Part 12

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.

Sal─ammoniac is applied to many useful purposes. Occasionally it is used 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.