with a hammer on an anvil or flat iron, such as is used by laundresses,
explodes with a stunning and disagreeable report, and with such force as
to indent both the anvil and the hammer. Four or five grains are as much
of this powder as ought to be used for such experiments. Its force is
much greater than that of gunpowder, but does not extend so far. Hence
it is a substance which might be rendered of great use in the blasting
of rocks.
_Corrosive sublimate_ is an extremely poisonous preparation from
mercury. Among other uses, it is employed by dyers as a mordant to fix
their colours. From certain proportions of corrosive sublimate rubbed
together, until they are perfectly incorporated, is formed _calomel_; a
salt which, of late years, has been extensively and most usefully
employed in medicine.
A valuable red colour or pigment called _vermilion_, or _artificial
cinnabar_, which was as well known to the ancients as it is to the
moderns, is usually formed of three parts of mercury and one of sulphur,
melted together, heated to redness, and then sublimated out of contact
of the air. The manufacture of vermilion was long kept a secret by the
Dutch; and it is stated that, before the late war, nearly 50,000 pounds
weight of it were annually made, in three furnaces, by four workmen,
near Amsterdam. Native cinnabar is sometimes used for the same purpose;
but the artificial kind is preferred on account of the purity and
brightness of its colour.
229. _SILVER is a white, brilliant, sonorous, and ductile metal,
somewhat more than ten times heavier than water._
_It is found in different states. Of these the principal is denominated_
native silver, _from its being nearly in a state of purity. Native
silver sometimes occurs in small lumps, sometimes in a crystallized
form, and sometimes in leaves, threads, or wire. In many instances the
latter are so connected with each other as to resemble the branches of
trees, in which case the ore is called_ dendritic. _There are also
several_ ores of silver, _in which this metal is combined with lead,
antimony, arsenic, sulphur, and other substances._
The silver that is produced from the mines of Potosi, in South America,
is of the dendritic kind; and is considered by the Spaniards as the
purest that is known. A range of mountains near Potosi, about twenty
miles in circumference, is said to be perforated by more than 300
shafts, or openings of mines, and to produce, in the whole, from 30,000
to 40,000 dollars’ worth of ore per week. The annual produce of the
silver mines in America has been estimated at near 2,400,000_l._
sterling.
Silver is also found in several parts of Europe; and, some years ago,
there were mines of this metal, worked to a great extent, at Konigsberg
in Norway. These were discovered in 1623, and they were found so
profitable, that in 1751 forty─one shafts and twelve veins were wrought
there; and 3,500 officers, artificers, and labourers, were employed. The
perpendicular depth of the principal shaft was more than 750 feet.
Specimens of native silver are not uncommon from some of the
copper─mines of Cornwall; and, many years ago, a vein of silver ore was,
for a short time, wrought with considerable advantage in the parish of
Alva, Stirlingshire, Scotland. It is said that from 40,000_l._ to
50,000_l._ worth of silver was obtained from it before the repository
was exhausted. We are informed that a mass of capillary native silver
was found, in veins traversing the blue─coloured limestone of Isla, one
of the Western Islands of Scotland. Great quantities of silver are
extracted from lead. There was lately melted in one refining house in
London 50,000_l._ worth of this metal, from lead of the Beralston mines
in Devonshire.
Different methods are employed, in different countries, to extract
silver from its ore. In Mexico and Peru the mineral is pounded, roasted,
washed, and then mixed with mercury in vessels filled with water; a mill
being employed for the more perfectly agitating and mingling them. By
this process the silver combines with the mercury. The alloy thus
obtained, after undergoing some further processes, is submitted to the
action of heat, by which the mercury passes off in a state of vapour,
leaving the silver behind. The silver is then melted and cast into bars
or ingots. In other countries, after the earthy matters are cleared from
the silver ore by pounding and washing, the remainder is melted with
lead: which, by a subsequent process, is separated, and leaves the
silver alone and pure.
This metal ranks next in value to gold. Like gold, it is coined into
money, and is manufactured into various kinds of utensils, such as
goblets, vases, spoons, and dishes, which have the general appellation
of _silver plate_. For all these purposes it is alloyed with copper,
which does not affect its whiteness, and is not easily detected, unless
it be in too great proportion: the intention of this is to render it
harder than it would otherwise be, and thereby the better to adapt it to
receive fine and sharp impressions on being cast. Our _standard silver_
is composed of somewhat more than 12¼ parts of pure metal and one part
of copper; and the metal of this standard is used, both for silver
plate, and in the coinage. The mark or stamp which is given to it at
Goldsmiths’ Hall is similar to that which has been explained for
sterling gold.
After platina (226) and gold (227), silver is considered the most
unchangeable of all metals. The air does not easily act upon its surface
in such manner as to injure it; but, when long exposed to the
atmosphere, especially in frequented or smoky places, it acquires a
covering or rust of dark brown colour, which, on examination, is found
to be what chemists denominate _sulphuret of silver_. The fumes of
sulphur and other inflammable substances blacken silver. Various powders
have been contrived with a view to restore to plate its original lustre;
but these should be used with caution, as some of them are very
injurious.
Silver is nearly as ductile as gold. It may be beaten into leaves so
thin that a single grain in weight will cover a space of more than
fifty─one inches; and it may be drawn into wire much finer than a human
hair, indeed so fine that a single grain of silver has, in this form,
been extended nearly to the length of 400 feet. It is this wire gilded
that has the name of gold wire; and what is denominated _gold lace_
(227) is but flatted silver thread gilt, twisted round silk, and woven.
The _plating_ of copper with silver is a very useful operation, and is
thus performed. Plates of silver are bound with iron wire, upon small
ingots of copper. The quantity generally allowed is one ounce of silver
to twelve ounces of copper. The surface of the plate of silver is made
not quite so large as that of the copper; and upon the edges of the
copper, which are not covered by the silver, a little borax (204) is
put. By exposing the whole to a strong heat, the borax melts; and, in
melting, contributes to fuse that part of the silver to which it is
contiguous, and to attach it, in that state, to the copper. The ingot,
with its silver plate, is then rolled between steel rollers moved by
machinery, till it is of proper thickness. It is afterwards cut into
such sizes and to such shapes as may be required for use. An ounce of
silver is thus often rolled out into a surface of three square feet,
having its thickness, upon the copper, not more than the
three─thousandth part of an inch. Hence we ought not to be surprised at
the silver being soon worn from the sharp edges of plated goods. To
prevent this, it is customary, with the best articles, to have all the
edges, and the parts liable to be worn, formed, to a considerable
thickness, of silver.
What is called _French plate_ is made by heating copper, or more
frequently, brass, to a certain degree, then applying leaf─silver to the
surface, and strongly rubbing it with a burnisher. The durability of
this plating depends of course on the number of leaves which are applied
on a given surface. For ornaments that are not much used ten leaves may
be sufficient; but a hundred will not last long, if the metal be exposed
to frequent handling or washing.
Besides the above, there are various modes of _silvering_ metal
articles, or, as it is called, _washing_ them with silver. All these are
performed by different chemical preparations of this metal.
The article denominated _shell─silver_, used by painters, is prepared,
by carefully grinding silver─leaf, with a little honey or gum water upon
a slab, or in a mortar, and separating the honey or gum by means of
water. When this is washed away, the silver may be put on paper, or kept
in shells, for use. When it is to be used, it must again be diluted with
gum water.
The application of silver─leaf for the silvering of paper or wood is
similar to that of gold─leaf (227).
Silver, dissolved in aqua fortis (nitric acid, 30), yields crystals,
which, afterwards melted in crucibles, form that grey mass usually
called _lunar caustic_, and by chemists _nitrat of silver_. This
preparation is of considerable use in surgical cases, being employed to
keep down fungous or proud flesh, in wounds and ulcers, and also for the
consuming of warts, small wens, and other excrescences upon the skin. It
is likewise, though a most violent medicine, sometimes given internally,
but in very small doses, to persons subject to epileptic fits. The
liquid in which the silver is dissolved becomes excessively caustic. It
gives to the skin, the hair, and almost all animal substances, an
indelible black colour. Hence it is often used as a specific for dyeing
the human hair. No person, however, would employ it for this purpose,
who was acquainted with its injurious qualities, not only to the hair
itself, but also to the skin, if permitted to come in contact with it.
The article called _indelible_, or _permanent marking ink_, for marking
linen, and other wearing apparel, is formed by dissolving, in a glass
mortar, two drachms of nitrat of silver, in six drachms of pure water,
and then adding to them two drachms, by measure, of thick gum water.
This is the ink for writing on the linen.—In another vessel dissolve
half an ounce of salt of tartar, or of the subcarbonat of soda, of
commerce, in four ounces of water; and add to the solution half an
ounce, by measure, of thick gum water. This forms the preparatory
liquor. With this the linen is to be thoroughly wetted at the part
intended to be marked. The linen is to be dried, and then to be written
upon by a clean pen dipped in the marking ink. The letters will at first
be pale, but by exposure to light and heat, they will soon become black;
and be so permanently fixed, that no washing nor bleaching can efface
them.
The attention of the curious has of late been turned to a very
extraordinary compound called _fulminating silver_, which explodes
without heat, and with even the slightest degree of friction. Of this
compound little _fulminating balls_ have been made. These are globules
of thin glass, each somewhat larger than a pea, and containing a grain
or two of fulminating silver. After the silver is put in, it is secured
by a piece of soft paper, pasted over the ball, so as completely to
cover it. These balls explode by merely crushing them under the heel of
the shoe. What are called _fulminating bombs_ are similar balls, but of
the size of hazel nuts. No one should attempt to explode these by
crushing them with the shoe, as their explosive effect is so violent as
sometimes to prove injurious.
Fulminating silver requires the utmost care. It should never be put into
phials, nor should it be in any way handled so as to produce much
friction. It is the most dangerous preparation that is known. The mere
touch of a hard substance will sometimes explode it; and its very
preparation is so hazardous that this ought never to be attempted
without a mask upon the face with strong glass eyes.
The following are three pleasing experiments with preparations of
silver:
1. Mix or amalgamate together four parts of silver leaf with two parts
of mercury (228) and dissolve this in diluted aqua fortis. To the
solution add as much water as will be equal to thirty times the weight
of the metals employed. Pour a portion of the above mixture into a
phial, and place at the bottom a small piece of silver. After it has
stood awhile, little filaments of silver will be seen to shoot up from
it somewhat in the form of a shrub. This apparent vegetation is
popularly called the _tree of Diana_.
2. A production nearly similar may be obtained by adding a little
quicksilver to a solution of nitrat of silver in water.
3. Drop upon a clean plate of copper a small quantity of solution of
lunar caustic, or nitrat of silver. In a short time a metallic
vegetation will be perceptible, branching out in pleasing forms, and in
various directions.
230. _COPPER is a red or orange─coloured metal, about nine times heavier
than water. It is the most sonorous of all metals, and, except iron, the
most elastic._
_It is found under a great variety of forms, sometimes in masses of pure
metal, but, more frequently, in combination with other substances,
particularly sulphur._
There are valuable copper mines in every quarter of the world; and the
use of copper is probably of greater antiquity than that of any other
metal. It is mentioned in the Old Testament; and, at a very early
period, domestic utensils and instruments of war were made of bronze, or
a compound of copper and tin. Even during the Trojan war, as we learn
from Homer, the combatants had no other armour than what was made of
bronze. The Greek and Roman sculptors are said to have executed fine
works of art in porphyry, granite, and other hard minerals, by means of
copper instruments; whence historians have been induced to believe that
the ancients possessed the secret of rendering this metal as hard as
steel: some of them even imagined that they had the means of converting
it into steel.
Copper is very abundant in several parts of Great Britain, particularly
in the island of Anglesea. The copper mines of Anglesea are situated on
the top of a mountain, and form an enormous cavity more than five
hundred yards long, a hundred yards broad, and a hundred yards deep. The
ore is got from the mine by pickaxes, and blasting with gunpowder. It is
then broken with hammers into small pieces, an operation which is
chiefly performed by women and children. After this, it is piled into
kilns of great length, and each about six feet high; from the upper
parts of which flues are attached that communicate with what are called
sulphur chambers. The kilns are closely covered; and fires are lighted
in different parts, that the ore may undergo the process of roasting.
The whole mass gradually kindles, and the sulphur, which is combined
with the ore, is expelled in fumes, by the heat, and is conveyed,
through the flues, to the sulphur chamber. This process occupies from
three to ten months, according to the size of the kilns; and, during
that period, the sulphur chamber is cleared four or five times. When the
operation is complete, or the ore is freed from the sulphur, it is taken
to places denominated slacking pits. It is subsequently conveyed to the
smelting houses, where, by intense heat, the pure metal is drawn off in
a fluid state.
As the water, which passes through several parts of the Paris mine, is
strongly impregnated with sulphat of copper (209), or copper held in
solution by sulphuric acid (24), the proprietors turn the course of this
water through certain large and shallow pits, which they have formed for
the purpose, and in each of which they place a quantity of iron. A
decomposition here takes place: the iron is corroded, and, at length,
entirely dissolved, and the copper, in the form of a brown mud, falls to
the bottom. One ton weight of iron, thus immersed, will produce nearly
two tons of copper mud, each of which, when melted, will yield sixteen
hundred weight of metal. This mode of obtaining copper is said to have
been an accidental discovery from one of the workmen, several years ago,
having left a shovel in the water, which, when afterwards taken out,
appeared changed into copper.
The magnitude of the above mentioned copper works may readily be
conceived, when it is stated that the beds of ore are, in some places,
more than sixty feet in depth: that the proprietors employ more than
1000 workmen; and that they ship, from the adjacent port of Amlwch,
upwards of 20,000 tons of copper, annually.
There is at Ecton, in Staffordshire, a copper mine which is now worked
at the depth of 1416 feet below the surface of the ground. This is the
deepest mine in England.
The uses of copper are numerous and important. When rolled into sheets,
betwixt large iron cylinders, it is employed for the covering of houses,
sheathing the bottoms of ships, and other purposes. As a covering for
houses, copper is lighter than slate, but whether it be more durable has
not been yet ascertained. The coppering of ships tends to facilitate
their progress through the water, by presenting a smoother surface than
that of wood, and not permitting shell animals to fasten to it as they
do to wood. It likewise preserves the bottoms of the ships from being
punctured by marine worms; and consequently secures to them a longer
duration than they would otherwise have. Plates, or flat pieces of
copper, are used by artists for engraving pictures upon, either by
cutting them with a sharp steel instrument, or corroding them with aqua
fortis (206), in lines drawn by a needle through a thin coat of wax
spread upon their surface.
Copper is manufactured into various kinds of cooking utensils. Great
care, however, ought to be taken that acid liquors, or even water
intended for drinking, or to be mixed with food, be not suffered to
stand long in such vessels, otherwise they will dissolve so much of the
metal as to give them disagreeable and even poisonous qualities. Yet, it
is remarkable that, while acid liquors are kept boiling, they do not
seem to dissolve any of the metal. Hence it is that confectioners, by
skilful management, prepare the most acid syrups in copper vessels,
without their receiving any unpleasant taste or injurious quality from
the metal. All vessels formed of this metal which are employed in
cookery, ought to have their inner surface covered with a coat of tin
(238).
As copper does not, like iron, strike fire by collision, it has on this,
as well as on some other accounts, been substituted for iron in the
machinery which is employed in gunpowder mills. It is also made into
water pipes, and sometimes into sash frames. Under the hammer it is
capable of being beaten into thin leaves like gold. Copper wire is much
employed by bell─hangers and other artisans. The filings of this metal
are used for giving a green colour to some kinds of artificial
fire─works.
Several preparations of copper are employed in medicine, some of them
internally, and others externally; but most of the former are violently
emetic.
_Verdigris_ is a rust or oxide (21) of copper, usually prepared from
that metal by corroding it with vinegar. There is a large manufactory of
verdigris at Montpelier in France. The workmen place alternate strata of
copper plates and husks of grapes, the latter of which speedily become
acid and corrode the metal. The verdigris, thus formed, is scraped off
as it collects on the surface; it is afterwards dried, and put in bags
or casks for sale. A manufactory of verdigris has lately been
established at Deptford, near London.
A solution of this substance in distilled vinegar affords permanent
crystals, which are improperly called _distilled verdigris_, and are
made into a green paint. Verdigris is principally consumed by dyers in
combination with logwood, for striking a black colour. It is a virulent
poison.
Oxide of copper is employed for giving a beautiful green colour to
porcelain. It also imparts the same colour to glass, and hence is
frequently employed for the formation of artificial emeralds.
_Alloys of Copper._
Of all metals that are known, copper is the most susceptible of alloy.
The most frequent and useful of these alloys are made with copper and
zinc, in different proportions.
_Brass_ is an alloy composed of three parts of copper, and about a
fourth part of zinc (241). It is a beautiful, useful, and well─known
yellow metal. Not being so apt to tarnish and rust as copper, and being,
in other respects, better adapted for the purpose than that metal, it is
much used for clock─work, and for mathematical and astronomical
instruments. It is more ductile than either copper or iron, and hence is
peculiarly fitted to be made into wire, for the strings of musical
instruments, and other purposes. Sieves are woven with brass wire, after
the manner of cambric weaving, and of such extreme fineness that similar
ones could not possibly be made with copper wire. Brass wire, flatted
and gilded, is sometimes made into lace. The finest brass is
manufactured at Geneva. It unites great beauty of colour to a high
degree of ductility; and is used chiefly for escapement wheels, and
other nicer parts of watch─making. For work in which there is no
friction it is necessary to cover brass with a kind of varnish or
_laquer_, to improve its colour, and prevent it from being tarnished by
exposure to the atmosphere.
_Prince’s Metal_, or _Pinchbeck_, is an alloy containing three parts of
zinc (241), and four of copper. This metal has nearly the same colour as
gold, and was formerly much in use for the manufacture of ornamental
articles of different kinds.
_Dutch Gold_ is formed by the cementation of copper─plates with calamine
(241), hammered out into leaves. This article is chiefly manufactured in
Holland and Germany, and has about five times the thickness of gold
leaf.
_Bronze_, and _the metal of which cannons are made_, consist of from six
to twelve parts of tin (238) combined with 100 parts of copper. This
alloy is brittle, heavier than copper, and of a yellow colour. Before
the method of working iron was brought to perfection, it was used by the
ancients for the manufacture of sharp─pointed instruments; and it is
supposed to have been the _æs_ or brass of the Romans.
_Bell Metal_, or the metal of which bells are formed, is usually
composed of three parts of copper and one of tin. Its colour is greyish
white; and it is very hard, sonorous, and elastic.
Bronze and bell metal are not, however, always made of copper and tin
only. They frequently have other admixtures, consisting of lead, zinc,
or arsenic. Bell─makers sometimes abuse the vulgar credulity by
pretending that they add a certain quantity of silver to the alloy, for
the purpose of rendering the bells more melodious: but they are better
acquainted with their business than to employ so valuable a metal in the
operation.
_White Copper_ is an alloy composed of equal parts of copper and arsenic
(242). The metal produced by this mixture is of a whitish colour, but
with a coppery tinge. It is freed from the latter by being melted
several times; and, by this process, is at last rendered as white as
silver. White copper is very brittle; but, if the arsenic be evaporated
by heat, it resumes its ductility, and still preserves its white colour.
When the operation is well performed, it is easy, at the first glance,
to mistake white copper for silver; but the difference may immediately
be ascertained from the properties inherent to the two metals.
White copper is employed in the manufacture of many kinds of trinkets:
and of a great number of domestic utensils; such as tea─pots,
coffee─pots, and candle─sticks.
231. _MALACHITE is a solid green copper ore, the surface of which has
frequently a bubbled appearance, and the interior is marked with
numerous irregular zones, and layers of different shades of green. It is
somewhat more than three times as heavy as water, and is so soft as to
be easily scratched by a knife._