ON EARTHS AND STONES

Tutor—George—Harry.

Harry.I wonder what all this heap of stones is for?

George.I can tell you—it is for the lime-kiln; do n’t you see it just by?

Har.O yes, I do. But what is to be done to them there?

Geo.Why, they are to be burnt into lime; do n’t you know that?

Har.But what is lime, and what are its uses?

Geo.I can tell you one; they lay it on the fields for manure. Do n’t you remember we saw a number of little heaps of it, that we took for sheep at a distance, and wondered they did not move? However, I believe we had better ask our tutor about it. Will you please, sir, to tell us something about lime?

Tutor.Willingly. But suppose, as we talked about all sorts of metals some time ago, I should now give you a lecture about stones and earths of all kinds, which are equally valuable, and much more common than metals.

Geo.Pray, do, sir.

Har.I shall be very glad to hear it.

Tut.Well, then. In the first place, the ground we tread upon, to as great a depth as it has been dug, consists for the most part of matter of various appearance and hardness, called by the general name ofearths. In common language, indeed, only the soft and powdery substances are so named, while the hard and solid are calledstoneorrock; but chymists use the same term for all; as, in fact, earth is only crumbled stone, and stone only consolidated earth.

Har.What!—has the mould of my garden ever been stone?

Tut.The black earth or mould which covers the surface wherever plants grow, consists mostly of parts of rotted vegetables, such as stalks, leaves, and roots, mixed with sand or loose clay; but this only reaches a little way; and beneath it you always come to a bed of gravel, or clay, or stone of some kind. Now these earths and stones are distinguished into several species, but principally into three, the properties of which make them useful to man for very different purposes, and are, therefore, verywell worth knowing. As you began with asking me about lime, I shall first mention that class of earths from which it is obtained. These have derived their name ofcalcareousfrom this very circumstance,calxbeing lime, in Latin; and lime is got from them all in the same way, by burning them in a strong fire. There are many kinds of calcareous earths. One of them ismarble; you know what that is?

Geo.O yes! Our parlour chimney-piece and hearth are marble.

Har.And so are the monuments in the church.

Tut.True. There are various kinds of it: white, black, yellow, gray, mottled and veined with different colours; but all of them are hard and heavy stones, admitting a fine polish, on which account they are much used in ornamental works.

Geo.I think statues are made of it?

Tut.Yes; and where it is plentiful, columns, and porticoes, and sometimes whole buildings. Marble is the luxury of architecture.

Har.Where does marble come from?

Tut.From a great many countries. Great Britain produces some, but mostly of inferior kinds. What we use chiefly comes from Italy. The Greek islands yield some fine sorts. That of Paros is of ancient fame for whiteness and purity, and the finest antique statues have been made of Parian marble.

Har.I suppose black marble will not burn into white lime?

Tut.Yes, it will. A violent heat will expel most of the colouring matter of marbles, and make them white.Chalkis another kind of calcareous earth. This is of a much softer consistence than marble; being easily cut with a knife, and marking things on which it is rubbed. It is found in great beds in the earth; and in some parts of England whole hills are composed of it.

Geo.Are chalk and whiting the same?

Tut.Whiting is made of the finer and purer particles of chalk washed out from the rest, and then dried in lumps. This you know is quite soft and crumbly. There are, besides, a great variety of stones in the earth harder than chalk, but softer than marble, which will burn to lime, and are therefore calledlime-stones. These differ much in colour and other properties, and accordingly furnish lime of different qualities. Whole ridges of mountains in various parts are composed of lime-stone, and it is found plentifully in most of the hilly counties of England, to the great advantage of the inhabitants.

Geo.Will not oyster-shells burn into lime? I think I have heard of oyster-shell lime.

Tut.They will, and this is another source of calcareous earth. The shells of all animals, both land and sea, as oysters, mussels, cockles, crabs, lobsters, snails, and the like, and also egg-shells of all kinds, consist of this earth; and so does coral, which is formed by insects under the sea, and is very abundant in some countries. Vast quantities of shells are often found deep in the earth, in the midst of chalk and lime-stone beds; whence some have supposed that all calcareous earth is originally an animal production.

Har.But where could animals enough ever have lived to make mountains of their shells?

Tut.That, indeed, I cannot answer. But there are sufficient proofs that our world must long have existed in a very different state from the present. Well—but besides these purer calcareous earths, it is very frequently found mingled in different proportions with other earths. Thusmarl, which is so much used in manuring land, and of which there are a great many kinds, consists of calcareous earth, united with clay and sand; and the more of this earth it contains, the richer manure it generally makes.

Geo.Is there any way of discovering it when it is mixed in this manner with other things?

Tut.Yes—there is an easy and sure method of discovering the smallest portion of it. All the varieties of calcareous earth that I have mentioned have the property of dissolving in acids, and effervescing with them; that is, they bubble and hiss when acids are poured upon them. You may readily try this at any time with a piece of chalk or an oyster-shell.

Geo.I will pour some vinegar upon an oyster-shell as soon as I get home. But now I think of it, I have often done so in eating oysters, and I never observed it to hiss or bubble.

Tut.Vinegar is not an acid strong enough to act upon a thing so solid as a shell. But sulphuric and muriatic acids will do it at once; and persons who examine the nature of fossils always travel with a bottle of one of these acids, by way of a test of calcareous earth. Your vinegar will answer with chalk or whiting. This property of dissolving in acids, and what is called neutralizing them, or taking away their sourness, has caused many of the calcareous earths to be used in medicine. You know that sometimes our food turns very sour upon the stomach, and occasions the pain called heart-burn, and other uneasy symptoms. In these cases itis common to give chalk or powdered shells, or other things of this kind, which afford relief, by neutralizing the acid.

Geo.I suppose, then,magnesiais something of this sort, for I have often seen it given to my little sister, when they said her stomach was out of order?

Tut.It is; but though magnesia has some properties in common with calcareous earths, it possesses others that are peculiar to itself.

Geo.Pray, what are the other uses of these earths?

Tut.Such of them as are hard stone, as the marbles and many of the lime-stones, are used for the same purposes as other stones. But their great use is in the form of lime, which is a substance of many curious properties that I will now explain to you. When fresh burnt it is calledquicklime, on account of the heat and life, as it were, which it possesses. Have you ever seen a lump put into water?

Geo.Yes, I have.

Tut.Were you not much surprised to see it swell and crack to pieces, with a hissing noise and a great smoke and heat?

Geo.I was, indeed. But what is the cause of this—how can cold water occasion so much heat?

Tut.I will tell you. The strong heat to which calcareous earth is exposed in making it lime expels all the water it contained, (for all earths, as well as almost everything else, naturally contain water,) and also a quantity of a peculiar kind of air which was united with it. If water be now added to this quicklime, it is drunk in again with such rapidity, as to crack and break the lime to pieces. At the same time a great heat is occasioned by the water combining with the lime, and this makes itself sensible by its effects, burning all the things that it touches, and turning part of the water to steam. This operation is called slacking of lime. The water in which lime is slacked dissolves a part of it, and acquires a very pungent harsh taste: this is used in medicine under the name of lime-water. If instead of soaking quicklime in water, it is exposed for sometime to the air, it attracts moisture slowly, and by degrees fails to powder, without much heat or disturbance. But whether lime be slacked in water or air, it does not at first return to the state in which it was before, since it still remains deprived of its air, and on that account is still pungent and caustic. At length, however, it recovers this also from the atmosphere, and is then mild calcareous earth as at first. Now it is upon some of these circumstances that the utility of lime depends. In the first place, itsburning and corroding quality makes it useful to the tanner, in loosening all the hair from the hides, and destroying the flesh and fat that adhered to them. And so in various other trades it is used as a great cleanser and purifier.

Har.I have a thought come into my head. When it is laid upon the ground, I suppose its use must be to burn up the weeds?

Tut.True—that is part of its use.

Geo.But it must burn up the good grass and corn too?

Tut.Properly objected. But the case is, that the farmer does not sow his seeds till the lime is rendered mild by exposure to the air and weather, and is well mixed with the soil. And even then it is reckoned a hot and forcing manure, chiefly fit for cold and wet lands. The principal use of lime, however, is as an ingredient inmortar. This, you know, is the cement by which bricks and stones are held together in building. It is made of fresh slacked lime and a proportion of sand well mixed together; and, when used for plastering walls, some chopped hair is put into it. The lime binds with the other ingredients; and in length of time, the mortar, if well made, becomes as hard, or harder, than stone itself.

Geo.I have heard of the mortar in very old buildings being harder and stronger than any made at present.

Tut.That is only on account of its age. Burning lime and making mortar are as well understood now as ever: but in order to have it excellent, the lime should be of a good quality, and thoroughly burnt. Some sorts of lime have the property of making mortar which will harden under water, whence it is much valued for bridges, locks, wharfs, and the like.

Geo.Pray, is not plaster of Paris a kind of lime? I know it will become hard by only mixing water with it, for I have used it to make casts of.

Tut.The powder you call plaster of Paris is made of an earth namedgypsum, of which there are several kinds.Alabasteris a stone of this sort, and hard enough to be used like marble. The gypseous earths are of the calcareous kind, but they have naturally a portion of acid united with them, whence they will not effervesce on having acid poured on them. But they are distinguished by the property, that after being calcined or burnt in the fire, and reduced to powder, they will set into a solid body by the addition of water alone. This makes them very useful for ornamental plasters, that are to receive a form or impression, such as the stucco for the ceiling of rooms.

Well—we have said enough about calcareous earths; now to another class, theargillaceous.

Geo.I think I know what those are.ArgillaisLatinforclay.

Tut.True; and they are also calledclayeyearths. In general, these earths are of a soft texture and a sort of greasy feel; but they are peculiarly distinguished by the property of becoming sticky on being tempered with water, so that they may be drawn out and worked into form like a paste. Have you ever, when you were a little boy, made a clay-house?

Geo.Yes, I have.

Tut.Then you well know the manner in which clay is tempered, and worked for this purpose?

Har.Yes—and I remember helping to make little pots and mugs of clay.

Tut.Then you imitated the potter’s trade; for all utensils of earthenware are made of clays either pure or mixed. This is one of the oldest arts among mankind, and one of the most useful. They furnish materials for building, too; for bricks and tiles are made of these earths. But in order to be fit for these purposes, it is necessary that clay should not only be soft and ductile while it is forming, but capable of being hardened afterward; and this it is, by the assistance of fire. Pottery-ware and bricks are burnt with a strong heat in kilns, by which they acquire a hardness equal to that of the hardest stone.

Geo.I think I have heard of bricks being baked by the sun’s heat alone in very hot countries.

Tut.True; and they may serve for building in climates where rain scarcely ever falls; but heavy showers would wash them away. Fire seems to change the nature of clays; for after they have undergone its operation, they become incapable of returning of themselves to a soft and ductile state. You might steep brick-dust or pounded pots in water ever so long without making it hold together in the least.

Geo.I suppose there are many kinds of clays?

Tut.There are. Argillaceous earths differ greatly from each other in colour, purity, and other qualities. Some are perfectly white, as that of which tobacco-pipes are made. Others are blue, brown, yellow, and in short of all hues, which they owe to mixtures of decaying vegetable substances or metals. Those which burn red contain a portion of iron. No clays are found perfectly pure; but they are mixed with more or less of other earths. The common brick-clays contain a large proportion of sand,which often makes them crumbly and perishable. In general, the finest earthenware is made of the purest and whitest clays; but other matters are mixed in order to harden and strengthen them. Thusporcelainorchinais made with a clayey earth mixed with a stone of vitrifiable nature, that is, which may be melted into glass; and the fine pottery calledqueen’s wareis a mixture of tobacco-pipe clay, and flints burnt and powdered. Common stonewareis a coarse mixture of this sort. Some species of pottery are made with mixtures of burnt and unburnt clay; the former I told you before, being incapable of becoming soft again with water like a natural clay.

Har.Are clays of no other use than to make pottery of?

Tut.Yes, the richest soils are those which have a proportion of clay; and marl, which I have already mentioned as a manure, generally contains a good deal of it. Then clay has the property of absorbing oil or grease, whence some kinds of it are used like soap for cleaning clothes. The substance calledfullers’ earthis a mixed earth of the argillaceous kind; and its use in taking out the oil which naturally adheres to wool is so great, that it has been one cause of the superiority of our woollen cloths.

Har.Then I suppose it is found in England?

Tut.Yes. There are pits of the best kind of it near Woburn in Bedfordshire, and Nutfield in Surrey, England. The different kinds of slate, too, are stones of the argillaceous class; and very useful ones, for covering houses, and other purposes.

Har.Are writing slates like the slates used for covering houses?

Tut.Yes; but their superior blackness and smoothness make them show better the marks of the pencil.

Geo.You have mentioned something of sand and flints, but you have not told us what sort of earths they are.

Tut.I reserved that till I spoke of the third great class of earths. This is thesiliceousclass, so named fromsilex, which is Latin for a flint-stone. They have also been calledvitrifiableearths, because they are the principal ingredient in glass, named in Latinvitrum.

Geo.I have heard of flint-glass.

Tut.Yes—but neither flint, nor any other of the kind, will make glass, even by the strongest heat, without some addition; but this we will speak of by-and-by. I shall now tell you the principal properties of these earths. They are all very hard, and will strike fire with steel, when in a masslarge enough for the stroke. They mostly run into particular shapes, with sharp angles and points, and have a certain degree of transparency, which has made them also be calledcrystallineearths. They do not in the least soften with water, like clays; nor are they affected by acids, nor do they burn to lime, like the calcareous earths. As to the different kinds of them,flinthas already been mentioned. It is a very common production in some parts, and is generally met with in pebbles, or round lumps forming pebbles, in gravel-beds, and often almost entirely covering the surface of ploughed fields.

Har.But do they not hinder the corn from growing?

Tut.The corn, to be sure, cannot take root upon them, but I believe it has been found that the protection they afford to the young plants which grow under them is more than equal to the harm they do by taking up room. Flints are also frequently found imbedded in chalk under the ground. Those used in the Staffordshire potteries chiefly come from the chalk-pits near Gravesend. So much for flints. You have seen white pebbles, which are semi-transparent, and when broken resemble white sugar-candy. They are common on the seashore, and beds of rivers.

Har.O, yes. We call them fire-stones. When they are rubbed together in the dark they send out great flashes of light, and have a particular smell.

Tut.True. The proper name of these isquartz. It is found in large quantities in the earth, and the ores of metals are often imbedded in it. Sometimes it is perfectly transparent, and then it is calledcrystal. Some of these crystals shoot into exact mathematical figures; and because many salts do the same, and are also transparent, they are called thecrystalsof such or such a salt.

Geo.Is not fine glass called crystal, too?

Tut.It is called so by way of simile; thus we say of a thing, “It is as clear as a crystal.” But the only true crystal is an earth of the kind I have been describing. Well, now we come tosand; for this is properly only quartz in a powdery state. If you examine the grains of sand singly, or look at them with a magnifying glass, you will find them all either entirely or partly transparent; and in some of the white shining sands the grains are all little bright crystals.

Har.But most sand is broken or yellowish.

Tut.That is owing to some mixture generally of the metallic kind. Ibelieve I once told you that all sands were supposed to contain a small portion of gold. It is more certain that many of them contain iron.

Geo.But what could have brought this quartz and crystal into powder, so as to have produced all the sand in the world?

Tut.That is not very easy to determine. On the seashore, however, the incessant rolling of the pebbles by the waves is enough in time to grind them to powder; and there is reason to believe that the greatest part of what is now dry land was once sea, which may account for the vast beds of sand met with inland.

Geo.I have seen some stone so soft that one might crumble it between one’s fingers, and then it seemed to turn to sand.

Tut.There are several of this kind, more or less solid, which are chiefly composed of sand conglutinated by some natural cement. Such are calledsandstone, orfreestone, and are used for various purposes, in building, making grindstones, and the like, according to their hardness.

Har.Pray, what are the common pebbles that the streets are paved with? I am sure they strike fire enough with horses’ shoes.

Tut.They are stones of the siliceous kind, either pure or mixed with other earths. One of the hardest and best for this purpose is calledgranite, which is of various kinds and colours, but always consists of grains of different siliceous stones cemented together. The streets of London are paved with granite brought from Scotland. In some other stones these bits of different earths dispersed through the cement are so large as to look like plums in a pudding; whence they have obtained the name ofpudding-stones.

Geo.I think there is a kind of stones that you have not yet mentioned—precious stones.

Tut.These, too, are mostly siliceous; but some even of the hardest and most valuable are argillaceous in their nature, though possessing none of the external properties of clay. The opaque and half-transparent precious stones, such as jasper, agate, cornelian, and lapis lazuli, are engraved upon for seal-stones; the more beautiful and transparent ones, as ruby, emerald, sapphire, topaz, which go by the name of gems, are generally only cut and polished, and worn in rings, ear-rings, necklaces, and the like.

Geo.Diamond, no doubt, is one of them.

Har.So it has commonly been reckoned, and the purest of all; but late experiments have shown, that though it is the hardest body in nature itmay be totally dispersed into vapour by a strong fire, so that mineralogists will now hardly allow it to be a stone at all, but class it among inflammable substances. The precious stones abovementioned owe their colours chiefly to some metallic mixture. They are in general extremely hard, so as to cut glass, and one another; but diamonds will cut all the rest.

Geo.But are they not exceedingly rare?

Tut.Yes; and in this rarity consists the greatest part of their value. They are, indeed, beautiful objects; but the figure they make in proportion to their expense is so very small, that their high price may be reckoned one of the principal follies among mankind. What proportion can there possibly be between the real worth of a glittering stone as big as a hazelnut, and a magnificent house and gardens, or a large tract of country covered with noble woods and rich meadows and cornfields? And as to the mere glitter, a large lustre of cut glass has an infinitely greater effect on the eye than all the jewels of a foreign prince.

Geo.Will you please to tell us how glass is made?

Tut.Willingly. The base of it is, as I said before, some earth of the siliceous class. Those commonly used are flint and sand. Flint is first burnt or calcined, which makes it quite white, like enamel; and it is then powdered. This is the material sometimes used for some very white glasses; but sand is that commonly preferred, as being already in a powdery form. The white crystalline sands are used for fine glass; the brown or yellow for the common sort. As these earths will not melt of themselves, the addition in making glass is somewhat that promotes their fusion. Various things will do this; but what is generally used is an alkaline salt, obtained from the ashes of burnt vegetables. Of this there are several kinds, as potash, pearlash, barilla, and kelp. The salt is mixed with the sand in a certain proportion, and the mixture then exposed in earthen pots to a violent heat, till it is thoroughly melted. The mass is then cooled till it is nearly of the consistence of dough, and in this state it is fashioned by blowing and the use of shears and other instruments. You must see this done some time, for it is one of the most curious and pleasing of all manufactures; and it is not possible to form an idea of the ease and dexterity with which glass is wrought, without an actual view.

Har.I should like very much to see it, indeed.

Geo.Where is glass made in this country?

Tut.In many places. Some of the finest in London, but the coarserkinds generally where coals are cheap; as at Newcastle and its neighbourhood, in Lancashire, at Stourbridge, Bristol, and in South Wales. I should have told you, however, that in our finest and most brilliant glass, a quantity of the oxide of lead is put, which vitrifies with the other ingredients, and gives the glass more firmness and density. The blue, yellow, and red glasses are coloured with the oxides of other metals. As to the common green glass, it is made with an alkali that has a good deal of calcareous earth remaining with the ashes of the plant. But to understand all the different circumstances of glassmaking, one must have a thorough knowledge of chymistry.

Geo.I think making of glass is one of the finest inventions of human skill.

Tut.It is perhaps not of that capital importance that some other arts possess; but it has been a great addition to the comfort and pleasure of life in many ways. Nothing makes such clean and agreeable vessels as glass, which has the quality of not being corroded by any kind of liquor, as well as that of showing its contents by its transparency. Hence it is greatly preferable to the most precious metals for drinking out of; and for the same reasons it is preferred to every other material for chymical utensils, where the heat to be employed is not strong enough to melt it.

Har.Then glass windows.

Tut.Ay; that is a very material comfort in a climate like ours, where we so often wish to let in the light, and keep out the cold wind and rain. What could be more gloomy than to sit in the dark, or with no other light than came in through small holes covered with oiled paper or bladder unable to see anything passing without doors! Yet this must have been the case with the most sumptuous palaces before the invention of window-glass, which was a good deal later than that of bottles and drinking-glasses.

Har.I think looking-glasses are very beautiful.

Tut.They are, indeed, very elegant pieces of furniture, and very costly too. The art of casting glass into large plates, big enough to reach almost from the bottom to the top of a room, is but lately introduced into this country from France. But the most splendid and brilliant manner of employing glass is in lustres and chandeliers, hung around with drops cut so as to reflect the light with all the colours of the rainbow. Some of the shops in London, filled with these articles, appear to realize all the wonders of an enchanted palace in the Arabian Nights’ Entertainments

Geo.But are not spectacles and spying-glasses more useful than all these?

Tut.I did not mean to pass them over, I assure you. By the curious invention of optical glasses of various kinds, not only the natural defects of the sight have been remedied, and old age has been in some measure lightened of one of its calamities, but the sense of seeing has been wonderfully extended. The telescope has brought distant objects within our view, while the microscope has given us a clear survey of near objects too minute for our unassisted eyes. By means of both, some of the brightest discoveries of the modern times have been made; so that glass has proved not less admirable in promoting science than in contributing to splendour and convenience. Well—I don’t know that I have anything more at present to say relative to the class of earths. We have gone through the principal circumstances belonging to their three great divisions, thecalcareous,argillaceous, andsiliceous. You will remember, however, that most of the earths and stones offered by nature are not in any one of these kinds perfectly pure, but contain a mixture of one or both the others. There is not a pebble that you can pick up, which would not exercise the skill of a mineralogist fully to ascertain its properties, and the materials of its composition. So inexhaustible is nature!

The Native Village, p.281.EVENING XXIII.

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