in medicine. A considerable portion of it is consumed by dyers, to give
brightness to some of their colours. It is also employed in the assay of
metals, to discover the presence of iron; and having the property of
rendering lead brittle, is sometimes used in the manufacture of shot. By
coppersmiths and tinners it is used for cleansing the surface of the
metals which they are about to cover with tin. In certain manufactories
sal─ammoniac is mixed with tobacco, to give that article, or the snuff
that is made from it, additional stimulant properties. Sal─ammoniac
dissolved in nitric acid (30) forms the fluid named _aqua─regia_, which
is employed in the solution of gold.
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ORDER II.—METALLIC SALTS.
SALTS OF IRON.
208. _GREEN VITRIOL, IRON VITRIOL, or COPPERAS, is a mineral salt formed
on a decomposition of pyrites (236) by the moisture of the atmosphere.
It is also called SULPHAT OF IRON._
_Its colour is bright green, and its taste very astringent; a solution
of it in water dropped on oak bark instantly produces a black spot._
Although copperas is occasionally found in grottoes, caverns, the
galleries of mines, and other places; yet, being much in request by
dyers, tanners, and the manufacturers of ink, it is artificially
prepared from pyrites. This mineral being moistened and exposed to the
air, a crust is formed upon it, which is afterwards dissolved in water;
and from this the crystals of vitriol are obtained by evaporation.
The principal use of vitriol is in dyeing woollen articles, hats, and
other manufactures, black. It is the basis of ink, and is used in the
manufacture of Prussian blue. If it be reduced to powder by the action
of fire in a crucible, and mixed with powder of galls, it forms a dry
portable ink. Sulphuric acid (24) may be obtained from this kind of
vitriol by distillation. The residue, after the process is completed, is
used as a red paint; and when washed, is employed for the polishing of
steel.
SALTS OF COPPER.
209. _BLUE VITRIOL, or SULPHAT OF COPPER, is a blue salt formed by a
combination of copper with sulphuric acid (24)._
This substance, though sometimes found in a state of concretion, or in
the form of powder disseminated over the surface of stones that have
been in contact with water impregnated with it, is more frequently an
artificial preparation obtained from evaporating the water which runs
through copper mines. In the mines of Neussol, in Hungary, at the depth
of 380 feet beneath the surface of the ground, are several vats, placed
at different distances, for the purpose of collecting the water
impregnated with copper, and which flows into them through a kind of
gallery above. From this water the vitriol is afterwards separated by
evaporation. A process somewhat similar is pursued in our own country.
In the principal blue vitriol manufactories established in France, the
operation is thus carried on. Pieces of copper are first dipped into
water, and their surface, while wet, is covered with a stratum of
powdered sulphur. The copper thus prepared is put into an oven, and
heated to redness. After some time, it is taken out, and, while hot, is
plunged into a vessel filled with water. These operations are repeated
several times, till the whole of the copper is dissolved, and the water
becomes loaded with vitriol. Thus saturated, the water is placed over a
fire till all the fluid particles are dissipated, and the vitriol alone
is left.
Blue vitriol is used by artists and manufacturers in various ways. It is
employed in dyeing: and enters into the composition of black colours, to
which it gives depth and solidity. Blue feathers are stained by plunging
them into a hot solution of it. The beautiful grass─green colour of the
shops, called _mineral green_, is made from blue vitriol; and
fowling─pieces and tea─urns are browned by washing them with a
preparation of it.
SALTS OF ZINC.
210. _WHITE VITRIOL, or SULPHAT OF ZINC, is a whitish, yellowish, or
greenish white salt, formed by a combination of zinc (241) with
sulphuric acid (24)._
Although the white vitriol that is used in commerce is chiefly an
artificial preparation, this salt sometimes occurs in a natural state,
in mineral repositories that contain blende (241); and it appears to be
formed by a decomposition of that ore. It is found at Holywell, in
Flintshire, and in some parts of Cornwall.
When white vitriol is artificially prepared, the blende is roasted, and
thrown, while red hot, into a vessel filled with water; in which it is
allowed to remain about eighteen hours. This process is repeated several
times; and, after the solution has become clear, it is removed into
leaden vessels, and the water is evaporated by means of heat. On
cooling, it crystallizes. After this the crystals are melted in a copper
vessel, and the surface of the solution is skimmed with a hair sieve. It
is then poured into a wooden vessel, and stirred till it becomes cool,
and acquires a sufficient degree of consistence, when it is formed into
loaves for sale. In this state it has the appearance and colour of
refined sugar. White vitriol is chiefly manufactured in Germany.
It is used in medicine; and is employed in great quantities by
varnishers, to make their oil varnishes dry more readily than they
otherwise would. A fine white colour, called _zinc─white_, which is more
durable than white lead, is prepared from it. Dyers use a considerable
quantity of white vitriol to render deeper the colours produced by
madder, cochineal, and other substances.
A pleasing experiment is made by mixing in a phial a small quantity of
solution of white vitriol with a little liquid ammonia. Though each of
the fluids is transparent when separate, yet the zinc will now be
immediately precipitated in a white mass; and, what is peculiarly
deserving of remark, if then shaken, it will almost as instantly be
re─dissolved.
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CLASS III.—COMBUSTIBLES.
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SULPHUR FAMILY.
211. _COMMON SULPHUR, or BRIMSTONE, is a yellow, dry, and brittle
substance, which, in burning, yields a suffocating fume: the smell of
this, under the denomination of_ sulphureous, _is well known._
_Sulphur is found in a pure or native state in nearly all volcanic
countries: it is about twice as heavy as water; and is sometimes
crystallized in the form of octohedrons, whose bases are rhombs. It
exists abundantly in a state of combination with several metallic
substances, and is also formed in putrid animal remains._
A great proportion of the sulphur which is used in commerce is obtained
by the process of roasting copper, and other ores, previously to their
being smelted. It passes off in the form of vapour, and, on being
received into chambers constructed for the purpose, is there deposited
in a powdery state. The substance thus formed is the _flour of sulphur_
of the shops. It is afterwards melted in large pans, and cast in wooden
tubes, to make the hard, or _roll brimstone_. Nearly all the sulphur
used in France comes from the Solfatara of Italy. This volcanic country
every where exhibits indications of the agency of subterraneous fires.
Nearly the whole ground is bare and white; and, in every part, is warmer
than the atmosphere during the greatest heat of summer. A sulphureous
vapour is constantly emitted from the earth, and sulphur is condensed in
various parts, and in great abundance. This is collected, packed in
casks, and exported to Marseilles, where it undergoes certain
preparations that are necessary towards purifying and rendering it fit
for sale.
A considerable quantity of sulphur is employed in the composition of
gunpowder (206). Its readiness of taking fire is the reason of its being
employed in the making of matches. Sulphur gives a blue colour to
artificial fire─works. Its vapour is used for the whitening of silk and
wool, and also for the bleaching of straw used for making ladies’ hats.
Modellers employ sulphur to make moulds for various kinds of casts; and
artists are enabled, by means of it, to take sharp and beautiful
impressions of medals and engraved stones. The mode of doing this is
very simple. The sulphur is put into an earthen vessel called a
crucible, and placed on a hot fire. It soon melts; and if kept some time
over the fire, becomes thick and dark─coloured. When poured into water
in this state, it is as soft as wax. It may now be easily worked between
the fingers into any given form: and, if pressed upon a seal or engraved
stone, will be found to retain a perfect impression of it. It is this
property of sulphur of which Mr. Tassie, of Leicester─fields, London,
has availed himself, to furnish extremely elegant impressions of many
antique gems.
Sulphur was much used by the ancients in medicine; and it is now
occasionally administered both as an external and internal remedy. The
compounds formed from it are employed to considerable extent in various
processes of dyeing and calico printing. Many of the mineral waters,
those, for instance, of Harrowgate (299) and Moffat (300), are indebted
to sulphur for their most valuable qualities.
This substance has the property of becoming electric by rubbing. On
exposure to a gentle heat, it melts; but if the heat be increased, it is
entirely consumed, and passes off in vapour. When ignited, and the
combustion is slow, it burns with a suffocating and acid fume, and blue
flame; but when the combustion is quick it burns with a white and vivid
flame. If exposed to a sudden, though gentle heat, by holding it, for
instance, in a hand when that is warm, it will sometimes break in pieces
with a crackling noise.
It is a remarkable circumstance, that, if a bar of iron be heated to
perfect whiteness, and then touched with a roll of sulphur, the two
bodies combine, and drop down together, in a fluid state, forming what
is called _sulphuret of iron_, a compound of the same nature as iron
pyrites (236). A piece of iron rolled out very thin may be apparently
melted in the hand, by putting it, when heated to whiteness, upon a
thick piece of solid sulphur. It is, however, necessary, that this
experiment be performed with great care; and under a chimney, or in a
place where there is a current of air, to carry off the suffocating
vapour.
Useful as sulphur is, in various ways, its most important application is
supposed to be for the production of _sulphuric acid_, or _spirit of
vitriol_ (24). One mode in which this acid is obtained for the purposes
of commerce, is by burning a mixture of sulphur and nitre (206) in large
chambers lined with lead. In this process the nitre supplies a
considerable portion of oxygen (21) to the sulphur, and the air of the
atmosphere furnishes the rest. Thus a substance which, in a natural
state, is one of the mildest that we are acquainted with, is by this
operation converted into a corrosive and dangerous, though useful fluid.
Its taste is strongly acid: and, when applied to animal or vegetable
substances, it soon corrodes, and destroys their texture.
The properties of sulphuric acid have rendered it extremely valuable for
numerous purposes, both in the arts and in the laboratory. It has been
long employed by chemists, as one of their most useful and frequent
agents.
The fluid that is put into the bottles for procuring _instantaneous
light_ is no other than sulphuric acid; and it is poured among filaments
of asbestos (which it will not corrode), for the same purpose as ink is
sometimes poured upon cotton. The matches are slips of wood dipped in a
mixture of equal weights of sugar or charcoal powder, and what the
chemists call hyperoxy─muriat of potash. These are to be rubbed together
in a mortar, but with great care, as by strong friction the mixture is
apt to explode. To obtain a light, nothing farther is requisite than to
dip a match, thus formed, into a bottle containing the acid.
BITUMEN FAMILY.
212. _NAPHTHA, or ROCK OIL, is a yellow or brownish bituminous fluid, of
strong penetrating odour, somewhat greasy to the touch, and so light as
to float even on spirit of wine._
_By exposure to the air, the consistence of naphtha is increased, and it
passes into petroleum (213)._
There are copious springs of naphtha at Baku, on the shore of the
Caspian Sea; and also in some parts of Italy, particularly at
Monte─Chiaro, near Piacenza. At Pitchford, in Shropshire, extensive
strata or beds of sandstone are saturated with this mineral fluid, which
is obtained from the stone by distillation, and is sold, as a remedy
against sprains and rheumatism, under the name of _Betton’s British
oil_.
By the Persians and Russians naphtha is used internally as a cordial. On
the shores of the Caspian it is burned in lamps, instead of oil; and, in
some parts of Italy it is employed in the lighting of churches and
streets. When mixed with certain vegetable oils, it forms an excellent
varnish.
It is the property of naphtha to take fire on the approach of a light,
and to burn with great readiness and a white flame, leaving scarcely any
residuum. The town of Broseley, in Shropshire, was formerly celebrated
for a _burning spring_, which was first discovered in the month of June,
1711. Its original issuing from the ground was announced by a terrible
noise in the night, which awakened several persons who lived near the
spot. Some of these, on going out to ascertain the cause of the alarm,
perceived, about two hundred yards from the river Severn, an
extraordinary shaking of the earth, and a little bubbling of water
through the grass. On digging round the spot, the water sprang up to a
great height, and a candle which one of them held in his hand, set it on
fire. This circumstance excited great curiosity; and many persons, from
different parts of the adjacent country, came to visit what was called
the “burning well.” To prevent this spring from being destroyed, an iron
cistern was placed upon it, with a small hole in the cover, through
which the water might be viewed. When a lighted candle was put into this
hole, the water immediately took fire, darting and flashing in a violent
manner, much in the same way as spirits do in a lamp, but with greater
agitation. It would sometimes burn for forty─eight hours successively,
and without any sensible diminution: and a tea─kettle, full of water, by
being placed upon the hole, has been made to boil in nine minutes. In
1747, this spring had been lost for many years; but another was shortly
afterwards discovered, the issuing of which was announced by a rumbling
noise under ground, similar to that which had been formerly heard. This,
however, also disappeared in the year 1756, by the sinking of a coal─pit
in the neighbourhood.
213. _PETROLEUM, or MINERAL OIL, is a fluid bitumen, of somewhat greater
consistency than naphtha: of black, brown, or sometimes dingy green
colour._
_By exposure to the air it assumes the consistence of tar, and is then
called MINERAL TAR (214)._
This substance exudes spontaneously from the earth, or from clefts of
rocks, and is found in nearly all countries, particularly in the East
Indies, Italy, France, Spain, Germany, and England. In the neighbourhood
of Rangoon, in Pegu, there are several hundred wells of petroleum. These
are of square form, of considerable depth, and each lined with cassia
wood staves. The oil is drawn from them pure, and in a liquid state, and
is conveyed thence in small jars. The whole annual produce of this
district is estimated at more than 400,000 hogsheads.
At Colebrook Dale, in Shropshire, there is a spring of petroleum. This
was discovered at the depth of about thirty yards beneath the surface of
the earth, in digging an archway for the conveying of coals from a very
deep pit. The petroleum was at first found to ooze from between the
crannies of the rock, but it soon afterwards poured forth in a
considerable stream. The utility of this fluid having been made known,
large iron pipes were formed from the spring into pits sunk for the
purpose of receiving it. From these pits it is conveyed into immense
caldrons, where it is boiled until it attains the consistency of pitch.
Since the first discovery of this substance, three different springs of
it have broken out. One of these is near the celebrated iron bridge; and
the fluid that issues from it is almost pellucid, but, at the same time,
is thicker than treacle.
Petroleum easily takes fire, and, in burning, yields a strong, sharp,
and somewhat unpleasant odour; and a thick and disagreeable smoke. In
cold weather it congeals in the open air.
In Pegu, and other parts of the East, petroleum is used in place of oil
for lamps. Boiled with a species of resin, it is employed for painting
the timber of houses, and covering the bottoms of boats and other
vessels. In the latter respect it is considered to be particularly
efficacious, by protecting the timber from the attacks of marine worms.
It is also used by the inhabitants of eastern countries as a lotion in
cutaneous eruptions, and as an embrocation in bruises and rheumatic
affections. The ancient Egyptians used it in the embalming of dead
bodies. In some countries lumps of earth are soaked with petroleum, and
are employed as fuel.
214. _MINERAL TAR, or BARBADOES TAR, is a fluid kind of bitumen,
somewhat thicker than petroleum, and nearly of the consistence of common
tar. It is viscid, of a black, brownish black, or reddish colour._
_In burning its smell is disagreeable, but less pungent than that of
most other kinds of bitumen. Its weight is somewhat greater than that of
water._
In the West Indies, where this substance is principally found, it is
applied to many of the purposes for which the preceding species is used;
but its principal repute has been obtained from its being thought useful
in disorders of the breast and lungs, though this application of it is
considered very improper. It is likewise used as an external remedy in
paralytic disorders.
215. _ELASTIC BITUMEN, or MINERAL CAOUT─CHOUC, has a strong resemblance
to Indian rubber. In some instances it is elastic, and so soft as to
adhere to the fingers, and in others brittle, and so hard as nearly to
resemble asphalt (216)._
_Its colour is yellowish, reddish brown, or blackish. One kind of this
mineral, when fresh cut, nearly resembles fine cork, both in texture and
colour._
This extraordinary substance, which will expunge the marks of black lead
in the same manner as Indian rubber, was first discovered, about the
year 1786, in cavities of the lead mine of Odin, near Castleton, in
Derbyshire, and it has not hitherto been found elsewhere. Elastic
bitumen appears to be a peculiar modification of petroleum, in its
passage to asphalt: and probably owes its elasticity to its cellular
texture, and to the moisture with which it is combined.
216. _ASPHALT, or SOLID BITUMEN, is a brittle substance, of black or
brownish black colour, and of consistence somewhat harder than pitch._
_It has nearly the same weight as water, is smooth to the touch, does
not stain the fingers, and has little or no smell unless it be rubbed or
heated. When heated, it melts, swells and inflames; and, if pure, burns
without leaving any ashes._
The ancients were well acquainted with this substance, which is nothing
more than mineral tar (214) in an indurated or hardened state. It is
found on the surface of volcanic productions, and floats, in solid
pieces, and in considerable abundance, on the Asphaltic Lake, in Syria,
which has thence received its name. This lake is also called the Dead
Sea, from a notion that the odour arising from the asphalt destroys even
birds which fly over it: Maundrell, however, states that this is not
true, as he saw several birds fly about and over it, without
experiencing the slightest injury.
Asphalt is also found near ancient Babylon; and there is reason to
suppose that the mortar so celebrated amongst the ancients, and with
which the walls of Babylon and of the Temple of Solomon were cemented,
was nothing more than a preparation of asphalt. We are informed by
Herodotus that a composition of heated bitumen, mixed with the tops of
reeds, was used by the ancients as a cement. This account is confirmed
by modern travellers, who assert that the remains of buildings have been
discovered in which bitumen was formerly thus employed. It is presumed
to be the same substance which, in our translation of the Old Testament,
is called pitch, and which was used by Noah, as an exterior and interior
coating of the ark; by the mother of Moses as a coating for the little
vessel in which he was exposed; and on various other occasions.
As an article of modern utility, it is to be remarked that the Arabians
dissolve asphalt in oil, and, with the mixture, smear their horse
harness, to preserve it from the effects of weather, and the attacks of
insects. In a state of solution it is applied, in several eastern
countries, as a covering for timber and the bottoms of ships. It is
occasionally used in the cleansing and healing of ulcers, and other
sores. In France it is manufactured into a substance which is in
considerable request for greasing the wheels of carriages. It is used by
the makers of watch─dials, who mix it with lamp black, and oil of
turpentine; but its chief use is as an ingredient in certain varnishes,
and particularly in the varnish used by copper─plate engravers. It is
frequently adulterated by a mixture with common pitch; but this is
easily discovered by the smell.
Besides the countries and places already mentioned, asphalt is found in
several parts of America, in the island of Trinidad, in the province of
Neufchatel, and many parts of the Continent of Europe.
COAL FAMILY.
217. The component parts of coals are principally carbon or charcoal
(48), and bitumen (216).
Some kinds of coal are laminar, and others compact. They in general burn
freely, with a bituminous odour, and leave a considerable residuum.
This invaluable mineral is found in beds, or strata, frequently betwixt
clay slate (257) and sandstone (267), and seldom betwixt those of
limestone (140). It chiefly occurs in the northern hemisphere,
particularly in countries which lie nearly in the same latitudes with
Great Britain; in Siberia, Germany, Sweden, France, Canada, and
Newfoundland; and in some of the northern parts of China. It is stated
to be abundant in New Holland; but we have no distinct account of coal
in the continent of Africa. No fewer than seventy different kinds of
coals are brought to the London market, the value and prices of which
greatly differ. Of these the coals called _Wall’s─end_, from the name of
the pit, near Newcastle, whence they are obtained, usually bear the
highest price.
218. _COMMON COAL, or PIT COAL, is of black colour, and has generally a
slaty structure and foliated texture._
_When handled it stains the fingers; and when burnt it cakes more or
less during combustion. Its component parts are usually charcoal (48)
and bitumen (216), with a small portion of clay, and sometimes with
pyrites, or sulphat of iron (236). What is called slaty coal contains a
greater portion of clay than other kinds._
Some foreign writers have ascribed the great wealth possessed by this
country to the coals which are here produced in such abundance, and
which facilitate, in a very essential degree, nearly all its
manufactures, and consequently are a means of promoting its commerce to
an extent which is possessed by few other countries. All our great
manufacturing towns, Birmingham, Sheffield, Leeds, Glasgow, &c. are
situated either in the midst of coal districts, or in places to which
coals are conveyed, with little expense, by canal carriage.