_white iron_, of which saucepans, boilers, drinking vessels, and other
utensils of domestic economy are made, consists only of thin iron plate
coated with tin. It is thus formed. The iron plates are immersed in
water rendered slightly acid by spirit of salt (muriatic acid, 202) or
spirit of vitriol (sulphuric acid, 211): after which, to clean them
completely, they are scoured quite bright. These plates are then each
dipped into a vessel filled with melted tin, the surface of which is
covered with suet, pitch, or resin, to prevent the formation of dross
upon it. The tin not only covers the surface of the iron, but completely
penetrates it, giving to its whole substance a white colour.
In a manner similar to this, stirrups, buckles, bridle─bits, and other
articles, are tinned.
Iron is usually tinned before, but copper always after it has been
formed into utensils. The object to be attained by the tinning of copper
is to prevent the vessels made of that metal from being corroded, and to
preserve the food prepared in them from being mixed with any particles
of that poisonous substance called verdigris, which is formed by such
corrosion. In the tinning of copper vessels, their interior surface is
first scraped very clean with an iron instrument, and then rubbed over
with sal─ammoniac (207), for the purpose of more completely cleansing
them, and also of preventing the formation of verdigris from the copper
during the operation. The vessel is then heated, and a little pitch is
thrown into it. While quite hot, a piece of tin is applied to the
copper, and this, instantly uniting with it, soon clothes the whole
surface with tin.
This metal, when amalgamated with mercury, is used for the silvering of
looking─glasses (228). When tin is melted in an open vessel, its surface
is soon found to be covered with a grey powder, which is an oxide (21)
of the metal, and is generally called _dross_. If the heat be continued,
the colour of this powder becomes yellow. In this state it is known by
the name of _tin─putty_, and is employed in polishing glass, steel, and
other hard substances. When the heat is very violent, the metal takes
fire, and is converted into a fine white oxide, which is used to render
glass opaque, for the forming of enamel. Oxide of tin is also an
important article to dyers. It is employed by them, in large quantities,
to give brightness to such colours as are used in forming scarlets and
other reds: and to precipitate the colouring matter of other dyes.
Tin is an essential ingredient in _bell─metal_, _bronze_, _pewter_, and
various other compounds. It may be combined with lead, in any
proportion, by fusion; and this alloy is harder, and possesses much more
tenacity than tin. The hardest alloy is a composition of three parts of
tin and one of lead. The presence of the tin destroys, in a great
measure, the noxious qualities of the lead. It is sometimes customary to
tin copper vessels with this mixture, and it has been ascertained that
such vessels are in no respects injurious.
There are three kinds of _pewter_ in common use. These are called
_plate_, _trifle_, and _ley pewter_. The first, which is made into
plates and dishes, is formed of tin, with a small proportion of lead and
antimony (245). The second, or _trifle pewter_, which is made in
somewhat different proportions, is used for the quart and pint pots of
the publicans: and the _ley pewter_, which is formed of three parts of
tin and one of lead, is manufactured into wine and spirit measures.
Tin may be beaten into leaves or plates that are much thinner than
paper. But, when it is thus worked, several leaves must be joined
together. They then support each other, and yield to the hammer without
tearing. These leaves are used for the silvering of glass globes, and
the plating of other metals. Those that are used for the silvering of
looking─glasses are much thicker. The article called _tin─foil_ is an
alloy, consisting generally of two parts of tin and one of lead; and
capable of being beaten to less than the thousandth part of an inch in
thickness.
239. _LEAD is a heavy metal, of pale and livid grey colour when broken,
not sonorous when pure, very flexible, and so soft that it may be marked
with the nail. It stains paper or the fingers of a bluish colour, and is
about eleven times heavier than water._
T_he most common state in which lead is found is in combination with
sulphur and a small portion of silver. This ore is known by the name of_
galena, _and is frequently in the form of blackish cubical crystals.
Lead is also found in union with arsenic (242) and many acids._
Great Britain possesses the most important lead─mines in the world; and
those that are best known are in the counties of Flint and Derby. The
latter are supposed to have been worked even in the time of the Romans.
Lead mines are entered sometimes by perpendicular shafts, and sometimes
(when in the sides of hills) by levels. In some of the Derbyshire mines,
where the depth of the veins will admit of it, the men work, at
different heights, of from four to six feet above each other, along what
are called stoops; the uppermost men being two or three yards before
those next in succession, and thus forming a kind of steps. The
implements used are picks, hammers, and strong iron wedges; and the
rocks are also frequently loosened by means of gunpowder.
When the ore is brought out of the mine, it is sorted and washed, to
free it from dirt and rubbish. After this it is spread on a board; the
best pieces are picked out and separated; and those containing ore mixed
with spar (194) or other substances, are placed separate, to be broken,
and again picked. After the ore, by pickings and washing, has been
sufficiently cleansed from extraneous matters, it is roasted in a kind
of kiln to free it from the sulphur that is combined with it. The next
process is to mix it with a certain quantity of coke, charcoal, or peat,
and submit it to the smelting furnace. In this furnace there are
tap─holes, which, when the lead is melted, are opened, and the metal, in
a fluid state, runs into a large iron pan. The dross which floats on its
surface is now skimmed off; and the metal is taken out by ladles, and
poured into cast iron moulds, with round ends. The lead thus formed, is
ready for use, and has the name of _pig lead_. According to their size,
the pieces that are thus cast have the appellation of _pigs_, and
_half─pigs_.
Lead is mentioned in the Sacred Writings; and is described by Homer as
in common use at the period of the Trojan war. The ancients seem to have
considered it as nearly allied to tin. The Romans employed it to sheathe
the bottoms of their ships, fastening it to the planks and timbers by
nails made of bronze.
When first melted, lead is bright, but it soon tarnishes by exposure to
the air. It melts at a temperature very low in comparison with most
other metals; and when a strong heat is applied, it boils and
evaporates.
Lead is much employed in the useful arts. When rolled between iron
cylinders to a requisite state of thinness and uniformity, it is used
for the covering of houses and churches, notwithstanding the danger, in
case of fire, to persons within, who are exposed to a shower of burning
metal. It is cast into pipes, cisterns, and reservoirs for water, as
well as into large boilers for chemical purposes. But all culinary or
domestic vessels made of lead, particularly if intended for the keeping
of acid liquors, should carefully be avoided, as the surface of the lead
is thereby corroded, and the liquid contained in them is rendered
poisonous. Hence arises that dreadful complaint, too well known where
cyder is kept in leaden cisterns, called the _Devonshire colic_; hence
also the injury which sometimes follows from the use of lead in the
glazing of coarse earthenware.
Great quantities of lead are consumed for the making of _shot_. For this
purpose the metal is alloyed with arsenic (242), to render it more
brittle; and to render the grains more round and perfect than they
otherwise would be. Shot is formed by dropping the melted alloy into
water, through an iron or copper frame, perforated with round holes,
according to the size required. For the smallest shot the elevation is
about ten feet above the water; and for the largest about a hundred and
fifty feet.
An alloy of lead and tin, in the proportion of two parts of lead and one
of tin, forms the _solder_ which is used by plumbers. The _types_ that
are used by printers for very large characters are sometimes composed of
an alloy of lead and copper. Lead is also used, with tin, in the
manufacture of _pewter_.
_Oxides of Lead._
The different oxides (21) of lead are easily soluble in oil, and
consequently are of great use to painters. Of these the following are
the most important:
_White Lead_, or _Ceruse_.—This is made by suspending thin plates of
lead over heated vinegar, in such manner that the vapour which rises
from the acid may circulate about the plates. By this process the plates
become at length entirely corroded, and converted into a heavy white
powder. The manufacture of white lead is a most unhealthy trade, and is
confined to a few persons, who have large conveniences for the purpose.
This substance, when mixed with oil, is used as a paint for wood─work
both of the outsides and insides of buildings. The fumes that are
emitted from white paint are extremely noxious. Persons who breathe them
are frequently seized with pains, and experience symptoms not much
unlike those that precede palsy; and the danger which attends the
inhabiting of apartments recently painted is well known. The odour of
vinegar will correct the pernicious effect of these exhalations, by
acting as a solvent, and combining with, and precipitating them. We are
informed that white lead, dangerous as it is, was in great request among
the Roman ladies as a cosmetic. It is sometimes used as an external
application for ulcers and other kinds of sores.
_Massicot_ is a mineral substance of yellow colour, used for painting,
and prepared from the dross or pellicle that is formed by the melting of
lead.
_Red Lead_, or _Minium_, is a mineral substance of red colour, used for
painting, and made, by a tedious and troublesome process, from massicot.
For this purpose the massicot is ground to a fine powder, put into a
furnace, and constantly stirred, whilst the flame of the burning coals
plays against its surface for about forty─eight hours, when it is
converted into a red powder, which is the article under consideration.
It is subsequently passed through very fine iron sieves. The use of red
lead as a pigment is well known; but as it is liable to turn black,
vermilion is generally preferred to it. It is sometimes employed in
medicine as an external application for abating inflammations, for
cleansing and healing ulcers, and the like; and is used in the
manufacture of glass.
_Litharge_ is another kind of oxide of lead. This is prepared by
exposing calcined lead to a brisk fire for a certain length of time. The
substance, on cooling, concretes into a flaky matter. Litharge is used
by potters for the glazing of earthenware, but vessels that are glazed
with it are thereby rendered unwholesome. It is also employed, in the
composition of the finer kinds of glass, for the purpose, not only of
giving them greater transparency, but also of rendering them capable of
sustaining sudden changes from heat to cold, and of giving to them a
susceptibility of being cut without breaking. It, however, adds
considerably to the weight of the glass.
_Litharge Plaster_, or _Diachylon Plaster_, as it is more frequently
called, is prepared by boiling two pints of olive oil with one pint of
litharge, adding water, and constantly stirring the mixture till they
are duly incorporated. This plaster is applied in excoriations of the
skin, slight wounds, and other sores.
_Sugar of Lead_ is a preparation either from the metal itself, or from
white lead and distilled vinegar. It is usually observed in the form of
small slender crystals, which have a glossy appearance like satin. This
substance is employed, in considerable quantity, by dyers and calico
printers; and is the basis of a liquid frequently used in medicine,
called _Goulard_, or _Goulard’s Extract_. Although in itself a most
virulent poison, it is often used by unprincipled dealers for correcting
the rancidity of oil of almonds and olive oil; and a similar pernicious
fraud is practised by dissolving a portion of it in wines which are
becoming acid, in order to correct their acidity. These frauds, however,
are easily detected by preparations or tests, which are sold by chemists
for that purpose. Perhaps the best and simplest test is Harrowgate
water: a little of this poured into the suspected compound will discover
the presence of lead by giving to the fluid a dark brown or blackish
tinge.
The following is a pleasing experiment. Dissolve an ounce of sugar of
lead in about a quart of water; filter the solution through a piece of
blotting paper, and put it into a glass decanter, suspending in it a
piece of zinc by a brass wire. A decomposition will take place; the lead
will be set at liberty, and will attach itself to the zinc, forming
there a sort of metallic tree.
* * * * *
It has been stated that silver is usually a component part of lead ore.
To disengage this, where the quantity is sufficient to repay the
expense, the lead, after it has been smelted, is subjected to the action
of what is called a refining furnace. A continued blast of fresh air is
thrown upon its surface by means of large bellows, while the lead is
kept in a state as intensely hot as possible. This by degrees converts
the lead into a yellow scaly oxide or dross. The oxide, thus formed, is
driven off from the melted metal as it rises, and the silver is left
alone at the bottom, in a metallic state. After the operation is
complete, the oxide is fused with charcoal, and again reduced to
metallic lead.
* * * * *
We must not omit to mention that, in some of the mines of Derbyshire,
there is a singular variety of lead ore called _slickenside_. This is a
kind of galena, which presents, to the eye, a smooth and bright surface,
appearing as if it were plated. Sometimes it forms the sides of
cavities; and it has the extraordinary property, when merely pierced
with the miner’s tool, of rending with great violence, and exploding
with a crackling noise. Some miners, fearless of danger, venture to
scratch it with their tools; and, on coming again to the spot, they
often find that, during their absence, the slickenside has exploded, and
fallen off in considerable quantity. Sometimes, however, they suffer for
their imprudence. Mr. Mawe, in his account of the Mineralogy of
Derbyshire, says, that he has seen a man come out of a mine cut
violently, as if he had been stabbed about the neck and in other parts
of the body, in consequence of the explosion of slickenside which he had
pierced. The cause of this extraordinary phenomenon has not been
explained.
240. _NICKEL, when pure, is a fine white metal, somewhat resembling
silver in appearance, but it is attracted by the magnet, and has itself
the property of attracting iron._
_It is ductile and malleable, difficult of fusion, and about nine times
heavier than water. This metal is always mixed with arsenic (242) and
iron._
Nickel is found in Cornwall, and in some other counties of England; in
Germany, Sweden, France, Spain, and several parts of Asia. The Chinese
employ it in making white copper; and, in conjunction with copper and
zinc, they manufacture it into various kinds of children’s toys. Nickel
gives a certain degree of whiteness to iron. It is used, with advantage,
by some of the Birmingham manufacturers, in combination with that metal,
and by others in combination with brass. If it were possible to discover
an easy method of working nickel, there can be little doubt but it would
be found a very valuable metal for surgical instruments, for compass
needles, and other articles, as it is not, like iron, liable to rust.
When nickel is freely suspended, it points to the north and south, in
precisely the same manner as the common magnetic needle.
Oxide of nickel is used for giving colours to enamels and porcelain. In
different mixtures it produces brown, red, and grass─green tints.
241. _ZINC, or SPELTER, as it is sometimes called, is a bluish white
metal formed in thin plates adhering together. It has a very perceptible
taste, is about seven times heavier than water, rather harder than
silver; and possesses but a small degree of malleability and ductility,
except under certain circumstances._
_This metal is never found in a pure state; and the principal ores from
which it is procured are known by the names of_ Calamine _and_ Blende.
_Of these the former is an oxide (21) of zinc combined with carbonic
acid (26), and the latter is a combination of zinc with sulphuric acid
(24)._
The ores of zinc are very abundant in many countries. We are informed
that nearly the whole of Flintshire in North Wales abounds with
calamine; and that, so entirely ignorant were the inhabitants of its
use, as, till after the middle of the eighteenth century, to have even
mended their roads with it. These roads, however, have since been turned
up in many places, and the materials have been converted to more
valuable purposes. Derbyshire affords a great quantity of the ores of
zinc, particularly calamine. This is found at various depths, generally
in beds of yellow, or reddish brown clay, and usually near some vein of
lead ore.
The mode of extracting zinc from its ore is by distillation. The process
adopted, in some parts of Saxony, is equally simple and ingenious. An
inclined stone is placed near the anterior part of a furnace, in which
the ore of lead containing zinc is fused. A great part of the zinc
condenses upon this stone, and flows, in drops or globules, into a
quantity of charcoal placed at the bottom to receive it. These globules
are afterwards again melted, to run the metal into a mass.
When exposed to the air, the surface of zinc is soon tarnished, but it
scarcely undergoes any other change. It has a certain degree of
ductility. When heated a little above 218° of Fahrenheit, it is
malleable; and, when annealed, may be passed through rollers, and formed
into thin sheets or leaves. Although, previously to being thus heated,
it is brittle; on now cooling, it continues soft, flexible, and ductile.
The inconvenience arising from the brittleness of the zinc being
removed, this metal is applicable to many useful purposes. It may even
be drawn into wire, but the tenacity of this is not great: a piece of
zinc wire, one tenth of an inch in diameter, will sustain only a weight
of twenty─six pounds without breaking. It has been proposed to
substitute zinc in the place of tin for the lining of copper vessels;
but it has not hitherto been ascertained whether this can be done with
effect, and without injury. Prizes have of late been offered, to a
considerable extent, in France, for the ascertainment of this fact. In
China, zinc is employed as a current coin of the country; and for this
purpose it is used in the utmost purity. The Chinese also, as well as
the artists of our own country, employ it to a great extent in various
alloys. It is used in the manufacture of _brass_, _pinchbeck_ or
_prince’s metal_, and _bronze_, all of which consist of this metal in
combination with different proportions of copper (230). _Tutenag_ is a
well known white metal, made principally of zinc, and used for forming
candlesticks and other articles. When tutenag is well manufactured, it
is of good colour, and not more disposed to tarnish than silver. Zinc is
one of the metals employed to form the galvanic or voltaic apparatus;
and its filings are mixed with gunpowder, to produce those brilliant
stars and spangles which are seen in the best kinds of artificial
fire─works. Preparations of zinc are occasionally used in medicine. If a
thin plate of zinc be applied to the upper surface of the tongue, and a
shilling to the lower surface, and both metals, after a little while, be
brought into contact, a very peculiar taste will, at that instant, be
perceived. The same sensation will be perceived, though in a weaker
degree, if the silver be placed at the top and the zinc at the bottom.
If a silver probe be introduced high up one of the nostrils, and be
brought into contact with a piece of zinc placed on the tongue, a
sensation not unlike that of a strong flash of light will be produced in
the corresponding eye. A similar perception will result, both at the
moment of contact and that of separation, if one of the metals be
applied as high as possible between the gums and upper lip, and the
other in a similar situation with the under lip, or even under the
tongue.
A white oxide (21) prepared from zinc, was, some years ago, proposed as
a substitute for white lead in house painting. This oxide is not
dangerous in its application; and does not become yellow when mixed with
oil. But these advantages are counterbalanced by some defects, which
have hitherto caused it to be rejected. It is lighter than white lead:
does not cover the surface so equally, nor so well; and is of
considerably higher price.
CALAMINE.—The principal use of calamine is in the manufacture of brass
(230); and the mines of Derbyshire, and of Limbourg in the Netherlands,
supply with this mineral nearly all the brass works in Europe. After the
calamine is dug out of ground, it is reduced to pieces not in general
larger than a nut. It is then roasted for five or six hours, in what is
called a reverberating furnace. The large pieces are separated, and the
small ones are passed through a sieve. It is washed; and, when dry, is
ground in a mill. In this state it is sold. The principal demand for it
is at Birmingham, for the different brass founderies in that town.
The use of calamine in the composition of brass was known at a very
early period. It is mentioned by Aristotle, who also makes a distinction
between the compound resulting from the mixture of copper and calamine
or brass, and that resulting from the mixture of copper and tin or
bronze.
────────────────────────────────────────────────────────────────────────
ORDER II.—BRITTLE METALS,
OR SUCH AS ARE NOT CAPABLE OF BEING FLATTENED OR ELONGATED BY THE HAMMER
WITHOUT TEARING OR BREAKING.
242. ARSENIC, _in a metallic state, has a bluish white colour, and
considerable brilliancy; it is remarkably brittle, is the softest of all
known metals, and is somewhat more than eight times heavier than water._
_It is found nearly pure, and in considerable abundance, in different
parts of Germany; usually occurring in masses of various shapes, and in
combination with a small portion of iron, gold, or silver._
_The arsenic sold in the shops, and too well known for its poisonous
qualities, is an oxide (21) of this metal artificially prepared._
In some mines on the Continent arsenic is very abundant, and is found
extremely injurious to the workmen. Being very volatile, its fumes
affect and destroy the lungs, and occasion death in a short time to many
of them. One of its ores, _arsenical pyrites_, is found abundantly in
Cornwall and Devonshire, accompanying ores of copper and tin; and, in
combination with other metals, it occurs, in a greater or less
proportion, in almost all mines.
Arsenic is occasionally used in the arts. It is employed in various
metallic combinations where a white colour is required, and,
particularly, for the whitening or bleaching of copper, which is thereby
also rendered capable of taking a fine polish; hence its use in many of
the compositions for the mirrors of reflecting telescopes, and for other
optical instruments. The manufacturers of glass frequently employ the
oxides of arsenic in the fabrication of that article. Arsenic is used in
the processes of dyeing and calico printing; and for the imparting of
different artificial shades and colours to furs. It is also used in the
manufacture of small shot, from its rendering the lead more brittle, and
better capable of being formed into grains, than it would be without
such admixture.
The arsenic of commerce is prepared to a great extent in Bohemia and
Saxony, by roasting cobalt ores for the manufacture of zaffre (247).
_White arsenic_ is made, by mixing the common oxide with potash, and
submitting it to a certain degree of heat, in vessels adapted to the
purpose; the arsenic, rising in fumes, is separated, leaving the sulphur
behind, united to the potash. This process is called sublimation.