might justly despise; but its free spirit would instruct them in the rights of man; and some institutions of public and private life were adopted from the French. The correspondence of Constantinople and Italy diffused the knowledge of the Latin tongue; and several of the fathers and classics were at length honored with a Greek version. But the national and religious prejudices of the Orientals were inflamed by persecution; and the reign of the Latins confirmed the separation of the two churches. The principle of the erusades was a savage fanaticism; and the most important effects were analagous to the cause. Each pilgrim was ambitious to return with his sacred spoils, the relics of Greece and Palestine; and each relic was preceded and followed by a train of miracles and visions. The belief of the Catholics was corrupted by new legends, their practice by new superstitions; and the establishment of the inquisition, the mendicant orders of monks and friars, the last abuse of indulgences, and the final progress of idolatry, flowed from the baleful fountain of the Holy War. The active spirit of the Latins preyed on the vitals of their reason and religion; and if the ninth and tenth centuries were the times of darkness, the thirteenth and fourteenth were the ages of absurdity and fable. In the profession of Christianity, in the cultivation of a fertile land, the northern conquerors of the Roman empire insensibly mingled with the provincials, and rekindled the embers of the arts of antiquity. Their settlements about the age of Charlemagne had acquired some degree of order and stability, when they were overwhelmed by new swarms of invaders, the Normans, Saracens, and Hungarians, who replunged the western countries of Europe into their former state of anarchy and barbarism. About❘ the eleventh century, the second tempest had subsided by the expulsion or conversion of the enemies of Christendom; the tide of civilization, which had so long ebbed, began to flow with a steady and accelerated course, and a fairer prospect was opened to the hopes and efforts of the rising generations. Great was the increase and rapid the progress during the two hundred years of the crusades; and some philosophers have applauded the propitious influence of these holy wars, which appear to me to have checked rather than forwarded the maturity of Europe. The lives and labors of millions, which were buried in the East, would have been more profitably employed in the improvement of their native country; the accumulated stock of industry and wealth would have overflowed in navigation and trade, and the Latins would have been enriched and enlightened by a pure and friendly correspondence with the climates of the East. In one respect I can, indeed, perceive the accidental operation of the crusades, not so much in producing a benefit as in removing an evil. The larger portion of the inhabitants of Europe was chained to the soil, without freedom, or property, or knowledge; and the two orders of ecclesiastics and nobles, whose numbers were comparatively small, alone deserved the name of citizens and men. This oppressive system was supported by the arts of the clergy and the swords of the barons. The authority of the priests operated in the darker ages as a salutary antidote; they prevented the total extinction of letters, mitigated the fierceness of the times, sheltered the poor and defenceless, and preserved or revived the peace and order of civil society. But the independence, rapine, and discord of the feudal lords were unmixed with any semblance of good; and every hope of industry and improvement was crushed by the iron weight of the martial aristocracy. Among the causes that undermined that gothic edifice, a conspicuous place must be allowed to the crusades. The estates of the barons were dissipated, and their race was often extinguished, in these costly and perilous expeditions. Their poverty extorted from their pride those charters of freedom which unlocked the fetters of the slave, secured the farm of the peasant, and the shop of the

artificer, and gradually restored a substance and a soul to the most numerous and useful part of the community. The conflagration which destroyed the tall and barren trees of the forest, gave air and scope to the vegetation of the smaller and nutritive plants of the soil.*

The old order changeth, yielding place to new,
And God fulfills himself in many ways,

Lest one good custom should corrupt the world.
If thou shouldst never see my face again,

Pray for my soul. More things are wrought by prayer
Than this world dreams of. Wherefore let thy voice
Rise like a fountain for me night and day.
For what are men better than sheep and goats
That nourish a blind life within the brain,

If, knowing God, they lift not hands of prayer,
Both for themselves and those who call them friend?
For so the whole round earth is every way
Bound by gold chains about the feet of God.
But now Farewell!

-Tennyson: "The Passing of Arthur."

*Gibbon's Decline and Fall of the Roman Empire.

CHEMISTRY. III.

SILICON, BORON, ARSENIC.-Just as certain letters are employed to spell certain words, and as a fixed number of letters constitute the alphabet, so in Chemistry do certain letters indicate certain elements, and always represent fixed weights of those elements. According to their behavior toward Hydrogen, we can arrange the elements in classes.

Those which unite with Hydrogen, atom for atom, are called monads. Others, which unite with two atoms of Hydrogen, are called dyads, from the Greek word signifying two. Again, others are called triads, and displace, or unite with, three atoms of Hydrogen. Yet others are called tetrads, and for similar reasons, because they displace, or unite with, four atoms of Hydrogen.

To take illustrations. Chlorine unites with hydrogen to form hydrogen chloride, HCI; it is therefore a monad. Oxygen unites with hydrogen to form hydrogen oxide, H2O; it is therefore a dyad. Nitrogen with hydrogen forms ammonia, H,N; it is a triad. Carbon unites with hydrogen to form marsh gas, H,C; carbon is therefore a tetrad.

SILICON.-The element Silicon* is not found native, nor is it of any value in an uncombined state. Nevertheless, in combination with oxygen, it constitutes the principal part of the earth's crust: as silicic acid it is indeed a well-known mineral.

In properties, silicon closely resembles carbon and belongs to the same group of elements. If heated strongly in oxygen, it burns with magnificent light to silicic acid, just as carbon burns to carbonic acid.

Silicic acid is found in the pure state, and is met with as "rock-crystal," in perfectly colorless and transparent, beautifully crystallized, six-sided prisms. The finest crystals are cut into ornaments, or are employed as substitutes for glassin spectacles, and other optical instruments. So used, they are termed pebbles, and they possess an advantage over glass in their extreme hardness, rendering them less liable to be scratched. The finest specimens of rock-crystal are found in the mountains of Switzerland, Ceylon, Madagascar, and Brazil. A purple variety is known as "amethyst." Brown and yellow rock crystals, of great beauty and value as stones, are found in the mountain of Cairngorm in Scotland. The precious "opal" is but a combination of silicic acid with water. All the varieties of beautiful stones known as Agate, Blood-stone, Flint, Carnelian, Cat's-eye, Onyx,

* Symbol Si, Tetrad.

Many of the metals are capable of combination with others to form alloys; some of these are possessed of much beauty, others of great importance in the useful and fine arts. Copper, for instance, is not suitable for castings; but, combined with zinc, it forms the alloy brass, and with tin, bronze. Steel, a carbide of iron, is a compound of carbon with iron. A combination of mercury with other metals is not called an alloy, but an amalgam.

Some of the metals, as iron and platinum, possess the valuable property of softening before fusion, and in this state several pieces may be united by pressure, a mode of union known as welding.

The compounds of oxygen with the non-metallic elements have acid properties; they redden litmus when soluble in water, and generally unite with hydrogen oxide to form a salt of hydrogen.

Oxygen unites with the metals, and forms metallic oxides or bases, with properties the very opposite to those of acids. When soluble in water, they turn red litmus- paper blue, and they unite with acids to form salts.

Oxygen unites with the metals in different proportions, and forms different classes of basic oxides. When only one basic oxide is known, it is simply called by the name of the metal, as lead oxide, silver oxide, potassium oxide, etc., and the salts are known as those of lead, silver, and potassium. But when a metal forms two basic oxides, the one containing least oxygen is known by the affix ous, and the other Containing most, by the affix ic. Thus we have ferrous and ferric oxides, and ferrous and ferric salts.

Sulphur unites with the metals, and forms sulphides. Most of the oxides have corresponding sulphides, and the same distinctions are made. We have but one sulphide of lead, silver and potassium, but there are two sulphides of iron, distinguished as ferrous sulphide, and ferric sulphide. A metallic compound from which the metal is usually extracted, is called an ore.

If

Metallic ores do not generally compose large beds or extensive strata in the crust of our globe, but are usually found in clefts, rents, or fissures called veins. The process of obtaining the ores from these veins is called mining-a term also applied in the getting of coal, salt, etc. The mode of proceeding varies. The mining operations are the simplest when the vein is in strata, hills, rocks, or mountains. the vein be exposed at the surface of the ground, the mineral is simply dug out, and the excavation thus made, serves as a passage to the interior of the mountain in following the vein. When the vein does not appear externally, or when it takes a new direction after being followed for some distance, access to it is obtained by adits or levels (horizontal galleries dug from the sides of the hill), till the vein is reached. Similar galleries are also sometimes constructed to carry off the water which drains through the higher parts of the mountain, and which would otherwise hinder the works. When the mineral lies in strata considerably below the surface of the earth, then a perpendicular pit or shaft is sunk to the required depth, and, from its bottom or sides, horizontal galleries are carried to the beds, veins, or strata. The mode of supporting the overlying mass of earth or rock, after the excavation, depends upon the nature of the mineral. Where it is valuable, the roof or cavern overhead, left by the removal of the ore, is propped up by timber or pieces of masonry; but in mines of coal or salt, the whole bed is not dug out, but masses of it are left, like columns, to support the roof.

Of course the ventilation of mines is an important consideration. The mode usually adopted is to cause a current of fresh air from the surface of the earth to descend one shaft, or one-half of a shaft, to supply the place of the impure or noxious air which is made to rise through another shaft, or through the other half of the same. The current is created,

the

in many cases, by large fires at the bottom of the shaft, impure air of which being thereby heated, ascends, and fresh air must descend to take its place. The ventilation of mines depends upon principles well understood. The use of a second shaft is not confined to its necessity for full ventilation, but may also be of the last importance as affording to miners a second place of exit in the event of one being closed by an accident.

The treatment of the ores for the extraction of the metal resolves itself into two distinct operations; one mechanical, the other chemical. The mechanical process adopted depends upon the marketable value of the ore, as the greater its worth, the more labor can be profitably expended on its working. The chemical management depends on the nature of the ore, which must determine whether the extraneous matters Sulphur, Oxygen, etc., can be removed at once, or whether their removal can only be effected after the addition of more oxygen. If the ore be a sulphide, as is the case with Lead, the first process resorted to is that of "roasting" in a reverberatory furnace. When the doors of the furnace are wide open, oxidation more or less complete takes place; while with closed doors the ore is deoxidized or reduced.

The process of roasting consists, then, in oxidation. The Sulphur of the compound unites with Oxygen and volatilizes as Sulphurous acid, whilst the metal also oxidizes and remains in the form of an oxide. Reduction implies, on the contrary, the bringing back of the metal, from the state of combination, to an elementary condition. Carbon and Hydrogen are the great reducing agents. When Hydrogen is passed over an oxide heated to redness, it reduces the oxide, with formation of water, and separation of the metal. The reducing power of Carbon also depends upon the facility with which it unites with Oxygen; but the form in which it will pass off, whether a Carbonic oxide or Carbonic acid, is determined by the nature of the ore. If the metallic oxide is readily reduced, Carbonic acid will be given off, because the temperature required for its reduction is low; but if the temperature at which reduction takes place is very high, the Carbon will pass off as Carbonic oxide. The process of separating a metal from its ore, is called smelting. In carrying out this process, it often becomes necessary to get rid of the Silicic acid contained in many ores, by means of flux. This, as the word itself indicates, is something that will liquefy. The flux employed in smelting an ordinary iron ore consists of Lime, or Calcium oxide, which, uniting with the silicic acid of the ore, forms a liquid "slag" of Calcium silicate. If the lime were not added, the iron oxide would be lost as iron silicate; as soon, however, as the silicic acid is combined with the Calcium oxide, the Carbon and Hydrogen of the fuel act as reducing agents upon the iron oxide. Iron is prepared from its native oxide, or from an artificial oxide made by roasting native carbonate.

To render this matter more intelligible, let us further illustrate it by the example of an iron ore, Ferrous carbonate. Now, a red-heat suffices to rid the ore of its carbonic acid, and the oxygen of the air to turn ferrous into ferric oxide. Fuel would do the rest, and would remove the oxygen from the ferric oxide. But Ferrous carbonate is scarcely ever pure. The so-called Clay-ironstone is Ferrous carbonate mixed with clay (aluminum silicate), lime-stone (calcium carbonate), and other matters. After the ore has been roasted it is ready for smelting, and this is done in the blast furnace. It consists of a truncated, pyramidal mass of brickwork, about fifty feet high, and from fourteen to seventeen feet in diameter in the widest part of the cavity, and with a doubleconed, hollow centre. The lowest portion, or neck of the funnel, is called the crucible, and is made of the most refractory stone. On the sides are the openings for the blast

pipes, through which hot air under pressure is introduced, these being the only openings for the supply of air. Into this furnace a mixture of equal weights of roasted ore and coal, with one-fifth of limestone, are thrown from above. The ore is reduced through the agency of the carbon and hydrogen of the coal, and the silicic acid contained in the clay-ironstone unites with the lime and alumina to form fusible silicates or "slags," which, being lighter than the metal, swim upon its surface. In quantity this slag is five times that of the iron, and is constantly run off from an opening left for the purpose. In the course of a day and night the iron is reduced to a metallic state, and is drawn off into channels of sand. In this state it is known as "pig iron." The gases which escape from the top of the furnace consist principally of nitrogen (from the air), carbonic oxide, hydrogen, and carbonic acid.

CARBONATES AND SILICATES.-As the extent of this article is too limited to allow of any treatment of the metals, some attention may be given to a few metallic salts.

Potassium carbonate is the pearl-ash of the shops. It is a white, granular salt, so very soluble in water that it attracts moisture from the air, and flows into a liquid (deliquesces). Red litmus paper is turned blue by its solution in water. On burning wood, an ash remains consisting principally of this salt; when dissolved in water, and evaporated in iron pots, it constitutes "potash." The metal Potassium or Kalium is made by heating the carbonate with charcoal. Sodium carbonate is well-known as washing-soda. The so-called bi-carbonate of soda is a white powder resembling pounded sugar; it is not nearly so alkaline as the carbonate, because it contains less soda. It is sometimes used to neutralize acidity, to soften water, and for making effervescing drinks.

Calcium carbonate is one of the most abundant of rocks and minerals. In a pure form it is met with crystallized, as "Iceland Spar" and "Calespar." Limestone, chalk, and marble are varieties of Calcium carbonate, and so also is "Coral." Shells also consist nearly entirely of calcium carbonate. In water it is nearly insoluble, as a gallon will only take up two grains. When, however, water contains carbonic acid, as nearly all waters do, then it is much more soluble and gives rise to calcareous waters. This solution of Calcium carbonate gives to spring and sea-waters one of their great characteristics-hardness. Carbonic acid thus breaks down some of the hardest limestone rocks by a purely chemical process, and becomes the occasion of one of the commonest natural phenomena of limestone districts, viz., the enormous natural caverns peculiar to them. The roofs of these are often found clothed with pendent masses of cal cium carbonate which hang like icicles, called by the name of "Stalactites," while their floor is covered with a thick layer of the same nature, formed by the droppings from the stalactites, and known as "Stalagmites." Their formation is due to the facility with which the lime-laden water, when exposed to the air, parts with the excess of carbonic acid; then, as it is no longer able to hold in solution all the calcium carbonate, a portion is deposited.

When a water contains calcium carbonate in solution, it can be softened by boiling; such water is called temporarily hard. The crust of calcium carbonate is a very bad conductor of heat, and very much impedes the boiling of water in kettles and boilers. There are many other carbonates. As a rule, when they are heated to redness, they give off Carbonic acid, and the oxide remains. We have a good illustration of this in the making of "quick-lime" (Calcium oxide): Calcium carbonate becomes Calcium oxide when thus heated.

The silicates are of great importance. Granite is a mixture of various silicates with silicic acid. Both “Mica” and "Felspar" are silicates.

Calcium silicate is contained in window-glass, and is formed by melting calcium carbonate together with silicie acid. "Clay" is silicate, and, indeed, an aluminum silicate. When pure, it is perfectly white, and is used in making china. Heated to redness, clay shrinks, but does not melt, and hence it is employed in making fire-bricks. The common clays are more or less colored, owing to the presence of iron as iron-oxide; they are perfectly insoluble in water, and very retentive of moisture, insomuch that a stiff clay is never deprived of all its moisture by the hottest sunshine.

Glass is a mixture of various silicates, the most important of which are the silicates of potassium, sodium, calcium, and lead. In its most familiar form, glass is a transparent, brittle substance, very ductile just before the point of fusion, and therefore very easily wrought into any desired form. The extent of its fusibility depends altogether upon the nature of the silicates employed. In the manufacture of the superior qualities of glass, everything depends upon the judicious selection of materials. Potassium carbonate must always be employed when perfectly colorless glass is wanted. Soda, although it furnishes a glass of greater lustre than Potash, communicates to it a greenish tinge. Calcium Oxide may be employed as quick-lime, or in the form of calcium carbonate. It is chiefly used in the manufacture of flint-glass. Next to these, lead-oxide ranks in importance as an ingredient in glass-making, its presence being the distinguishing characteristic of flint-glass. It is used both in the form of lead-oxide, and red-lead, a higher oxide of lead. The great use of lead-oxide lies in its power of forming very fusible silicates, possessing a high metallic lustre; but, unfortunately, lead silicate is very soft and easily scratched. Among the essentials to glass-making must be mentioned broken glass and decolorizing agents.

The mixture of the materials for glass-making is effected in large conical crucibles, made of the most infusible fireclay, and which have been previously heated nearly to whiteness. The chemical action is simple, and one explanation will suffice for all kinds of material. If we suppose, for example, the silicic acid to be mixed with potassium carbonate, carbonic acid is expelled, and potassium silicate produced. As long as the solution of carbonic acid lasts, the whole mass is kept in agitation by the escape of the gas, and thus the mixture of the materials is promoted.

The glass, however, does not for a long time become transparent, owing partly to the unwillingness of the last gasbubbles to make their escape, and partly to the excess of lime, and of other earthly impurities that will not fuse. For the purpose of allowing these to settle, and the gas to escape more freely, the temperature of the furnace is raised so as to render the glass as fluid as possible, the process occupying, in all about forty-eight hours. This being accomplished, the temperature is gradually lowered by regulating the draught, so as to allow the glass to assume the pasty consistence, in which it may be readily shaped at pleasure into the required form.

Plate-glass and common window-glass consist chiefly of sodium and calcium silicates, and are therefore made from the raw materials, sand, soda-ash, calcium carbonate, and broken glass. Great care is required that the calcium car bonate be not in excess, as the glass would in that case ap pear milky on cooling.

In many manufactories glass is first blown into the form of a spheroid, which, when its ends are cut off, leaves cylinder which is divided by means of shears, or by a straight line traced by a drop of water. It is then taken to the furnace to be spread out, or flattened by means of a iron rule into a sheet.

Sheet-glass is far less brilliant and more wavy than crownglass, and it is much improved by grinding and polishing. The process of annealing is of great importance, all glass

being inclined to brittleness, and liable to fly. The perfection of the process depends entirely on the temperature of the furnace in which the operation is conducted; if too high, the glass would partially melt and lose its shape; if too low, the plates would be badly annealed, and would be likely to fly when taken out.

Bottles are made of the cheapest materials. The sand always contains ferric oxide (iron-oxide), which not only gives color, but greater fusibility. A heated pipe having been dipped into the melted glass, and a certain quantity thus collected, is withdrawn by a continuous rotary motion; when the glass has become sufficiently consistent not to bend on itself, the blower blows through the pipe, and gives the glass somewhat of the form of an egg. After having introduced it into a mould of a proper form, as soon as the bottle is formed, the blower withdraws it from the mould, and by a see-saw motion raises it on high and in dents the bottom of the bottle. Then, taking a drop of water, he applies it to the neck of the bottle, which is immediately carried to a small cavity in the side of the furnace, and separated from the pipe by a dextrous jerk. The bottle being thus prepared, the blower turns it, and fashioning the pipe to its base, extracts from the pot, with another pipe, a small quantity of melted glass, which he can draw out like thread. The end of this he brings to the neck of the bottle, and, by a rotary motion, surrounds the mouth with a small glass cord; he then introduces the neck into the working hole, and finishes the mouth with pincers. The bottle being completed, an assistant takes it from the hand of the master workman, carries it to the annealing furnace and detaches the pipe by a dextrous blow.

Etching, or engraving on glass, is effected by hydrogen fluoride.

The art of staining must have been nearly of the same age as the discovery of glass; or rather it may be asserted, that it was at all times easier to obtain a colored than a colorless glass. The imitation of precious stones, so commonly found with Egyptian mummies, shows that the knowledge of the various colors obtainable in glass must have been even then very complete. The so-called painted glass, used in our ancient churches, is only superficially colored; the method of coloring the glass throughout now generally adopted, was acquired in the fifteenth century.

Aluminum silicate or clay, is, in its way, as useful as the various silicates which compose glass. Aluminum oxide is better known as alumina, It is found nearly pure as Corundum; "emery" is an impure corundum. The ruby and the sapphire also consist of alumina, tinged with coloring matters.

The metal Aluminum was discovered by Woehler, and derives its name from alum, which is a salt of aluminum and potassium. It is never found native. The chief uses of aluminum are: for the purposes of ornament, the manufacture of small weights, and the production of aluminumbronze-an alloy of copper and aluminum.

The plastic qualities of clay (aluminum silicate), and its power of hardening under the influence of heat, must have suggested at a very early period in the history of man its application in the making of utensils for the many requirements of daily life; while scarcely any art has made greater advances from its rude commencement, and probably none ́has been more indebted for its progress to the aid of science.

The bricks of which our houses are built, the slates and tiles with which they are roofed, the china and earthenware which we use, are all of them but varieties of clays, so abundantly distributed over the earth.

When slowly dried, clay shrinks considerably, and soon exhibits its unfitness, by itself, to form good utensils. It does not fuse even under exposure to the greatest heat of an air-furnace, but shrinks and splits into hard pieces. When

burnt it is still perfectly white, and adheres tenaciously to the tongue. It is greatly absorbent of water, acting like capillary tubes and allowing the water to flow through.

The only clay suitable for the manufacture of porcelain, is that called kaolin or china-clay. But even this is not able to perform all the service required of it, without the assistance of some substitute to obviate the two defects just mentioned as common to all clays, viz., its porosity, and its troublesome property of shrinking as it dries. These faults are entirely remedied by admixture of the clay with silicic acid, the same substance which was found to be so essential in the manufacture of glass.

OTHER METALLIC SALTS.-The carbonates and silicates already mentioned will serve as illustrations of their character: they are very numerous, and their importance can be estimated by the youngest reader.

Sod

The Chlorides are all soluble in water, except "calomel," or mercurious chloride, and silver chloride. Potassium chloride crystallizes in cubes. It is largely contained in kelp, and is consequently a constituent of sea water. ium chloride [NaCl] is our "common salt." Water dissolves rather more than one third of its weight, and deposits a portion, from a hot solution, in cubes. The sea-water about our coasts contains 2-7 per cent., which is equal to rather more than four ounces per gallon. The crystals decrepitate, or break up with noise, when strongly heated, owing to the moisture shut up in them. Our chief source of salt is from salt wells and springs; but there is a deposit of rock-salt in Poland, at Wielitzka, which is no less than five hundred miles long, twenty miles wide, and one thousand two hundred feet thick. Sodium chloride is of much use in the arts. Calcium chloride is a white, deliquescent substance, much used in drying gases. It is always produced in making Carbonic acid from Calcium carnonate. Calcium chloride must not be mistaken for Chloride of lime, which emits Chlorine on exposure to air, and is highly valued as a bleaching and disinfecting agent. It is prepared on a large scale by exposing Calcium hydrate to the action of Chlorine gas: the latter simply drives out water from the hydrate, and takes its place.

Several of the chlorides are employed in making the respective metals. If Magnesium chloride, or Aluminum chloride, be heated strongly with the metal Sodium, Sodium chloride is formed, and the metals Magnesium or Aluminum are obtained.

The Bromides and Iodides resemble the chlorides: some of them are of great importance in medicine as well as in the arts. Potassium bromide is used in the preparation of the element Bromine. Sodium iodide is contained in the ash of sea-weeds, and is resorted to in the manufacture of Iodine. The salt of iodine most valued in medicine, is, however, Potassium iodide.

There is but one Fluoride of importance found native. Calcium fluoride is known as the mineral "fluor-spar," so much used in etching glass. It will be remembered that when Calcium fluoride is treated with sulphuric acid, Hydrogen fluoride passes over.

Hydrogen sulphate. sulphuric acid, has been already mentioned; it is the most energetic of all the salts of Hydrogen, aud is therefore used for setting free other hydrogen salts. Potassium sulphate results from the manufacture of Hydrogen nitrate, and Sodium sulphate from the preparation of Hydrogen chloride. Only a few others can be described. Calcium sulphate is found native as "Selenite," "Gypsum," and "Alabaster." It occurs also crystallized, and requires four hundred parts of water for solution. This salt is contained in many waters, and confers the property of "permanent hardness," as distinctive from the "temporary hardness" of calcareous waters containing calcium carbonate; such a water, on evaporation, deposits a crust difficult