Part 2

15. To ascertain the _chemical properties_ of minerals, one of the most important instruments is the blow─pipe. This is a tube which terminates in a cavity as fine as a small wire, and through which the air is forced, and made to play upon the flame of a candle. The flame is thus concentrated, and directed against small particles of the mineral to be examined, which is placed upon a bit of charcoal in a spoon of platina or silver. The air is forced into the blow─pipe by the mouth of the person using it, or by bellows attached to it for that purpose. Under this operation we have an opportunity of trying the action of other bodies upon minerals at a very high temperature; and the properties which these experiments bring into view enable us, in many cases, to ascertain, not only the nature, but even the component parts, of minerals.

SIMPLE MINERAL SUBSTANCES.

16. As a necessary introduction to the study of minerals, it is requisite to describe, in a brief manner, such simple substances as form their constituent parts. Few of these, it is true, are to be found in a separate, uncombined state; yet that they do exist, and that they are to be obtained from the minerals with which they are united, we have the proof of every day’s experience.

UNCONFINABLE FLUIDS.

17. There are some kinds of unconfinable fluids, the existence even of which is manifested only by their contact with other bodies, or becoming separated from them. They are of a nature too subtile to be collected or confined in our vessels for the purpose of examination, and the investigation of their properties has consequently been attended with peculiar difficulty. Those at present known are _caloric_, _light_, _electricity_, and _magnetism_; but of these the first only is immediately connected with the subjects of our present investigation.

18. _Caloric_.—Every one is acquainted with the different sensations of heat and cold. That matter which produces on our bodies the sensation of _heat_ has the name of _Caloric_; heat being only an effect, of which caloric is the cause. This is extended in a greater or less degree through the whole extent of space, and penetrates into the interior of even the most solid bodies: in so doing it expands the particles of which they are composed, augments their bulk, and diminishes their solidity. The sun is the principal fountain from which the earth is supplied with this fluid; and it passes thence to us at the rate of 12,000,000 of miles per minute. The defect of caloric in any substance occasions the sensation called cold.

Were the world deprived of caloric, every species of organized being would, from that moment, cease to exist. It is the cause of all fluidity: to it every production of the earth has been most essentially indebted, even for its form and structure; and in no respect do the power and goodness of the Almighty appear more conspicuous than in the creation, dispersion, and continuance, of this most subtile and astonishing fluid.

19. All the various substances with which we are acquainted must be considered either as solid or fluid. Every substance is defined to be a _solid_ in which the parts are so united or connected that it requires an external force to separate them. A _fluid_, on the contrary, is a body the parts of which are so loosely connected that they not only yield easily to any force impressed upon them, but also move freely amongst each other; and every fluid is a combination of caloric with some other substance.

20. Fluids are of two kinds: one of these, called _liquids_, have, when at rest, a smooth and distinct surface, and are distinguishable both by the sight and touch; the other, denominated _gas_, or _gaseous fluids_, have the appearance of air, and are not perceptible either to the sight or touch, except under certain circumstances. The latter are principally oxygen (21), azote or nitrogen, and hydrogen (45). We shall at present have occasion to speak only of the first.

GASEOUS FLUIDS.

21. _Oxygen_, like caloric, is a fluid never found in an uncombined state. It forms one of the component parts of the air that we breathe, and of the water we drink; but it approaches nearest to a state of purity in combination with caloric (18), when it has the name of _oxygen gas_. It was formerly called _vital air_, because no breathing animal can live for a moment in any air or gas which has not in it a mixture of oxygen; every kind of combustible burns with great splendour in it, and without it ceases to burn. It unites with a great number of substances, and changes both their appearance and properties in a very remarkable manner. Of the metals it entirely destroys the metallic lustre, and gives them an earthy form and texture. Substances in this state have the name of _oxides_.

Lead, for instance, combined with oxygen becomes the well─known red and heavy substance used by painters, under the name of minium or red lead (239). This, if deprived of its oxygen, loses its red colour, and returns to its former metallic state. Some of the metals are oxidized by merely being exposed to moisture. Thus the rust which is so readily contracted by iron is an oxide of that metal, produced by its attracting oxygen from the air or from water.

ACIDS.

22. It is one of the most remarkable properties of oxygen to impart to most of those bodies called _acids_ their peculiar character of acidity. Oxygen does not itself possess the properties of an acid, nor is it an essential ingredient in all acids, though it is the acidifying principle in the greater number of them.

23. _Acid_ is a word originally synonymous with sour. It has, however, been gradually extended in its signification, and now comprehends all substances possessed of the properties of exciting upon the tongue the sensation called sour; of changing the blue colours of vegetables to red; of uniting with water in almost any proportion; of combining with alkalies (42), metallic oxides, and earths, and of forming with them certain compounds called _salts_.

24. _Sulphuric Acid_, or _Spirit of Vitriol_, as it is commonly called, is a liquid of a somewhat oily consistence, transparent and colourless as water, formed by a combination of oxygen (21) with sulphur (46). Like other acids, it never occurs in nature in a pure state, for it can no sooner be formed than it unites with earths (31), alkalies (42), or metals, and forms, with them, several well─known salts, which have the name of _sulphats_. Thus alabaster (192) and Epsom salts (199) are respectively formed by an union of sulphuric acid with lime and magnesia, and are denominated by chemists sulphat of lime and sulphat of magnesia. In like manner, blue vitriol (209) is sulphat of copper; green vitriol (208), sulphat of iron; and white vitriol (210), sulphat of zinc.

25. _Phosphoric Acid_ is produced by a combination of oxygen (21) with phosphorus (47); and, when obtained in a state of purity, is not a fluid, but a white and flaky substance. This acid, when combined with mineral productions, forms those salts which have the name of _phosphats_. It is very soluble in water; and, in dissolving, makes a hissing noise, similar to that produced by plunging hot iron into water.

26. _Carbonic Acid_ is a compound of oxygen (21) and carbon, or pure charcoal (48): and in a state of gas (20) it forms a constituent part of the atmospheric air. It is also emitted in great abundance from wine, beer, and other liquors, in a state of fermentation, and is sometimes found in the lowest parts of mines, where it is known to the miners by the name of _choke damp_, from the circumstance of its immediately extinguishing flame, and suffocating all animals that are immersed in it. This gas, which was formerly called by chemists _fixed air_, is about twice the weight of common air. In combination with lime it forms chalk, marble, and limestone; and it constitutes part of several other mineral substances, which are thence denominated _carbonats_.

27. _Fluoric Acid_ is a gas of very singular nature, which is held in combination with lime, in the Derbyshire or fluor spar (194); and may be separated from it by pouring sulphuric acid, or spirit of vitriol (24), upon powdered spar, in a leaden vessel called a retort, and applying to it a gentle heat. The salts formed by fluoric acid have the name of _fluats_.

28. The _Boracic_ is a peculiar kind of acid, which, in combination with soda (200), forms the substance that we import from the East Indies under the name of borax (204). When extracted from borax this acid does not assume the form of a fluid, but appears in thin six─sided scales or flakes, of white colour, which adhere slightly together, and feel somewhat greasy in handling. To the taste it is at first sour, then bitterish; and at last it leaves an agreeable sweetness on the palate.

29. _Muriatic Acid_ is a gas formed by the combination of oxygen (21) with some base that is not yet known. It is an invisible and elastic fluid, which, in mechanical properties, resembles common air, and has a pungent and very peculiar smell. This gas unites with alkalies (42), earths (31), and the oxides (21) of metals; and with them forms the compounds called _muriats_, of which common salt, or muriat of soda (202), is one of the principal. The liquid muriatic acid, or muriatic acid gas combined with water, is frequently denominated _spirit of salt_ (202).

30. _Nitric Acid_ is a compound of oxygen and azote, or nitrogen, in the proportion of twenty─five parts, by weight, of the latter to seventy─five of the former. It is one of the constituent parts of nitre, or saltpetre (206); and, in a pure state, is transparent and colourless, like water. By the action of light, however, it soon becomes yellow; and, if exposed to the air, it emits yellow fumes, which even tinge the air of the same colour. To the taste it is extremely acid. It dyes the skin a yellow colour, which is very difficult to be removed; and it is so corrosive as to destroy almost every substance into which it penetrates. If poured upon oils, it sets them on fire. With various bases it forms compounds called _nitrats_. This acid, which hitherto has never otherwise been obtained than mixed with water, is chiefly known in commerce by the name of _aqua fortis_ (206).

EARTHS.

31. The solid contents of the globe are composed of several elementary substances, amongst which have been enumerated no fewer than nine different kinds of earth:

1. Silex. 2. Alumine. 3. Zircon. 4. Glucine. 5. Yttria. 6. Barytes. 7. Strontian. 8. Lime. 9. Magnesia.

These, when freed from foreign admixture, are, for the most part, of white colour, not soluble in water, not combustible, and do not exceed four times the weight of water.

32. The whole of these earths have, till lately, been considered simple and uncombined substances; but, by the discoveries of Sir Humphrey Davy, it has been ascertained that four of them have a metallic basis, and are in fact metallic oxides, or compounds consisting of a metal united with oxygen (21). These, which have the same affinity with their respective bases as rust has to iron, are silex, lime, barytes, and alumine. Until, however, some further light be thrown upon their nature and constitution, they must continue to hold their former situation of simple earths.

33. _Silex_, or _Siliceous Earth_, is the basis of all substances known by the name of quartz and silex (76). In a state of nature it has never been found pure; but, in combination with other substances, it abounds in almost every country of the globe. Common flint (90) contains ninety─seven parts in a hundred of silex: it consequently has given its name to this earth, _silex_ being the Latin word for flint. When purified it is a white powder, the particles of which are harsh to the touch, as if they consisted of very minute grains of sand. It is not quite three times as heavy as water, and has neither taste nor smell. Water will not dissolve it, nor any kind of acid, except fluoric. Sir H. Davy has discovered it to have a metallic basis, to which he has given the name of _silicium_.

34. _Alumine_ is a kind of earth, so called from its forming the basis of alum (197). It is soft, compact, and tenacious; about twice the weight of water, and, when breathed upon, has a smell which is peculiar to all clayey productions. In the fire it shrinks, and becomes so hard as even to yield sparks when struck against steel. It readily absorbs water, and is dissolved by most acids. Some writers state that pure alumine has been discovered in a native state near Halle, in Germany. It is found in a crystallized form, and nearly in a state of purity, in the Oriental ruby and sapphire. The name of _argil_, or clay, has sometimes been applied to it; but, in mineralogy, this name has usually been given to a mixture of alum, quartz, and other substances. Sir H. Davy has obtained from alumine a metallic basis, called _aluminum_.

35. _Zircon_, when freed from those substances with which it is combined, is a white and somewhat rough powder, insipid to the taste, insoluble in water, and about four times as heavy as that fluid. It is found in the two kinds of precious stones called jargoon and hyacinth, and has not hitherto been applied to any useful purpose.

36. _Glucine_ is a kind of earth of peculiar nature, which is found in the emerald and beryl, and, when purified, forms a soft and white powder, without smell, and of sweetish taste. To the last of these qualities it is indebted for its name, which is derived from a Greek word signifying sweet. It is somewhat unctuous to the touch, and about three times as heavy as water. The uses of this earth, whatever they may be, are not known.

37. _Yttria_ is an earth which, among other particulars, differs from glucine by its weight, as it is nearly five times heavier than water. In a natural state it occurs as the basis of a black Swedish mineral, called gadolinite. When cleansed, by chemical process, from all its impurities, it is a fine, white, and inodorous powder.

38. _Barytes_ is a white, porous, and very heavy earth, which can only be obtained pure by chemical process. It is easily reduced to powder, and is soluble in all kinds of acids. To the taste it is harsh and caustic; and, if taken into the stomach, proves an extremely virulent poison. In some respects it agrees with the alkalies (42), particularly in its property of changing blue vegetable colours to green, and in corroding, like them, though with less energy, all kinds of animal substances. From these circumstances it has sometimes been denominated an alkaline earth. Saturated with sulphuric (24) and carbonic acid (26), it constitutes the minerals denominated sulphat and carbonat of barytes (196). It has been discovered to have a metallic base, which is called _barium_.

39. _Strontian_ is an earth which, like barytes, is not found otherwise than in combination with sulphuric and carbonic acids. It occurs in various parts of the world, and, when purified, forms a porous mass of greyish white colour, acrid taste, and somewhat alkaline nature. This earth converts vegetable blue colours to green, but does not act so strongly on animal bodies as barytes, nor is it poisonous, like that substance.

40. _Lime_, the basis of all those substances which are denominated _calcareous_, is only to be obtained in a state of purity by artificial process. Combined with carbonic acid (26) it forms limestone (140), chalk, and marble; all of which are capable of being converted into lime by burning. Lime may also be obtained from oyster and other sea shells. When pure, it is of white colour, and moderately hard substance, though it is easily reducible to powder. Its taste is burning and acrid; and, like the alkalies, it changes vegetable blue colours to green. It has likewise the property of corroding and destroying animal substances. Lime, when pure, absorbs water rapidly, becomes hot, and falls into powder. Even if exposed to the open air it gradually attracts moisture, and assumes a powdery form; soon after which it becomes saturated with carbonic acid (26) from the atmosphere, and is thereby again converted into carbonat of lime (140). It occurs abundantly in almost every country, but always in combination with some acid, carbonic (26), sulphuric (24), boracic (28), fluoric (27), or phosphoric (25). This substance has a metallic basis, which has been denominated _calcium_.

41. _Magnesia_ is a light and perfectly white kind of earth, of soft powdery appearance, without taste or smell, and somewhat more than twice as heavy as water. It is not found in this pure state in nature, but may be prepared from Epsom salt, which consists of magnesia in union with sulphuric acid (24). The slightly acrid taste that is perceptible in the magnesia used in medicine arises from a portion of lime which it contains. This substance does not dissolve in water, but is soluble in every kind of acid. It has the property of changing delicate blue colours to green.

ALKALIES.

42. Alkalies are substances which enter into the composition of several kinds of minerals, and are known by their property of changing the colour of blue vegetable juices to green, and by a peculiarly acrid, caustic, and nauseous taste, which it is impossible to describe, but which, after it has been once experienced, will easily be recollected. Alkalies corrode and dissolve animal substances, and unite with oil and fat in such manner as to form the well known compound called soap. They readily dissolve in water; and, when mixed with acids, form what have been denominated neutral salts.

43. The alkalies at present known are three in number; _potash_ (205), _soda_ (200), and _ammonia_ (207). Of these the two former, although till lately they have been considered simple substances, have been shown by Sir H. Davy to have metallic bases.

SIMPLE COMBUSTIBLES.

44. By this term we are to understand all those mineral substances, capable of combustion, which have not been discovered to consist of more than a single component part. They are four in number; _hydrogen_, _sulphur_, _phosphorus_, and _carbon_.

45. _Hydrogen_, as its name imports, is a principal constituent part of water; for, singular as it may appear, that well─known fluid is formed by a combination of two species of air or gas, called hydrogen and oxygen (21), and in the proportion of about fifteen parts of the former and eighty─five parts of the latter. This gas had formerly the denomination of _inflammable air_, and has long been known in mines under the name of _fire─damp_. It is about twelve times lighter than atmospheric air. When pure it soon destroys such animals, and extinguishes all such flaming substances, as are immersed in it. Mixed with atmospheric air, it explodes with great violence on the application of any ignited body.

46. _Sulphur_ is a simple combustible substance, of yellow colour, which is found pure, or native, in several parts of the world, and is sufficiently familiar to us under the name of _brimstone_ (211). It strongly attracts oxygen (21), and is thereby converted into sulphuric acid (24). It frequently occurs in combination with mineral substances, such as arsenic, antimony, copper, and other metallic ores.

47. _Phosphorus_ is a combustible substance which, when pure, somewhat resembles bees’─wax both in colour and consistence; and, when exposed to the air under the usual temperature of our atmosphere, is luminous in the dark, and has a smell somewhat resembling that of garlic. It is so combustible that, when melted, it should be kept under water, as it cannot be exposed to the air during this process without great risk of catching fire. This substance is not known in a native state; and the whole of what is used in philosophy and commerce is obtained by different artificial processes. In union with oxygen (21) it becomes converted into an acid, called _phosphoric acid_ (25), and, under this form, in conjunction with lime, it constitutes the bones of men and animals. The greater part of the phosphorus of the shops is obtained from bones.

48. _Carbon_ is a name given to the pure inflammable part of charcoal. It is abundantly diffused throughout nature, for it enters into the composition of several minerals, and of all vegetable and animal bodies. The purest form under which carbon is known to exist is in the diamond (50). It may, however, be obtained sufficiently pure, for all common purposes, by burning a piece of wood, covered with sand, in a vessel called a crucible. In combination with oxygen (21) it forms carbonic acid (26). Carbon is a chief component part of pit─coal (217), petroleum (213), and other bituminous substances.

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CLASS I.—STONES.

ORDER I.—EARTHY STONES.

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_I. HARD: those which scratch Glass._

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49. OF GEMS IN GENERAL.

Gems, or precious stones, as they are frequently called, are, for the most part, transparent, and have a vitreous or glassy appearance. Their different colours are occasioned by metallic oxides (21) of various kinds, with which they are impregnated. Some writers have classed them by their colours, but this is a very uncertain mode, as different gems have not unfrequently the same colour; and, in many cases, the same gems are of different colours. The usual distinction of gems into Oriental and Occidental is also liable to error, as the best gems, from whatever part of the world they are brought, are always called Oriental. The most estimable of all the kinds are the diamond (50), ruby (54), emerald (67), and sapphire (53); and stones a grain in weight, and equal in quality, are valued in the following proportions, at 8_l._ per carat for diamonds, 4_l._ for rubies, and 3_l._ for each of the others. The amethyst (79), topaz (61), and aqua─marine (61), are considered of nearly equal value with each other; and the garnet (70) is the cheapest of precious stones.

The ancients engraved upon several kinds of gems; but they appear to have been ignorant of the art of cutting the diamond, the ruby, and the sapphire, which were too hard for them to operate upon. The emerald and the noble opal (102) were too highly esteemed as precious stones to have often found their way into the hands of engravers. It has been asserted that the ancients did not use the topaz for engraving; but there is extant a beautiful _intaglio_, representing an Indian Bacchus, which is said to be a topaz. The garnet was often engraved upon: and there are many master─pieces of the art in calcedony (91) and carnelian (93.) Onyx and sardonyx (92) were employed for that species of engraving in relief called _cameos_; and, in many instances, it is pleasing to observe with what dexterity the ancient artists availed themselves of the different colours in the alternate zones to express the different parts and shades of their figures.

Most of the gems may be imitated by artificial preparations of glass, coloured by different metallic substances; and it is not easy, by mere inspection, to distinguish the better kinds of factitious stones from real gems. They are, however, discoverable by a deficiency of lustre, and being so soft as, even in the most perfect kinds, to yield to the point of a steel instrument.