Heads of Lectures on a Course of Experimental Philosophy: Particularly Including Chemistry Part 7

LECTURE XVII.

_Of Liquid Inflammable Substances._

Of liquid inflammable substances the princ.i.p.al 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 pa.s.s 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 insp.i.s.sated.

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 a.s.sist 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 quant.i.ty of oil and water be put into a gla.s.s 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 _b.u.t.ter_, or _fat_, which is easily congealed, owing to the quant.i.ty 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 princ.i.p.al component parts of all these substances are an oil and an acid. But all fossil oil is probably of vegetable or animal origin, from ma.s.ses 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 princ.i.p.al 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 pa.s.sing from a fluid into a solid state their component parts a.s.sume 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 princ.i.p.al 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 sh.e.l.ls 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 sh.e.l.ls formed in the sea, in some pristine state of the earth.

The calcareous earth which is found in sh.e.l.ls, 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 ma.s.s, 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.