luminousness
disappeared at the time of the explosion. Their motion through the air
is surprisingly rapid, in a direction nearly horizontal; but they seem
to approach the earth before they explode. In their flight they have
frequently been heard to yield a loud whizzing sound. They are hot when
they first reach the earth; and exhibit, on their surface, visible marks
of fusion.
A general tradition has prevailed in almost all ages, and amongst all
people, of the fall of solid bodies from the atmosphere, under various
denominations, but, with us, more particularly, under that of
_thunderbolts_. In barbarous and uncivilized countries, these have
usually been ascribed to the miraculous judgment of the deity; and they
may be considered as the true origin of the worship of stones. The image
of Diana, mentioned in the Acts of the Apostles, as believed by the
Ephesians to have fallen down from Jupiter, and the Palladium or sacred
statue of Minerva, which also is said to have fallen from Heaven, and to
have been preserved in Troy, as a treasure, on the safety of which that
of the city depended, had each, no doubt, this origin. The Psalmist
evidently alludes to the falling of meteoric stones, when, speaking of
the Almighty, he says, “He made darkness his secret place; his pavilion
round about him with dark water, and thick clouds to cover him. At the
brightness of his presence his clouds removed; hailstones and coals of
fire. The Lord also thundered out of Heaven, and the Highest gave his
thunder; hailstones and coals of fire.”
Among numerous other instances of these stones, it is recorded that, on
the seventh of November, 1492, betwixt eleven and twelve o’clock at
noon, a dreadful clap of thunder was heard at Ensisheim, a considerable
town in Alsace, and that a huge stone was seen to fall on a field lately
sown with wheat. On several of the neighbours going to the place, the
hole it had formed was found to be about three feet in depth, and the
stone when dug out, weighed two hundred and sixty pounds. It was
preserved in the cathedral of Ensisheim until the beginning of the
French Revolution, when it was conveyed to the public library at Colmar.
There are in the British Museum two small pieces of this stone, and
fragments of several other meteoric stones which have fallen in
different parts of the world.
Two stones fell near Verona in Italy, in the year 1672, one of which
weighed three hundred, and the other two hundred pounds.
Mr. Sowerby, the publisher of English Botany, and of several other
highly estimable works, possessed a meteoric stone which fell near Wold
Newton in Yorkshire, in the afternoon of the thirteenth of December,
1795, and weighed fifty─six pounds. Whilst this stone was in motion
through the air, several persons perceived a body passing along the
clouds, although they were unable to ascertain what it was. It passed
over several different villages, and was also accurately and distinctly
heard. The day was foggy; and, though there was some thunder and
lightning at a distance, it was not until the stone fell that an
explosion took place which alarmed all the adjacent country; and
created, distinctly, a sensation that something very extraordinary had
happened. A shepherd belonging to Captain Topham was within a hundred
and fifty yards of the place where it fell; George Sawden, a carpenter,
within sixty yards; and John Shepley, one of Captain Topham’s farming
servants, was so near that he was forcibly struck by some of the mud and
earth that were raised by the stone dashing into the ground. In its fall
the stone excavated a place nineteen inches in depth (seven inches of
which were in a solid rock of chalk), and somewhat more than three feet
in diameter, fixing itself so firmly that some labour was required to
dig it out.
Another stone of considerable size fell in Scotland on the fifth of
April, 1704. A misty commotion was observed in the atmosphere, and,
nearly at the time of the stone falling, a report was heard as loud as
if three or four cannon had been fired at a little distance. The report
was succeeded by a violent rushing or whizzing noise; and, almost
immediately afterwards, the stone fell into a drain, in the presence of
two men and two boys, splashing the water to a distance of twenty feet
around. The stone, when dug out, was found to have sunk about eighteen
inches into the earth.
On the fifth of November, 1814, about half past four o’clock in the
afternoon, a dreadful peal of thunder was heard in the Doab in Persia,
and was immediately succeeded by a shower of large stones, many of them
from twenty─six to thirty pounds weight each. Several inhabitants of the
adjacent country were present at the time; and not fewer than nineteen
of the stones were collected.
Professor Pallas, many years ago, discovered lying on the surface of a
hill in Siberia, a mass of native iron, which weighed 1680 pounds. It
was considered by the natives as a holy relic, and was believed by them
to have fallen from heaven. M. de Bougainville, the French
circumnavigator, discovered, on the banks of the river La Plata, in
South America, an enormous mass of native iron, which he calculated to
have weighed about 100,000 pounds. And a mass of native iron, appearing
in every respect to have been of meteoric origin, was, some years ago,
discovered in the district of St. Jago del Estro, in South America. It
was in the middle of a great plain, and had no rock nor mountain near
it, and was calculated to have weighed about thirty tons.
The origin of meteoric stones is involved in great obscurity. Some
writers have imagined that they might be projected from distant
volcanoes; others, that they may have been detached from rocks, and had
their substance considerably changed by a concurrence of natural causes;
others, that they may have been generated in the air by a combination of
mineral substances; and others, that they may have been projected from
the moon. The latter was the opinion of La Place the astronomer, who
says that a mass, if thrown by a volcano from the moon, with a velocity
of about a mile and half per second, it will thence be projected beyond
the sphere of the moon’s attraction, and into the confines of that of
the earth; the consequence of which will be, that the mass must
presently fall to the earth, and become a part of it.
235. _LOADSTONE, or MAGNETIC IRONSTONE, is a compact blackish kind of
iron ore, which is possessed of the power of attracting iron, as well as
every substance which contains ferruginous particles. It is betwixt four
and five times as heavy as water._
This mineral is found in masses of different form and size in most of
the iron mines of Europe and America, and, when submitted to the
furnace, it yields a considerable proportion of metal. It makes
excellent bar iron, but very indifferent cast iron. In Sweden, and
particularly at Roslager, magnetic iron stone is found quite pure, and
the iron that is wrought from it is imported in considerable quantities
into Great Britain, for the purpose of being manufactured into steel.
The appellation of load, or leading stone, has been given to this kind
of iron from its magnetic virtues; for it is not only endowed with the
property of attracting iron, but also of pointing itself, and even
enabling a needle touched with it to point, towards the poles of the
world. We are, however, entirely ignorant what is the cause of this very
extraordinary property.
Artificial magnets, constructed of steel, not only possess all the
essential virtues of the genuine loadstone, but even in a much higher
degree. The natural magnet is consequently now little esteemed except as
an object of curiosity.
236. _PYRITES, or MARCASITE, is a mineral substance, formed by a
combination of iron with sulphur._
_It is usually of a bronze, yellow, or brownish colour, very various in
form, being massive, globular, club─shaped, oval, or crystallized; and
so hard as to strike fire with flint._
Few minerals are more common than this, as it occurs, in some state or
other, in almost every rock and vein. It is often found among coals;
and, when heated, decrepitates with a loud unpleasant noise and
sulphureous smell. To the decomposition of this mineral it is that the
hot temperature of almost all the mineral waters may be ascribed.
The name of pyrites, which in the Greek language signifies _firestone_,
has been obtained by this mineral from its property of striking sparks
from steel. It was formerly used for fire─arms, as we now use flints. In
commerce it is known by the name of marcasite. Some years ago it was
much used, particularly in France, for the making of buttons and
buckles; and was cut and polished, by lapidaries, for trinkets,
particularly for the rims and hands of watches, and various kinds of
female ornaments. If skilfully cut in the form of small rose diamonds,
although an opaque substance, it has somewhat the appearance of a
diamond. In the tombs of the Peruvian princes, with whom a considerable
portion of their valuables was always interred, there have been found
polished plates of marcasite, which appear to have served them as
mirrors.
This mineral is never worked as an ore of iron; and it is principally
valued on account of the sulphur which can be obtained from it by means
of heat; and the green vitriol, or copperas (208), which it affords by
exposure to the air.
Ignorant persons frequently mistake iron pyrites for gold; but it is
easily distinguished from that precious metal by its brittleness. It
breaks when hammered, whereas gold is malleable, or may be extended by
hammering: it also strikes fire with steel, which gold will not.
237. _RED OCHRE, REDDLE, or RED CHALK, is an iron ore of blood─red
colour, which is sometimes found in powder, and sometimes in a hardened
state. It has an earthy texture, and stains the fingers when handled._
The principal use of red chalk is for drawing: the coarser kinds are
employed by carpenters and other mechanics, and the finer kinds by
painters. For the latter purpose it should be free from grit, and not
too hard. In order to free it from imperfections, and render it better
for use, it is sometimes pounded, washed, mixed with gum, and cast into
moulds of convenient shape and size.
Under the name of reddle, this substance is much used for the marking of
sheep; and (when mixed with oil) for the painting of pales, gates, and
the wood─work of out─buildings.
Another kind of iron ore, or rather a compound of the ores of iron and
manganese, is called _umber_. This mineral, which is of a brown colour,
is found in beds in the island of Cyprus, and is used as a kind of paint
both in a raw state and burnt.
238. _TIN is a white metal, somewhat like silver in appearance, but is
considerably lighter, and makes a squeaking or crackling noise when
bent. It is very soft and ductile, and has but little elasticity._
_This metal is always found either in a state of oxide (21), or in
combination with sulphur and copper; and is about seven times as heavy
as water._
The principal tin mines which are known to us are those of Cornwall,
Devonshire, Germany; the island of Banca, and peninsula of Malacca, in
India; and Chili and Mexico in America. Of these the most celebrated are
the mines of Cornwall, which are known to have been worked before the
commencement of the Christian era. Diodorus Siculus, who wrote forty
years before the birth of Christ, gives an account of these mines, and
says that their produce was conveyed to Gaul, and thence to different
parts of Italy. This species of metal was used in the time of Moses, and
is mentioned in the writings of Homer.
Tin is found in veins, or beds, but chiefly in veins, running through
granite and other rocks. In some of the valleys and low grounds of
Cornwall, the tin ore is found in rounded grains and masses. In these
situations, small grains of gold are sometimes found with it. To
separate the tin from earthy and other matters with which it is
intermixed, streams of water are passed over them; and these deposits
have the name of _stream─works_.
When the tin ore has been dug from the earth, or has been collected at
these stream─works, it is thrown into heaps, and broken to pieces. After
this it is washed, and subsequently roasted in an intense heat, for the
purpose of dissipating some of the substances with which it is combined.
It is lastly melted in a furnace, and thereby reduced to a metallic
state. The metal is then poured into quadrangular moulds of stone, each
containing about 320 pounds weight. These have the denomination of
_block─tin_, and are stamped by officers of the Duke of Cornwall, with
the impression of a lion, the arms of that duchy. This is rendered a
necessary operation before the tin can be offered for sale; and on
stamping, it pays a duty of four shillings per hundred weight to the
Prince of Wales, as Duke of Cornwall, who thence derives a very
considerable income.