sand, it forms glass, and answers much better for this purpose than
potash. In conjunction with oil and lime, it is employed in the
manufacture of soap; and it is used as a substitute for soap in the
cleaning and bleaching of linen, flannels, and worsted goods. If a weak
solution of soda be poured into foul bottles, or casks in which wine has
long been kept, it will cleanse them. It may also be successfully used
for the cleansing of vessels in which milk has become acid. Saddles,
bridles, or boot─tops, may be effectually cleaned by means of this
liquor, and restored nearly to their original colour and appearance.
The art of _soap─boiling_ may easily be illustrated by the following
experiment. Take a piece of quick─lime, slake it gradually by sprinkling
on it a sufficient quantity of water. When it is completely slaked, add
to it about twenty times its weight of water. To this mixture add two
parts, by weight, of common subcarbonat of soda, previously dissolved in
a sufficient quantity of water. Boil the whole for about half an hour,
strain it through a cloth, and boil it till so much of the water is
evaporated that a phial that will contain an ounce of water will hold
one ounce, seven pennyweights and a half, of this ley. Then mix in an
earthenware pipkin or basin, one part of the ley, with two parts of
olive oil. Place the mixture in a gentle heat, capable only of making
the liquor simmer, and allow it to simmer, stirring the liquor
continually, with a wooden stick, till, by letting a few drops of it
fall on a plate, the soap will be found to coagulate, and the water
become speedily separated from it. After which, pour out the contents
into a cup, and suffer it to cool.—Soap may also be prepared without
heat. If one part of the ley be mixed with two parts of olive oil, in a
glass or stone ware vessel, and the mixture be stirred, from time to
time, with a wooden spoon or spatula, it will become thick, and white;
in seven or eight days afterwards the combination will be completed, and
a white and firm soap will be obtained.
_White soap_ is formed of ingredients similar to those that have just
been mentioned. _Yellow soap_ is made with tallow, resin, and soda. Soap
may be formed by boiling shreds of woollen cloth with ley till the whole
has acquired a certain consistence. This kind of soap has been made, and
applied with success, in several manufactories in France.—The
combination of oil and other ingredients with potash (205), instead of
soda, affords what is called _soft soap_.
201. _NATRON, or CARBONAT of SODA, is a salt which consists of soda
(200) in combination with carbonic acid (26). It is massive, of greyish
colour, soluble in water, and has a disagreeable alkaline taste._
This salt is found in Egypt, on the surface of the earth, and
particularly near the margins of certain lakes called natron lakes. In
the summer season the water of these lakes is evaporated by the heat of
the sun, leaving a bed of natron generally about two feet in thickness.
This is broken with wedges and hammers; and packed up for sale in the
European markets. The waters of some of the lakes contain both common
salt and natron; and these, on evaporation, crystallize in successive
beds. Natron is found in considerable quantity under the form of an
efflorescence, on the surface of the earth, in the plains of Debreczin
in Hungary. It is likewise found in small quantity in the ashes of most
vegetables, but particularly in those of _salsoda_ and _salicornia_.
The ancient Egyptians are said to have made great use of natron for the
preservation of dead bodies, by macerating them in it for several months
previously to their being embalmed. Large quantities of this salt are
sometimes imported into England, by the East India Company’s ships, from
China, and other parts of the East. It is employed in the manufacture of
soap, and for the washing of linen. Glass─makers mix it with sand for
the formation of glass. On the continent it is administered as a
medicine in complaints of the bowels and liver. The ancients sometimes
employed a mixture of natron for soaking their seed corn, under an
impression, that, when afterwards committed to the earth, it would
thereby be rendered more fertile.
202. _COMMON SALT, or MURIAT of SODA, though found in some countries in
a solid and massive state, is for the most part an artificial
preparation from sea─water, and from the water of salt lakes and brine
springs. It consists of soda (200) in combination with muriatic acid
(29)._
Few productions, either natural or artificial, are in so much request as
common salt. It is used by the inhabitants of nearly all countries, for
correcting the insipidity of food. When applied in small quantities, it
accelerates the putrid fermentation; and, in this case, is considered to
aid digestion, by promoting the decomposition of the aliments. In larger
quantity it has a contrary effect, and tends to preserve organic
substances from corruption. Salt is used for glazing the surface of
coarse earthenware; and is employed in several processes of dyeing.
When this substance is dug out of the earth it has the appellation of
_rock salt_: and immense masses of it are found in different countries
of the world. The most considerable, as well as the most celebrated
_salt mines_, with which we are acquainted, are those about five miles
from Cracow, in Poland; and it is supposed that they contain more salt
than would be sufficient to supply the wants of the whole world for
several thousand years. On descending to the bottom of these mines, a
stranger is astonished to find a kind of subterraneous republic,
consisting of many families, who have their own peculiar laws and
polity. Here are likewise public roads, and carriages, horses being
employed to draw the salt to the mouths of the mine, where it is taken
up by engines. The horses, when once they are down, never more see the
light of day; and many of the people seem buried alive in this immense
abyss. Some are born there, and never stir out; others, however, have
occasional opportunities of breathing the fresh air in the fields, and
enjoying the light of the sun. The subterraneous passages or galleries
are very spacious; and, in many of them, chapels are hewn out of the
salt. In these are set up crucifixes, and the images of saints, before
which lights are kept continually burning. In some parts of the mine
huge columns of salt are left standing to support the rock. Its windings
are so numerous and intricate, that workmen have frequently lost their
way: the lights they carried have been burned out, and they have
perished before they could be found. The salt is taken from these mines
in blocks so large as, sometimes, to measure nine feet in length, four
feet in width, and two or three feet in thickness. In the year 1780, the
greatest depth to which the workmen had penetrated was about 320 yards,
and the mass of salt was considered to be in some places more than 240
yards thick, and to extend at least three leagues.
Near the town of Cardona, about fifty miles northwest of Barcelona, in
Spain, there is a mountain of salt, without cleft or crevice, 500 feet
high, and nearly three miles in circumference. In the province of
Lahore, in Hindostan, travellers have described a mountain of the same
mineral, not inferior to this in magnitude; and the elevated regions of
Peru afford rock salt at the height of 7000 feet above the level of the
sea.
At Northwich and Nantwich, in the county of Chester, there are salt
mines of great depth and extent. These are frequently visited by
travellers, and are found amply to repay the trouble and inconvenience
of descending into them. There are two principal beds of this substance;
the upper one is about forty─two yards below the surface, and twenty─six
yards thick. This was originally discovered about a century and a half
ago, in searching for coal. The lower bed has already been examined to
the depth of forty yards, without coming to the bottom; and it is about
the centre of this bed that the purest salt has been discovered. The
average depth of the cavity, formed by the workmen along the vein of
salt in the different mines, is supposed to be about sixteen feet. In
some of the mines, where pillars six or eight yards square are left to
support the roof, the appearance of the cavity is singularly beautiful:
and the effect is greatly increased when the mine is illuminated by
numerous candles fixed to the side of the rock. The scene so formed
would almost seem to realize the notion of the magic palaces of Eastern
poets. Some of the mines are worked in aisles or streets. The methods
employed in working out the salt offer nothing worthy of notice. Larger
masses are separated from the body of the rock, by blasting with
gunpowder; and are afterwards broken down with pickaxes, hammers, and
other instruments. The present number of mines in the vicinity of
Northwich is eleven or twelve, from which there are raised, on an
average, 50,000 or 60,000 tons of salt per annum. The greater part of
this quantity is exported to Ireland and the Baltic; and the remainder
is employed in Cheshire, and the adjacent counties.
Salt is also made from _brine springs_ in Cheshire, Cumberland,
Staffordshire, and Worcestershire; but the kind most commonly used in
England is that which is made from sea water, and has the name of _sea
salt_. The mode of manufacturing it is very simple. The water is first
pumped into shallow reservoirs of earth, called salt pans, or salterns.
In these it remains exposed to the sun until a certain proportion of the
water is evaporated, so as to leave it about seven times stronger than
in its original state. It is then conducted by another pump into flat
iron pans, eight or nine feet square, and as many inches deep. These,
being placed over a hot fire, the liquor or brine is boiled until nearly
all the remaining particles of water have passed off by evaporation, and
nothing is left in the pans but salt. This is thrown together into
proper vessels, for a few days, to drain, after which it is fit for use.
In some countries the whole evaporation is performed by the heat of the
sun; and, in extreme northern climates, where the sun would not have
sufficient power for the operation, a very different process is adopted.
The water is suffered to freeze in the salterns, and that portion of it
which continues uncongealed is so strongly saturated that it requires
only a moderate heat to evaporate the remainder of the water, and to
crystallize the salt.
_Bay salt_ is that which is produced from the evaporation of sea─water
by the heat of the sun only.
The inhabitants of Cardona, in Spain, make of the rock salt in their
neighbourhood various transparent articles, which they vend at a cheap
rate. These, which consist of small altars, figures of saints, crosses,
chandeliers, salt─cellars, &c. are as clear as crystal, and, to
appearance, as lasting. They are chiefly purchased by strangers as
curiosities, and are distributed over various parts of Spain and the
south of France.
The decomposition of salt furnishes the _muriatic acid_ (29), or _spirit
of salt_ of commerce. This liquid, which is much used in the arts, and
is in great request by chemists, is prepared, for common purposes, by
mixing one part of common salt with seven or eight parts of clay, and
distilling the mixture; or by distilling common salt and spirit of
vitriol or sulphuric acid (24), and receiving the product into a vessel
containing water.
It has been discovered that muriatic acid, in a state of gas, is an
excellent means of correcting putrid exhalations. In the year 1773, the
cathedral church of Dijon was so much infected by the corruption of
bodies which had been interred within its walls, that it was entirely
deserted. The professor of Chemistry at Dijon having been applied to for
assistance, placed, on a few burning coals, in the middle of the church,
a glass vessel containing six pounds of common salt. Upon this he poured
two pounds of sulphuric acid (24), precipitately withdrew, and shut all
the doors. The gas soon filled the whole cathedral. After twelve hours
the doors were thrown open, and a current of air was made to pass
through to remove the gas, which had entirely destroyed every putrid
odour.
The following has been recommended as an eligible mode of fumigating
rooms for the prevention of infectious disorders. Take six drachms of
powdered nitre (206), and six drachms of sulphuric acid (spirit of
vitriol); and mix them in a tea─cup, by adding to the nitre one drachm
at a time of the oil. During the preparation the cup must be placed on a
piece of heated iron, and the mixture stirred with a tobacco pipe or
piece of glass. As soon as the fumes arise, the cup must be moved about
to different parts of the room or house that are to be fumigated.
203. _GLAUBER SALT, or SULPHAT of SODA, is a salt which consists of soda
(200) in combination with sulphuric acid (24). It occurs in an
efflorescent or powdery state, on the borders of salt lakes; or, more
commonly, in a state of solution, in certain mineral waters._
This salt, which was originally discovered by a German chemist whose
name was Glauber, has a nauseously bitter and saline taste. It is found,
in an efflorescent state, on meadow ground at Eger, in Bohemia; and on
the walls of old galleries in mines, at Grenoble, in France. It is also
abundant in the ashes of some kinds of vegetables, especially of sea
weeds. The waters of the Mediterranean yield a great proportion of it;
and the Glauber salt used for commercial purposes is chiefly prepared
from sea─water, or by decomposing common salt, in order to procure
muriatic acid (29). It may also be obtained by saturating soda with
sulphuric acid (24).
The use of this salt in medicine is well known; and, in some countries,
it is employed as a substitute for soda (200), in the manufacture of
white glass. It ought to be kept in well─corked bottles, as otherwise
the crystals soon fall into powder.
The following is a pleasing experiment, which shows a singular and
almost instantaneous crystallization of Glauber’s salt. Dissolve this
salt by adding portions of it gradually to water kept boiling until the
water will dissolve no more. Pour the solution, whilst boiling, into
common medicine phials previously warmed, and immediately cork them. Set
the phials in a quiet place without shaking them. The solution, when
cool, will remain perfectly fluid till the cork is taken out; but the
moment this is done, and the air is admitted, it will begin to
crystallize on its upper surface, in fine satin─like crystals, which
will shoot downward, like a dense white cloud. In this act so much heat
becomes evolved as to make the phial feel sensibly warm to the hand.
When the crystallization is complete, the whole mass generally becomes
so solid, that, on inverting the bottle, not a drop of it will fall out.
If the crystallization should not immediately ensue on opening the
phial, this may instantly be effected by dropping into it a minute
crystal of the same salt. The experiment may be exhibited any number of
times afterwards, by merely placing the phial in boiling water, till the
salt it contains be again completely liquefied; and letting it stand, as
before, to cool.
204. _BORAX is a salt composed of boracic acid (28) and soda (200), and
is imported chiefly from the East Indies, in the form of a brownish
grey, impure, shapeless salt, of sweetish taste; or in detached
prismatic crystals, each about an inch in length._
Although borax has long been known as an article of traffic, there is
scarcely any production with the origin of which we have been, till
lately, less acquainted. It is found in a native, though impure state,
in a mountain lake, situated about fifteen days’ journey from the
capital of Thibet in the East Indies. This lake is so encompassed with
hills as to have no stream either falling into it or flowing from it.
The water is salt to the taste, and contains both borax and common salt;
and the edges and shallow parts are covered with a stratum of this
substance, which is dug up in considerable masses for exportation. It
has here the name of _tinkal_, and is usually brought into Europe
enveloped in a kind of fatty substance. The mode of refining it was for
a long time kept, by the Dutch and Venetians, amongst those secrets
which a want of sufficient research alone prevented from being generally
known. When refined, it is called _borax_.
The uses of borax are numerous. It is employed as a flux for metals,
being found to produce a more perfectly limpid fusion than any other
substance. For the same reason it is made an ingredient in the finest
kinds of glass, and particularly in some of the coloured glass pastes
which are manufactured in imitation of gems. But its chief use is to
jewellers and goldsmiths, to facilitate the soldering of gold and
silver. Borax is also used in medicine.
205. POTASH FAMILY.
Potash is an alkaline substance (42), of white colour, and of smell
somewhat resembling that which is perceived during the slaking of
quick─lime (137). It is extremely corrosive, and remarkably acrid to the
taste.
In a mineral state it is found only in combination with nitric acid
(30).
Potash principally exists under the form of a salt, in vegetable
substances; and is obtained by burning them, afterwards repeatedly
washing the ashes with water, and then filtering and evaporating these
to dryness. The appellation of potash was given to this salt from its
having formerly been prepared in large iron pots.
The uses to which it is applied are numerous. In chemistry it is
employed for a variety of purposes; and also in many arts and
manufactures, in scouring, washing, bleaching, dyeing, glass─making, and
several others. Its corrosive property is such that it is often used by
surgeons under the name of _potential cautery_, to open abscesses, and
to destroy useless or hurtful excrescences.
=Potash=, after it has been made red hot, is rendered whiter and more
pure. In this state it has the name of pearl ash.
206. _NITRE, or SALTPETRE, is a salt which consists of potash in
combination with nitric acid (30)._
_Its colour is whitish or limpid; and it does not liquefy by the action
of the air. It is usually observed in the form of fine capillary
crystals, though it is sometimes found in a massive state. When pure, it
crystallizes into six─sided prisms (Pl. II, Fig. 15) which have a
rectangular base. It is denominated by chemists_ nitrat of potash.
Nitre is found incrusted on the surface of the earth, in some parts of
India, Africa, and Spain, and, in such abundance, as to admit of being
swept off at certain seasons of the year, twice or three times a week.
In our own country it not unfrequently occurs in a state of white
efflorescence, on old plaster walls that are sheltered from rain. Nitre
is also produced in stables and cart─houses, from the mixture of animal
and vegetable substances in a state of putrescence.
Many kinds of plants, which grow in soils favourable to the production
of it, contain nitre: this is particularly the case with pellitory,
borage, and the large sunflower.
Immense quantities of nitre are annually required for the purposes of
war. From its constituting one of the most important substances in the
composition of gunpowder, it has been found necessary to adopt
artificial modes of procuring it. In several districts of the East
Indies there are places called saltpetre grounds. From these large
quantities of the earth are dug, and put into cavities through which
water is passed. This brings away with it the salt which the earth
contains, and which is afterwards separated from the water by boiling.
The East India Company, for more than a century past, has been under
engagements to import into this country, and supply the board of
ordnance, for his Majesty’s service, with 500 tons of nitre annually, at
given rates and prices in times of peace and war.
In France this article is obtained in what are called _nitrières_, or
nitre beds. These consist of the refuse of animal and vegetable
substances, which undergo putrefaction, mixed with calcareous and other
earths; and the nitre is obtained from them by water, as
above─mentioned.—The principal requisites for the formation of nitre are
said to be lime, animal and vegetable matters, heat, and an open, but
not too free communication with dry atmospheric air.
The discovery of _gunpowder_ has completely changed the modern art of
war. The earliest notice that has occurred respecting the use of this
article in Europe is, that it was employed in the wars of Germany,
somewhat before the year 1373. It is said, however, to have been known
in China long anterior to that period. Its component parts are nitre,
charcoal, and sulphur, in the proportion of seventy─six, fifteen, and
nine parts, in every hundred. These ingredients are first reduced to a
fine powder separately, and then mixed with water, so as to form a thick
paste. After this has dried a little, it is placed upon a kind of sieve
full of small holes, through which it is forced. By this process it is
divided into grains, the size of which depend of course upon the size of
the holes through which it has been squeezed. It afterwards undergoes
some other operations before it is ready for use.
Nitre is frequently administered in medicine; and it is used very
extensively in different arts. A mixture of equal parts of nitre and
tartar, burned together in a crucible, forms what is called _white
flux_, which is used for melting and reducing different kinds of
metallic substances. And a mixture of one part of nitre and two parts of
tartar burned in the same manner forms what is called _black flux_.
Nitre possesses antiseptic qualities in a considerable degree, whence it
is much used, in conjunction with common salt and bay salt, for the
preserving of animal food from putrefaction.
_Aqua─fortis_, or _nitric acid_ (30) as it is denominated by chemists,
is prepared from this mineral. The mode of obtaining it in large
manufactories is by distilling a mixture of nitre and clay in glass or
stone retorts, each capable of containing seventy or eighty pounds’
weight of this mixture. But the acid thus procured being weak and
impure, chemists, for nicer purposes, generally prepare it by
distilling, in a glass apparatus, a proportion of three parts of nitre
and one of sulphuric acid (24). The uses of aqua─fortis are various and
important. All kinds of metals, except gold and platina, are capable of
being dissolved in it. Hence, among other uses, it is employed by dyers,
for dissolving tin, and forming with madder a scarlet colour; and, by
hatters, for dissolving mercury (228) for some processes in the
preparation of hats. Jewellers use it for several purposes.
AMMONIA FAMILY.
207. _SAL─AMMONIAC, or MURIAT OF AMMONIA, is a salt compounded of
ammonia and muriatic acid (22). It is occasionally found in a state of
powder, sometimes in a massive form, and sometimes in very irregularly
shaped crystals, the primitive form of which is an octohedron (Pl II,
Fig. 5). It is, however, more frequently an artificial production from
the soot of burned animal matter._
The name of sal─ammoniac was acquired by this substance from its having
been found by the ancients in great abundance amongst sand near the
temple of Jupiter Ammon, in Africa. It is at present found in Persia;
and, accompanying sulphur, amongst volcanic matter near Mount Vesuvius.
This salt was formerly imported from Egypt in the form of conical
loaves, or of round cakes, which were convex on one side and concave on
the other; but it is now made in Europe, by burning at the same time
soot, bones, oil, and salt. The deposit formed by the vapour consists of
sal─ammoniac, in conjunction with other substances, which are separated
from it by a subsequent process. When good, it is white, transparent,
and dry within; and externally of yellowish grey, or blackish colour.