CLASS II.—SALTS.
ORDER I.—EARTHY SALTS.
ALUMINE FAMILY.
197. ALUM is a substance of yellowish or greyish white colour, usually opaque, but sometimes transparent. When purified, it consists of slender, irregular, hair-shaped fibres, and has a sweetish, astringent taste.
The alum of commerce is an artificial production from the different kinds of stones which contain it. That called Roman alum, from its being procured from the neighbourhood of Rome, is usually considered preferable to the other sorts; but good alum of our own manufacture is equal to it in quality. The Levant, or Roche alum, is said to have had its name from the village of Rocca, the present Edessa, in Syria.
There is a famous alum mine at Tolfa, near Civita Vecchia, in Italy. The alum is obtained from this mine nearly in a pure state; and it is so extremely hard, that it can only be wrought by means of pickaxes, and gunpowder. At Solfatara, near Naples, and in other volcanic countries, an abundance of alum is found, in a state of efflorescence, from the lava.
The alum of our own country is manufactured from a kind of slaty stone which is found near Whitby, in Yorkshire. This manufactory was first established about the conclusion of the sixteenth century, by Sir Thomas Chaloner, who is supposed to have obtained his knowledge of the process, from the alum works which had then lately been introduced into Germany and Spain. The rock of alum slate, near Whitby, is supposed to be nearly twelve miles in extent: and affords an abundant supply of alum. The workmen tear open the rock; after which the different fragments are loosened, in the form of slaty leaves or plates, that are of a dark grey colour. To obtain the alum, a bed of fagots is formed from ten to twelve feet in depth. By the side of this a scaffold is erected, which enables the workmen to form a pile of mineral about fifty feet long, and forty feet high. While this pile is forming, the fagots are lighted. By the gradual operation of the heat, a calcination takes place, in consequence of which the alum is afterwards rendered capable of being more easily separated than it otherwise would be from the stone in which it was contained, and from other extraneous matters that are combined with it. After this, the mineral is washed in shallow vessels, so arranged that the water may be poured from one into the other. By this process the alum becomes suspended in the water, while all the earthy particles subside to the bottom. The next operation is to evaporate the water saturated with alum. This is done by boiling it in large leaden caldrons, fixed, on cast iron bars, over a furnace. As soon as the contents of the caldrons are brought to a proper state, they are drawn off into casks, where the alum concretes into a mass. The hoops are then taken off, and the alum is broken and left to dry; after which it is packed in casks for sale.
Alum is an article of indispensable importance to dyers, not only on account of its cleansing and opening the pores of the substances to be dyed, and thus rendering them fit to receive the colouring particles, but also from its more essential property of fixing the colours in such manner that they cannot afterwards be washed out. By tanners it is in great request for giving firmness to the skins after they have been rendered flaccid in the lime-pits. It is employed in the manufacture of paper, and by engravers, and other artists. In the making of candles, alum is added to the tallow, to render it glossy, and to give it greater firmness and consistence; and, mixed with cream, it aids the separation of butter. It has a tendency to retard ignition. Paper soaked in alum water does not easily take fire, and is thereby better fitted for the preservation of gunpowder. Such paper is likewise used in the whitening of silver, and the silvering of brass. It has been recommended that ladies’ muslin dresses should be dipped in a solution of this substance, for the purpose of rendering them less liable to catch fire. A solution of alum also retards the putrefaction of animal substances, and affords useful, as well as economical, means of preserving natural productions that are imported from foreign countries. Alum is frequently mixed with paste, to prevent its losing its tenacity by the absorption of moisture. It is asserted that bakers occasionally use it as an ingredient in bread, and that its presence may be discovered by thrusting a heated knife into a loaf before it is cold: if free from alum, scarcely any alteration will be visible on the blade, but if the contrary, the surface, when cool, will appear slightly covered with an incrustation of alum. A very important purpose to which alum may be applied is in the purifying and sweetening of water that has become fetid and unfit for use; from five to ten grains of burned alum, and double or treble that quantity of pounded charcoal, will correct the fetor of a gallon of water. Printers’ cushions, and the blocks used for the printing of calicos, are rubbed with burned alum to remove any greasiness, which otherwise would prevent the ink or colour from sticking. This substance is also occasionally employed by surgeons to stop the bleeding of small vessels, to corrode fungous or proud flesh, and for other purposes in medicine.
198. MAGNESIA FAMILY.
This is a family of minerals which comprehends all the combinations of magnesia with acids.
When freed from extraneous matters, magnesia is a powdery substance of limpid white colour.
199. EPSOM SALTS, or SULPHAT OF MAGNESIA, consist of magnesia in conjunction with sulphuric acid ([24]).
It is said that Epsom salts have been found in the Alps, and in Switzerland, under a powdery form, and sometimes even in masses, or a state of incrustation on stones and rocks. They are, however, chiefly found dissolved in mineral waters, and particularly in those at Epsom in Surrey, and Sedlitz in Bohemia. Their taste is bitter and unpleasant. So little are they affected by exposure to the air, that the Abbé Haüy kept some by him for more than twelve years without any sensible alteration.
These salts are much used in medicine, and are sometimes manufactured from the waters of Epsom ([290]) and Sedlitz ([289]), but more frequently, and in much greater abundance, from sea-water.
The magnesia of the shops is prepared by dissolving Epsom salts in water, and adding to the solution half their weight of potash ([205]). The substance that sinks to the bottom is magnesia; and this, washed with a sufficient quantity of water and dried, has the appearance of a light, soft, and white powder, of insipid taste.
Magnesia is used in medicine, both in a simple state and when calcined or burned. It is also employed in some chemical processes; and is in considerable request in the manufacture of enamel and porcelain. If putrid water be agitated with a small quantity of magnesia, it will lose a considerable portion of its bad taste and smell.
200. SODA FAMILY.
Soda, like potash ([205]), is an extremely caustic alkali ([42]). It has a greyish white colour, and agrees exactly with potash ([205]) in taste, smell, and corrosive quality, but it is not so heavy.
In a mineral state soda has hitherto been found only in combination with some acid.
Common salt ([202]) is a compound of soda with muriatic acid ([29]).
The soda of commerce is obtained from sea-water; and from the ashes of different kinds of plants that grow on the sea-shores, but particularly from that called salsola soda, which is found in great abundance on the coasts of the southern parts of Europe; and from which it has its name. It is sometimes called barilla, from the salsola soda being so denominated in Spain.
This alkali is of essential use in the arts. When melted with flint or 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.
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.
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.