Chapter II: Part 2

Alkaline air is produced by means of heat from caustic volatile alkali, and also from a mixture of sal-ammoniac and slaked lime, in the proportion of about one-fourth of the former to three-fourths of the latter. In this case the marine acid in the sal-ammoniac unites with the calcareous earth, and the volatile alkali (probably with the assistance of the water) takes the form of air.

This species of air is heavier than inflammable air, but lighter than any of the acid airs. Like them, however, it dissolves ice, and deprives alum, and some other saline substances, of the water which they contain. United with fixed air, it makes the concrete volatile alkali; with marine acid air, the common sal-ammoniac; and with water, the caustic volatile alkali.

The electric spark, or a red heat, converts alkaline air into three times its bulk of inflammable air; and the calces of metals are revived in alkaline, as well as in inflammable air; but there remains about one-fourth of its bulk of phlogisticated air. These facts shew that alkaline air consists chiefly of phlogiston.

_Miscellaneous Observations relating to Air._

The _nitrous_ acid may be exhibited in the form of air, as well as the vitriolic, the marine, and the fluor acids. But it cannot be confined even by mercury, which it instantly dissolves. It may, however, in some measure, be confined in a dry glass vessel, from which it will in a great measure expel the common air. This nitrous acid air is that red vapour, which is produced by the rapid solution of bismuth, and some other metals in the nitrous acid. But the vegetable acid cannot be exhibited in the form of air. It is only capable of being converted into vapour, like water: and in the common temperature of our atmosphere, returns to a state of fluidity.

Different kinds of air which have no affinity to each other, when once mixed together will not separate, notwithstanding any difference of specific gravity. Such is the case of a mixture of inflammable and dephlogisticated air, and even of inflammable and fixed air. Without this property also, the phlogisticated air, which constitutes the greatest part of our atmosphere, being specifically lighter than dephlogisticated air, of which the other part of it consists, would separate from it, and ascend into the higher regions of the atmosphere. Inflammable air, however, will not mix with acid or alkaline air.

Different kinds of air are expanded differently by the same degrees of heat; dephlogisticated air the least, and alkaline air the most.

If any fluid, as water, spirit of wine, or even mercury, be heated in a porous earthen vessel, surrounded by any kind of air, the vapour of the fluid will pass through the vessel _one_ way, while the air passes the _other_; and when the operation ceases, with respect to the _one_, it likewise ceases with respect to the _other_.

LECTURE XI.

_Of Liquid Substances_;

AND FIRST OF

_WATER_.

Having considered all the substances that are usually found in the form of _air_, I come to those that are generally in a _fluid_ form, beginning with _water_, which is the principal, if not the only cause of fluidity to all the other substances that I shall place in this class.

Pure water is a liquid substance, transparent, without colour, taste, or smell; and with different degrees of heat and cold may be made to assume the three forms of a solid, of a fluid, and of air. Below 32 deg. of Fahrenheit it is ice, and above 212 deg. it is vapour; so that in an atmosphere below 32 deg. it never could have been known to be any thing else than a peculiar kind of stone, and above 212 deg. a peculiar species of air.

In passing from the state of a solid to that of a liquid, water absorbs a great quantity of the principle, or matter, of _heat_, which remains in it in a _latent_ state; and in passing from a state of fluid to that of vapour, it absorbs much more; and this heat is found when the processes are reversed. It has been observed, that when water becomes vapour, it takes the form of small globules, hollow within, so as to be specifically lighter than air.

The degree of heat at which water is converted into vapour depends upon the pressure of the atmosphere; so that in vacuo, or on the top of a high mountain, it boils with little heat; and when compressed, as in Papin's digester, or in the bottom of a deep pit, it requires much heat. In the former case the restoring of the pressure will instantly put a stop to the boiling, and in the latter case the removing of the pressure will instantly convert the heated water into vapour.

The ease with which water is converted into vapour by heat, has given a great power to mechanicians, either by employing the natural pressure of the atmosphere, when steam is condensed under a moveable pistern, in an iron cylinder, which was the principle of the old fire-engine, or by employing the elastic power of steam to produce the same effect, which is the principle of Mr. Watt's steam engine.

Water was long thought to be incompressible by any external force, but Mr. Canton has shewn that even the pressure of the atmosphere will condense it very sensibly.

We do not know any external force equal to that by which water is expanded when it is converted into ice, or into vapour. For though the particles of water approach nearer by cold, yet when it crystallizes, the particles arrange themselves in a particular manner, with interstices between them; so that, on the whole, it takes up more room than before.

Water has an affinity to, and combines with, almost all natural substances, aerial, fluid, or solid; but most intimately with acids, alkalies, calcareous earth, and that calx of iron which is called _finery cinder_, from which the strongest heat will not expel it.

It has been supposed by some, that by frequent distillation, and also by agitation, water may be converted into a kind of earth; but this does not appear to be the case. It has also of late been thought, that water is resolvable into dephlogisticated and inflammable air; but the experiments which have been alleged to prove this do not satisfy me; so that, for any thing that appeared till very lately, water might be considered as a simple element. By means of heat, however, it seems to be resolvable into such air as that of which the atmosphere consists, viz. dephlogisticated and phlogisticated, only with a greater proportion of the former.

Water, with respect to specific gravity and temperature, has generally been made the standard to all other substances; its freezing and boiling points being the limits by means of which thermometers are graduated. Other substances have also been compared with water, as a standard, with respect to the capacity of receiving heat, and retaining it in a latent state, as will be shewn when we consider the subject of heat.

LECTURE XII.

_Of the Nitrous Acid._

Under the head of _liquids_ I shall consider _acids_ and _alkalis_, though some of them may be exhibited in the form of air, and others in a solid form. These two chemical principles are formed to unite with one another, and then they constitute what is called a _neutral salt_.

Both acids and alkalis are distinguishable by their taste. Another test, and more accurate, is, that acids change the blue juices of vegetables red, and alkalis turn the syrup of violets green.

Acids are generally distinguished according to the three kingdoms to which they belong, viz. _mineral_, _vegetable_, and _animal_. The mineral acids are three, the _nitrous_, the _vitriolic_, and the _marine_.

The nitrous acid is formed by the union of the purest inflammable air, or the purest nitrous air, with dephlogisticated air. But it is usually procured from nitre by means of the vitriolic acid, which, seizing its base, expels the nitrous acid in a liquid form. On this account this acid is said to be weaker than the vitriolic.

If the nitrous acid be made to pass through a red-hot earthen tube, it will be decomposed, and the greatest part of it be converted into dephlogisticated air.

Like all other acids, the nitrous acid has a strong affinity to water; but it is not capable of so much concentration as the vitriolic. It is generally of an orange or yellow colour; but heat will expel this colour in the form of a red vapour, which is the same acid in the form of air, and loaded with phlogiston; and therefore when it is colourless it is said to be dephlogisticated. But the colourless vapour exposed to heat, or to light, will become coloured again; and the liquid acid imbibing this coloured vapour, becomes coloured as before. This acid tinges the skin of a yellow colour, which does not disappear till the epidermis be changed.

The nitrous acid unites with phlogiston, alkalis, metallic substances, and calcareous earth.

By means of its affinity with phlogiston it occasions that rapid accension called _detonation_, when any salt containing this acid, especially nitre, is applied to hot charcoal, or when charcoal is put to hot nitre. In fact, the charcoal burns so rapidly by means of the dephlogisticated air supplied by the nitre.

A mixture of sulphur assists the accension of these substances, and makes gunpowder, in the explosion of which much nitrous or phlogisticated air is suddenly produced, and expanded by the heat. The application of this force, both to useful and destructive purposes, is well known. If, instead of nitre, a salt made with dephlogisticated marine acid be made use of, the explosion is more easily produced, and is much more violent. Friction will do this as well as heat.

Nitre also enters into the composition of _pulvis fulminans_, viz. three parts nitre, two of dry alkali, and one of sulphur. This composition melts, and yields a blue flame, before it explodes.

By means of the affinity of the nitrous acid to _oil_, another substance containing phlogiston, it is capable of producing not only a great heat, but even a sudden flame, especially when mixed with a little vitriolic acid.

Nitrous acid dissolves all metallic substances except gold and platina, and in the solution nitrous air is produced.

The particular kinds of saline substances formed by the union of the nitrous acid with the several metals and earths may be seen in tables constructed for the purpose. They are all deliquescent.

LECTURE XIII.

_Of the Vitriolic Acid._

The vitriolic acid, so called because it was originally procured from _vitriol_, is now generally procured from sulphur; the dephlogisticated part of the air uniting with it in the act of burning.

That dephlogisticated air is essential to this acid is evident from the decomposition of it; for if the vapour of it be made to pass through a red-hot earthen tube, a great quantity of dephlogisticated air is procured.

This acid has a strong affinity to water, with which it unites with much heat; and it is capable of greater concentration, or of being made specifically heavier, than any other acid. When pure, it is entirely free from colour and smell, owing, probably, to its being free from phlogiston, which is inseparable from the nitrous or marine acids.

The vitriolic acid will dislodge the nitrous, or marine, or any other acid, from their earthy or metallic bases; from which property it is called the strongest of all the acids.

By means of the superior affinity of the vitriolic acid to earths, and especially to _terra ponderosa_, the smallest quantity of it in water may be discovered by a solution of this earth in the marine acid. In this acid the terra ponderosa is held in perfect solution; but with the vitriolic acid it forms a substance that is insoluble in water, and therefore it instantly appears in the form of a white cloud.

Perhaps chiefly from the strong affinity which this acid has with water, _pyrophorus_, consisting of a mixture of alum and several substances containing phlogiston, takes fire spontaneously on exposure to the air. It is commonly made of three parts of alum and one of brown sugar, or of two parts alum, one of salt of tartar, and one of charcoal. They must be heated till they have for some time emitted a vapour that burns with a blue flame.

The saline substances produced by the union of this acid with the several earths and metals, are best exhibited in tables constructed for the purpose. When united to three of the metals, viz. iron, copper, and zinc, they are called _vitriols_, green, blue, and white. And all the substances which this acid unites with crystallize, and do not deliquesce.

This acid unites with oil, and the mixture is always black.

When any substance containing phlogiston is heated in the vitriolic acid, another species of the acid, called _sulphureous_, is formed, of a pungent smell. In reality, it is water impregnated with vitriolic acid air. It makes, however, a distinct species of acid, and is dislodged from its base by most of the others.

_Of the Marine Acid._

The marine acid is procured from common salt by the vitriolic acid, which unites with its base, the fossil alkali.

This acid is generally of a straw-colour; but this is owing to an impregnation with some earthy matter, most of which it readily dissolves, especially the metallic ones. It is less capable of concentration than the vitriolic or nitrous acids, perhaps from a more intimate union of phlogiston with it. No heat can extract from it any dephlogisticated air.

Though this is denominated a weaker acid than the nitrous, yet it will take silver, lead, or mercury, from their union with the nitrous acid. Upon this principle, a solution of these metals in the nitrous acid will readily discover whether any water contains the marine acid, the latter uniting with the metal dissolved in the former, and forming with it, if it be silver, a _luna cornea_; which being a substance insoluble in water, discovers itself by a cloudy appearance.

The union of the marine acid with earths forms salts that easily deliquesce, but with the metals such as are capable of crystallization; and so also is that formed by the union of this acid to terra ponderosa.

Neither this acid nor the nitrous will dissolve gold or platina; but a mixture of them, called _aqua regia_, will do it.

The marine acid has a strong affinity to dephlogisticated air, and will take it from manganese and other substances; and with this union it becomes a different acid, called _dephlogisticated marine acid_, being water impregnated with dephlogisticated marine acid air, described above.

LECTURE XIV.

_Of the Vegetable Acids, and others of a less perfect nature._

The principal of the vegetable acids are the _acetous_ and the _tartareous_. The acetous acid is the produce of a peculiar fermentation of vegetable substances, succeeding the _vinous_, in which ardent spirit it is procured, and succeeded by the _putrefactive_, in which volatile alkali is generated.

Thus wine is converted into vinegar. Crude vinegar, however, contains some ingredient from the vegetable substances from which it was procured: but distillation separates them, and makes the vinegar colourless; though some of the acid is lost in the process.

The acetous acid is concentrated by frost, which does not affect the proper acid, but only the water with which it is united. It may likewise be concentrated by being first combined with alkalies, earths, or metals, and then dislodged by a stronger acid, or by mere heat. Thus the acetous acid, combined with vegetable alkali, forms a substance that is called the _foliated earth of tartar_; and it may be expelled from it by the vitriolic acid. When combined with copper it makes _verdigris_; and from this union heat alone will expel it in a concentrated state. The acetous acid thus concentrated is called _radical vinegar_. Still, however, it is weaker than any of the preceding mineral acids.

Several vegetables, as lemons, sorrel, and unripe fruit, contain acids, ready formed by nature, mixed with some of the essential oil of the plants, which gives them their peculiar flavours. All these acids have peculiar properties; but it is not necessary to note them in this very general view of the subject. Like vinegar, these acids may be concentrated by frost, and also by a combination with other substances, and then expelled by a stronger acid.

The _acid of tartar_ is very similar to that of vinegar. Tartar, from which it is procured, is a substance deposited on the inside of wine-casks, though it is also found ready formed in several vegetables. It consists of the vegetable alkali and this peculiar acid. When refined from its impurities, it is called _crystals_, or _cream of tartar_. The acid is procured by mixing the tartar with chalk, or lime, which imbibes the superfluous acid, and this is expelled by the acid of vitriol. Or it may be procured by boiling the tartar with five or six times its weight of water, and then putting the acid of vitriol to it. This unites with the vegetable alkali, and forms vitriolated tartar; and the pure acid of tartar may be procured in crystals, by evaporation and filtration, equal in weight to half the cream of tartar. This acid of tartar is more soluble in water than the cream of tartar.

This acid, united to the mineral alkali, makes _Rochelle salt_.

Every kind of wood, when distilled, or burned, yields a peculiar acid; and it is the vapour of this acid that is so offensive to the eyes in the smoke of wood.

A peculiar acid is obtained from most vegetable substances, especially the farinaceous ones, and from sugar, by distillation with the nitrous acid. This seizes upon the substance with which the acid was united, and especially the phlogiston adhering to it, and then the peculiar _acid of sugar_ crystallizes. Thus with three parts of sugar, and thirty of nitrous acid, one part of the proper acid of sugar may be obtained. By the same process an acid may be procured from camphor.

The _bark of oak_, and some other vegetable substances, especially nut-galls, contain a substance which has obtained the name of _the astringent principle_; the peculiar property of which is, that it precipitates solutions of iron in the form of a black powder, and in this manner _ink_ is made. But by solution in water and evaporation, crystals, which are a proper _acid of galls_, may be obtained.

_Amber_ is a hard semitransparent substance, chiefly found in Prussia, either dug out of the earth, or thrown up by the sea. It is chiefly remarkable for its electrical property; but by distillation in close vessels there sublimes from it a concreted acid, soluble in 24 times its weight of cold water. Amber seems to be of vegetable origin, and to consist of an oil united to this peculiar acid.

The acids I shall mention next are of a mineral origin; but being of a less perfect nature as acids, I shall only just note them here.

_Borax_ is a substance chiefly found in a crystallized state in some lakes in the East Indies. It consists of the mineral alkali and a peculiar acid, which may be separated, and exhibited in white flakes, by putting acid of vitriol to a solution of it in water. This acid has been called _sedative salt_, from its supposed uses in medicine. It is an acid that requires fifty times its weight of water to dissolve it.

Several other mineral substances, as _arsenic_, _molybdena_, _tungsten_, and _wolfram_, in consequence of being treated as the preceding vegetables ones, have been lately found to yield peculiar acids. They are also produced in a concrete state, and require a considerable proportion of water to make them liquid; but as the water in which they are dissolved turns the juice of litmus red, and as they also unite with alkalis, they have all the necessary characteristics of acids.

LECTURE XV.

_Of the Phosphoric Acid._

The most important acid of _animal_ origin, though it has lately been found in some mineral substances, is the _phosphoric_.

Phosphorus itself is a remarkable substance, much resembling sulphur, but much more inflammable. It has been procured chiefly, till of late, from urine, but now more generally from _bones_, by means of the vitriolic acid, which unites with the calcareous earth of which bones consist, and sets at liberty the phosphoric acid, or the base of that acid, with which it was naturally combined. The acid thus procured, mixed with charcoal, and exposed to a strong heat, makes phosphorus.

This substance burns with a lambent flame in the common temperature of our atmosphere, but with a strong and vivid flame if it be exposed to the open air when moderately warm. In burning it unites with the dephlogisticated air of the atmosphere, and in this manner the purest phosphoric acid is produced.

This acid is also procured in great purity by means of the nitrous or vitriolic acids, especially the former, which readily combines with the phlogiston of the phosphorus, and thus leaves the acid pure. In this process phlogisticated air is produced.

This acid is perfectly colourless, and when exposed to heat loses all its water, and becomes a glassy substance, not liable to be dissipated by fire, and readily uniting with earths.

United to the mineral alkali, it forms a neutral salt, lately introduced into medicine. United to the mineral and vegetable alkalis naturally contained in urine, it has obtained the name of _microcosmic salt_, frequently used as a flux for mineral substances with a blow-pipe.

Besides the phosphoric, there are other acids of an animal origin; as that of _milk_, that of _sugar of milk_, that of the _animal calculus_, and that of _fat_.

The acid of milk is the sour whey contained in butter-milk, which, by a tedious chemical process, may be obtained pure from any foreign substance.

The sugar of milk is procured by evaporating the whey to dryness, then dissolving it in water, clarifying it with whites of eggs, and evaporating it to the consistence of honey. In this state white crystals of the acid of sugar of milk will be obtained.

By distilling these crystals with nitrous acid, other crystals of the proper _acid of sugar of milk_ will be obtained, similar to those of the acid of sugar.

If the human calculus be distilled, it yields a volatile alkali, and something sublimes from it which has a sourish taste, and therefore called the _acid of the calculus_. It is probably some modification of the phosphoric acid.

Animal fat yields an acid by distillation, or by first combining it with quick-lime, and then separating it by the vitriolic acid. Siliceous earth is corroded by this acid.

LECTURE XVI.

_Of Alkalis._

The class of substances that seems particularly formed by nature to unite with acids, and thereby form _neutral salts_, are the _alkalis_. They have all a peculiar acrid taste, not easily defined. They change the blue juices of vegetables green, or purple, and in common with acids have an affinity with water, so as to be capable of being exhibited in a liquid form; though when this water is expelled by heat, some of them will assume a solid form.

Alkalis are of two kinds; the _fixed_, which have no smell, and the _volatile_ which have a pungent one.

The fixed alkalis are of _vegetable_ or _mineral_ origin. When in a solid form, they both melt with a moderate heat, and uniting with earthy substances, make _glass_. With an intense heat they are volatilized.

Vegetable alkali is procured by burning plants, and lixiviating the ashes; a purer kind by the burning of tartar, hence called _salt of tartar_; but the purest of all is got by the deflagration of nitre; the charcoal uniting with the acid as it assumes the form of dephlogisticated air, and the alkali being left behind.

Mineral alkali is found in ashes of sea-weed. It is likewise the basis of sea-salt; from which it is separated by several processes, but especially by the calx of lead, which has a stronger affinity with the marine acid with which it is found combined.

Alkalis united with fixed air are said to be _mild_, and when deprived of it _caustic_, from their readiness to unite with, and thereby _corrode_, vegetable and animal substances. To render them caustic, they are deprived of their fixed air by quick-lime; and in this state they unite with oils, and make _soap_.

Alkalis have a stronger affinity with acids than metals have with them; so that they will precipitate them from their solutions in acid menstruums.

The vegetable fixed alkali has a strong attraction to water, with which it will become saturated in the common state of our atmosphere, when it is said to _deliquesce_; and having the appearance of _oil_, the salt of tartar is thus said to become _oil of tartar per deliquium_. On the other hand, the mineral, or fossil alkali, is apt to lose its water in a dry atmosphere, and then it is said to _effloresce_. In this state it is often found on old walls.

Volatile alkali is procured by burning animal substances; in Egypt (from whence, as contained in _sal ammoniac_, we till of late imported it) from camel's dung; but now from bones, by distillation. To the liquor thus procured they add vitriolic acid, or substances which contain it. This acid unites with the alkali, and common salt being put to it, a double affinity takes place. The vitriolic acid uniting with the mineral alkali of the salt, makes _Glauber salt_, and the marine acid uniting with the volatile alkali, makes _sal ammoniac_. Slaked lime added to this, unites with the marine acid of the ammoniac, and sets loose the volatile alkali in the form of _alkaline air_, which combining with water, makes the liquid caustic volatile alkali. If chalk (containing calcareous earth united with fixed air) be mixed with the sal ammoniac, heat will make the calcareous earth unite with the marine acid, while the fixed air of the chalk will unite with the volatile alkali, and assume a solid form, being the _sal volatile_ of the apothecaries.

LECTURE XVII.

_Of Liquid Inflammable Substances._

Of liquid inflammable substances the principal is _spirit of wine_, sometimes called _ardent spirit_, and, when highly rectified, _alcohol_. It is obtained from vegetable substances by their going through the vinous fermentation. It is considerably lighter than water, colourless, and transparent, has a peculiar smell and taste, and the property of inebriating.

Ardent spirit seems to consist of a peculiar combination of phlogiston and water; for when the vapour of it is made to pass through a red-hot earthen tube, it is resolved into water and inflammable air. It is highly inflammable, and burns without smoke, or leaving any residuum; and in the act of burning its phlogiston so unites with dephlogisticated air as to make fixed air.

Ardent spirit mixes readily with water in all proportions, and also with essential oils, and balsams or resins, which are the same thing inspissated.

By its affinity with essential oils, ardent spirit extracts them froth aromatic plants; and these liquors have obtained the name of _tinctures_.

When the tinctures are distilled, the more volatile parts of the essential oils, which come over in distillation, have acquired the name of _waters_; as _Lavender water_, _Rosemary water_, &c. and what remains in the still is called the _extract_ of the plant. If the tinctures be diluted with much water, the resinous part of the plant will be obtained pure, and separated from the extractive part, which will remain dissolved in the water, while the resin separates from it.

Spirit of wine will not dissolve the gummy parts of vegetables; and by this means the gummy substances may be separated from their solutions in water, the spirit uniting with the water only. On the other hand, if resins be dissolved in spirit of wine, the affusion of water will separate them. By means of the affinity of spirit of wine with water, it will seize upon the water in which several salts are dissolved, and thus produce an instant crystallization of them.

Salt of tartar has a greater affinity to water than spirit of wine, and by extracting water from it, will assist in concentrating it; but the best method of rendering spirit wine free from water is distillation, the ardent spirit rising before the water.

Spirit of wine mixed with the vitriolic and other mineral acids, renders them milder, and thereby more proper for certain medicinal uses. This is called _dulcifying_ them.

Spirit of wine is a powerful antiseptic, and is therefore of use to preserve vegetable and animal substances from putrefaction.

_Of AEther._

If spirit of wine be distilled with almost any of the acids, the produce is a liquor which has obtained the name of _AEther_, from its extreme lightness and volatility, being much lighter, and more volatile, than any other fluid that we are acquainted with. It is highly inflammable, but the burning of it is accompanied with smoke, and some soot; and on this account it is a medium between spirit of wine and oil, the acid having taken from the spirit of wine part of the water that was essential to it, at the same time that it communicated something of its acid peculiarly modified; since aethers have different properties according to the acids by which they are made; as the _vitriolic_, the _nitrous_, the _marine_, and the _acetous_. No aether, however, can be made from the marine acid till it has been in some measure dephlogisticated; from which it may be inferred, that dephlogisticated air is necessary to the composition of aether. Vitriolic aether is the most common, in consequence of the process by which it is made being the easiest.

AEther does not mix with water in all proportions, like spirit of wine, but ten parts of water will take up one of aether. It easily mixes with all oils.

It is something remarkable, that though aether will not dissolve gold, it will take from aqua regia the gold that has been previously dissolved in it.

By the quick evaporation of aether a considerable degree of cold may be procured; and on this principle it has sometimes been applied to relieve the head-ach and other pains.

LECTURE XVIII.

_Of Oil._

Oil is a liquid inflammable substance, of great tenacity, disposed to pour in a stream rather than in drops. It is little, if at all, soluble in water. It burns with smoke and soot, and leaves a residuum of a coaly substance. It consists of acid and water combined with phlogiston.

All oil is the produce of the vegetable or animal kingdom, no proper mineral substance containing any of it.

By distillation oil is in part decomposed, and by this means the thicker kinds of oil are rendered thinner and more volatile, the acid, to which their consistence is chiefly owing, being lost in the process. By repeated distillation it is supposed that all oils may be brought almost to the state of aether, and even of ardent spirit.

Acids act powerfully upon oils, but very differently, according to the nature of each. Alkalies also combine with oils, and the less thin and volatile they are, the more easily are they soluble in alkalies. The union of alkali and oil makes _soap_. All oil dissolves sulphur, and with it makes what is called a _balsam_. Oils also dissolve metallic substances, but most sensibly copper and lead. United with the calx of lead, it is used in painting.

Oil not readily mixing with water, it will diffuse itself over its surface, and, notwithstanding its tenacity, it will do this very rapidly, and to a great extent; and then it has the extraordinary effect of preventing the action of the wind upon the water, so as to prevent the forming of waves. If a quantity of oil and water be put into a glass vessel and swung, the surface of the water below the oil will be seen to change with respect to the vessel, but not that of the oil. If spirit of wine be put upon them, that will be at rest, and both the lower fluids in motion.

Vegetable oil is of two kinds, the _soft_, or _mild_, which has little or no taste or smell, and the _essential_ oil, which is thin, and retains the smell and taste of the plant from which it was extracted.

Mild or sweet oil is expressed from the grains or kernels of vegetables, and requires a considerable degree of heat to convert it into vapour, in which state alone it is capable of being inflamed.

_Essential oil_ is volatile in the heat of boiling water, and is generally obtained by means of distillation from the most odoriferous sorts of plants; but is sometimes found in their vesicles, as in the rind of an orange. The strong taste of this kind of oil arises from the disengaged acid which abounds in it; and by this means it is soluble in spirit of wine, which sweet oil is not; but it loses much of this property by repeated distillations. By long exposure to the air it loses its more volatile parts, and thereby approaches to the nature of a resin. This volatile odoriferous principle has been called the _spiritus rector_ of the plant.

The essential oils of different plants differ much in their specific gravity, and also in the manner by which they are affected by cold, some being heavier and others lighter than water, and some being more difficultly, and others more easily, congealed. Though the differences with respect to _weight_ and _consistency_ in these oils is probably owing to the state of the acid that is combined with them, these two properties are wholly independent of each other; some essential oils being very thin and yet heavy, and others thick and yet light. Essential oils are used in perfumes, and also in medicine, acting powerfully the nervous system.

Essential oils are very apt to be adulterated. If it be with sweet oil, it may be discovered by evaporation on white paper, or by a solution in spirit of wine, which will not act upon the sweet oil. If spirit of wine be mixed with it, it will be discovered by a milky appearance upon putting water to it, which uniting with the spirit, will leave the oil much divided. If oil of turpentine, which is the cheapest of essential oils, be mixed with any of the more valuable kinds, it will be discovered by evaporation; a strong smell of turpentine being left on the paper, or cloth, upon which the evaporation was made.

Animal oil, like the vegetable, is of two kinds; the first _butter_, or _fat_, which is easily congealed, owing to the quantity of acid that is intimately combined with it. It resembles the sweet oil of vegetables in having no smell or taste. The other kind of animal oil is extracted by distillation from the flesh, the tendons, the bones, and horns, &c. of animals. It differs essentially from the other kind of animal oil, by containing an alkali instead of an acid. By repeated distillation it becomes highly attenuated and volatile; and in this state it is called the _oil of Dippel_, the discoverer of it.

All oil exposed to much heat is in part decomposed, and acquires a disagreeable smell; and in this state it is said to be _empyreumatic_: but this property is lost by repeated distillations.

Besides the vegetable and animal oils above described, there is a fossil oil called _bitumen_, the several kinds of which differ much in colour and consistence; the most liquid is called _petroleum_, from being found in the cavities of rocks, and the more solid kinds are _amber_, _jet_, _asphaltum_, and _pit-coal_. When distilled, the principal component parts of all these substances are an oil and an acid. But all fossil oil is probably of vegetable or animal origin, from masses of vegetables or animals long buried in the earth. Their differences from resins and other oily matters are probably owing to _time_; the combinations of mineral acids and oils so nearly resembling bitumens, the principal difference being their insolubility in spirit of wine.

That the most solid of these, as amber, has been formerly in a liquid state, is evident, from insects and other substances being frequently found in them; and pit-coal has been often found with both the internal texture and external appearance of wood; so that strata of pit-coal have probably been beds of peat in some former state of the earth.

LECTURE XIX.

_Of Solid Substances._

All solid substances are capable of becoming fluid by heat, and most of them may thereby be reduced into a state of vapour, or air; and in passing from a fluid into a solid state their component parts assume a particular mode of arrangement, called _crystallization_, which differs according to the nature of the substance; so that all solids, especially if they be suffered to concrete slowly, may be called _crystals_.

Exclusive of _salts_, which have been considered already, as formed by the union of acids and alkalis, solids in general have obtained the names of _earths_, or _stones_, which differ only in their texture; and they are distinguished into those that are _metallizable_, or those that are not; the former being called _ores_, and the latter simply _earths_; the principal of which are the _calcareous_, _siliceous_, _argillaceous_, _magnesia_, _terra ponderosa_, and a few others which have been discovered lately, but have not been much examined.

_Of Calcareous Earth._

Calcareous earth is found in the shells of fishes, the bones of animals, chalk, lime-stone, marble, and gypsum: but all calcareous earth is supposed to be of animal origin; and beds of chalk, lime-stone, or marble, are thought to have been beds of shells formed in the sea, in some pristine state of the earth.

The calcareous earth which is found in shells, lime-stone, and marble, is combined with fixed air, discovered by effervescing with acids. To obtain it perfectly pure, the earth must be pounded and washed with water, in order to free it from any saline substance which may be contained in it, then dissolved in distilled vinegar, and precipitated by mild alkalies. Lime-stone exposed to heat loses about half its weight, in fixed air and water, and the remainder, called _quick-lime_, attracts water very powerfully, and their union is attended with much heat, after which it dissolves into a fine powder called _slaked lime_. If it be left exposed to the atmosphere, it will of itself, by gradually imbibing moisture, fall into the state of powder.

Water dissolves about one seven hundredth part of its weight of quick-lime, and is then called _lime-water_. Exposed to the air, a crust will be formed on its surface, which is found to consist of calcareous earth and fixed air.

Lime and water mixed with sand make _mortar_, by which means different stones may be made to cohere as one mass, which is the most valuable use of this kind of earth.

Calcareous earth, united with vitriolic acid, makes _gypsum_; and this substance pounded and exposed to heat, parts with its water, and is then called _plaister of Paris_. In this state, by imbibing water again, it becomes a firm substance, and thus is useful in making moulds, &c.

The earth of animal bones is calcareous united to the phosphoric acid.

_Of Siliceous Earth._

Siliceous earth seems to be formed by nature from chalk, perhaps by the introduction of some unknown acid, which the vitriolic acid is not able to dislodge. It abounds in most substances which are hard enough to strike fire with steel, as _flint_, _rock crystal_, and most _precious stones_. It is not acted upon by any acid except the fluor and phosphoric, but especially the former: but it is soluble in alkalies; and being then dissolved in water, makes _liquor silicum_, from which the purest siliceous earth may be precipitated by acids. For this purpose about four times the weight of alkali must be made use of. With about equal weights of alkali and siliceous sand is made _glass_, of so great use in admitting light and excluding the weather from our houses, as well as for making various useful utensils. To make glass perfectly colourless, and at the same time more dense, commonly called _flint glass_, manufacturers use a certain proportion of calx of lead and manganese.

Siliceous earth is not affected by the strongest heat, except by means of a burning lens, or dephlogisticated air.

LECTURE XX.

_Of Argillaceous Earth._

Argillaceous earth is found in _clay_, _schistus_, or _slate_, and in _mica_; but the purest is that which is precipitated from a solution of alum by alkalies; for alum consists of the union of vitriolic acid and argillaceous earth.

This species of earth is ductile with water; it then hardens and contracts by heat, so as to be of the greatest use in forming _bricks_, or stones of any required form or size. By means of the property of clay to contract in the fire, Mr. Wedgwood has constructed an excellent thermometer to measure the degrees of extreme heat.

The ductility of clay seems to depend upon some acid, probably the vitriolic, adhering to it; for it loses that property when it is burned into a brick, but recovers it when it has been again dissolved in an acid.

_Of Terra Ponderosa._

_Terra ponderosa_, or _marmor metallicum_, is generally found in two states, viz. united to vitriolic acid, when it is called _calk_, or to fixed air, when it is called _terra ponderosa aerata_.

To obtain it pure from its union with the vitriolic acid, it must be melted with about twice its weight of fixed alkali; which unites with the acid, and forming a saline substance, may be washed out of it. In this state it contains water, and therefore, when exposed to heat, will yield fixed air; whereas the terra ponderosa aerata will not yield fixed air by heat only, but when steam is made to pass over it when red hot. This proves that water is essential to the composition of fixed air.

This stone is distinguishable by its great specific gravity, being four times as heavy as water; but though in this it resembles an _ore_, it has not been found to be metallizable.

_Of Magnesia._

This species of earth is found in _steatites_, or _soap rock_, _Spanish chalk_, _asbestus_, and _Muscovy talck_; but the purest is got by dissolving _Epsom salts_ (which consists of this earth united to the vitriolic acid) and precipitating it by a mild alkali. In this state it becomes united to fixed air, which may be expelled by heat. It is then _calcined_, or _caustic_, but differs from quick-lime by not being soluble in water.

_Asbestus_, which contains much of this kind of earth, is remarkable for not being destructible by heat, though it is sometimes found in flexible fibres, so as to be capable of being woven into cloth.

_Muscovy talck_ is remarkable for the thin and transparent flakes into which it is divisible, and thereby capable of various uses.

There are some other distinct species of earth, particularly one brought from Botany Bay, and another called _Stontiate_, from the place where it was found in Scotland; but they have not as yet been much examined.

All stones formed by nature are compounded, and to distinguish them from one another, and ascertain the parts of which they consist, is the subject of _lithology_, a very extensive branch of knowledge.

All the simple earths are nearly, if not absolutely, _infusible_; but when they are mixed they may all be fused.

LECTURE XXI.

_Of Ores_.

Metallizable earths, commonly called _ores_, when united to phlogiston, make the metals, distinguishable for their specific gravity, their opacity, shining appearance, and fusibility.

All the proper metals are _malleable_, and those which are not so are called _semi-metals_.

The metals again are subdivided into the _perfect_ and _imperfect_. The former, which are _gold_, _silver_, and _platina_, suffer no change by fusion, or the longest continued heat: whereas heat calcines or dissipates the phlogiston of the imperfect metals, which are _mercury_, _lead_, _copper_, _iron_, and _tin_, so that they return to the state of earth; and this earth is always heavier than the metal, though of less specific gravity, having received an addition of weight from water or air: but these earths, or ores, being exposed to heat in contact with substances containing phlogiston, again become metals, and are then said to be _revived_.

The semi-metals are _bismuth_, _zinc_, _nickel_, regulus of _arsenic_, of _cobalt_, of _antimony_, of _manganese_, of _wolfram_, and of _molybdena_.

All metallic substances are crystallizable, and each in a peculiar form, which is discovered by leaving a hole in the bottom of the crucible in which they are melted, and drawing out the stopper, when the mass is beginning to lose its fluidity.

Some of the metals will not unite to others when hot, and others of them will; and such as will unite with others are called _solders_. Thus tin is a solder for lead, and brass, gold, or silver, for iron.

Ores are never found in regular strata, like the different kinds of earth; but in places which have formerly been cavities, running in all directions, with respect to the regular strata, and commonly called _veins_.

Many of the ores in their natural state are said to be _mineralized_ with arsenic or sulphur, those substances being intimately united with the metallic earths.

In order to convert the ores into metals, some of them are first reduced to powder, to wash out the earthy or saline particles. They are then kept in a red heat, which the workmen call _roasting_, in order to drive away the arsenic, or sulphur, which are volatile; and in the last place they are fused in contact with charcoal, or other substances containing phlogiston; and to promote the fusion, lime-stone is frequently mixed with them. When the operation is completed, the unmetallic parts are converted into glass, or _scoria_, which lies on the surface, whereas the metal is found at the bottom.

To discover the quantity of metal in a small piece of ore is called _assaying_.

When metals are fused together, the specific gravity, fusibility, and other properties are changed, and in such a manner as could not be discovered from the properties of the constituent parts.

_Of Gold._

Gold is the heaviest of all metallic bodies except platina. It appears yellow or reddish by reflected light, but green or blue by transmitted light, when it is reduced to thin plates.

Though gold undergoes no change in a common furnace, or burning lens, it may, in part, at least, be calcined by the electric shock.

Gold has the greatest _ductility_, and in wires of equal diameters, it has the greatest _tenacity_, of all the metals. One grain of it may be made to cover 56 square inches; some gold leaf being less than a 200,000th part of an inch thick; and when it is made to cover a silver wire, the gold upon it may not be more than one twelfth part of the thickness of the gold leaf.

This metal is soluble in aqua regia; and being precipitated by a volatile alkali, makes a powder called _aurum fulminans_, which is one fourth heavier than the gold, and explodes with great violence in a heat something greater than that of boiling water.

Tin precipitates gold in the form of a purple powder, called the _powder of Cassius_, from the inventor of it, and is used in enamels, or the glassy coating which is given to metals by heat.

Gold unites with most of the metals, especially with mercury, and these mixtures are called _amalgams_. In gilding, the amalgam is applied to the surface of the metal to be gilded, and the mercury is driven off by heat, leaving the gold attached to the surface.

Gold mixed with iron, makes it harder, for the purpose of cutting instruments.

To separate gold from the imperfect metals, such as copper, &c. it is mixed with lead, and then exposed to a strong heat, which calcines the lead, and with it the imperfect metals, leaving the gold pure. This process is called _cupellation_, from being performed in a small crucible called a _cupell_. When the gold is mixed with silver, three parts more of silver are put to it, and then the silver is dissolved by nitrous acid, leaving the gold pure. This process is called _quartation_, from the gold being one fourth part of the mass.

The fineness of gold is generally estimated by dividing the gold into twenty-four parts, called _carats_. The phrase twenty-three carats fine means that the mass contains twenty-three parts out of twenty-four of pure gold, the remainder being _alloy_, of some baser metal. The fineness of gold may in some measure be discovered by the colour it leaves upon a _touch-stone_, or fine-grained basaltes.

Gold is generally found nearly pure, but mixed with earth, or diffused in fine grains through stones.

LECTURE XXII.

_Of Silver._

Silver is the whitest of all the metals, very ductile, but less so than gold; the thinnest leaves of it being one third thicker than those of gold. It is not calcined in the heat of a common furnace, but partially so by repeated fusion, or a strong burning lens.

Sulphureous fumes unite with silver, and tinge it black. The nitrous acid dissolves it, and will hold more than half its weight of it in solution. When fully saturated, this solution deposits crystals, which are called _lunar nitre_, or _nitre of silver_. When these crystals are melted, and the water they contain driven off, a black substance, called _lapis infernalis_, or _lunar caustic_, is formed. This is used as a cautery in surgery. A strong heat will decompose this lunar nitre, and recover the silver.

Though the nitrous acid dissolves silver the most readily, the marine acid will deprive the nitrous of it, and form a substance called _luna cornea_, because, when it is melted and cold, it becomes a transparent mass something resembling _horn_. From this luna cornea the purest silver may be obtained. The vitriolic acid will likewise deprive the nitrous of the silver contained in it, and form a white powder, not easily soluble in water.

A fulminating silver may be made by the following process: the silver must first be dissolved in pale nitrous acid, then precipitated by lime-water, dried, and exposed to the air three days. It must then be washed in caustic volatile alkali, after which the fluid must be decanted, and the black powder left to dry in the air. The slightest friction will cause this powder to fulminate. It is said, that even a drop of water falling upon it will produce this effect; so that it ought to be made only in very small quantities, and managed with the greatest caution.

Most of the metals precipitate silver. That by mercury may be made to assume the form of a tree, called _arbor Dianae_.

Silver is found native in Peru; and the ores frequently contain sulphur, or arsenic, or both.

_Of Platina._

Platina is a metal lately discovered in the gold mines of Mexico, where it is found in small particles, never exceeding the size of a pea, mixed with ferruginous sand and quartz.

The strongest fire will not melt these grains, though it will make them cohere; but they may be melted by a burning lens, or a blow-pipe supplied with dephlogisticated air.

Pure platina is the heaviest body in nature, its specific gravity exceeding twenty-two. It is very malleable, though considerably harder than gold or silver, and has the property of welding in common with iron. This metal is not affected by exposure to the air, or by any simple acid, though concentrated and hot; but it is dissolved by dephlogisticated marine acid, and by aqua regia, in which a little nitrous air is procured. The solution is brown, and when diluted yellow. This liquor is very corrosive, and tinges animal substances of a blackish brown colour. Platina is precipitated from a solution in aqua regia by sal-ammoniac, as gold is by martial vitriol. Iron is precipitated from this solution by the Prussian alkali. Also most of the metals precipitate platina, but not in its metallic state.

Arsenic facilitates the solution of platina; and by melting it with equal parts of arsenic and vegetable alkali, and then reducing the mass to a powder, it may be made to take any form; and a strong heat will dissipate the arsenic and the alkali, leaving the platina in the shape required, not fusible by any heat in a common furnace.

Platina does not readily combine with gold or silver, and it resists the action of mercury as much as iron; but it mixes well with lead, making it less ductile, and even brittle, according to the proportion of the platina. With copper it forms a compound which takes a beautiful polish, not liable to tarnish, and is therefore used with advantage for mirrors of reflecting telescopes. It unites easily with tin, and also with bismuth, antimony, and zinc.

LECTURE XXIII.

_Of Mercury._