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sorbs 780 times its volume of this gas, and in this state it is employed for chemical purposes. When the gas is mixed with chlorine, a sudden combustion and detonation take place. The chlorine unites with the hydrogen of the ammonia, and forms muriatic acid, whilst the azote is disengaged in the state of gas. The muriatic acid formed, combines with a portion of ammonia, and forms sal ammoniac. Ammonia is an alkali, and possesses the properties distinguishing this class of substances in a very decided manner. It of course neutralises acids, and the salts which it forms are numerous, and of considerable importance.

CHLORINE.

This is a gaseous body, of a yellowish-green colour, a strong suffocating smell, and of a pretty strong astringent taste. Reckoning air as unity, its specific gravity is 2.5. If breathed undiluted, it destroys animal life ; however, it not only supports combustion, but possesses the remarkable quality of setting fire to many of the metals, even at the common temperature of the air, when beaten out into thin leaves, and introduced into it. The combinations of metals with chlorine are called Chlorides. Chlorine possesses the property of destroying all vegetable colours, and of rendering vegetable bodies exposed to its action white. This property has occasioned the introduction of chlorine into bleaching; for if unbleached linens be exposed to its action, the matter which gives them their grey colour is destroyed, and the substance assumes a brilliant whiteness. Chlorine, however, must be used cautiously, for if applied in its pure and not sufficiently diluted state, it destroys the fibre of the cloth. Chlorine combines with oxygen in four different proportions: two of them contain so much oxygen as to form acids; these are, chloric acid and perchloric acid; but as the other two do not manifest any acid properties, they are to be considered as oxides, and are called protoxide of chlorine and peroxide of chlorine. Besides uniting with oxygen, chlorine combines with hydrogen, and forms the well-known acid called

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discovered only so lately as the year 1826; it resembles chlorine in many of its habitudes. It is of a brownishred colour, very disagreeable smell, sharp strong taste, powerfully corrosive of organic bodies, and, when taken internally, a violent poison. Its specific gravity is 2.96; it destroys vegetable colours almost as powerfully as chlorine. Like chlorine, it sets fire to certain metals when brought into contact with it; it is not combustible, and it extinguishes combustion; it becomes solid at a little below zero; but if combined with water, so as to form a hydrate, it affords fine red crystals at 32°. An acid is formed by the combination of bromine with oxygen, and is called bromic acid; another with hydrogen is called hydrobromic acid. Chlorine also combines with it, and forms a chloride. There are numerous other combinations of bromine, but the compounds are unimportant.

IODINE.

This substance was first discovered in 1811 by a saltpetre manufacturer of Paris. It is derivable from sea plants, and in some of its properties much resembles chlorine, which is also a marine production. If common sea-weed be powdered dry, and treated with sulphuric acid whilst subjected to heat, a violet-coloured vapour is expelled, which, if collected in a vessel, condenses into scaly dark-grey crystals, with somewhat of a metallic lustre. These are iodine, so called from the violet colour of its vapour; iodine being a Greek word, and signifying "violet-coloured." Its specific gravity is 3.0844. Its smell is disagreeable, its taste acrid and hot, and it possesses poisonous properties. It is a powerful stimulant, and has of late been much employed as a medicine. It destroys vegetable colours, but not so completely as chlorine. It melts when heated to 2244°, and volatilises at 3514. It forms a beautiful blue colour when mingled with water holding starch in solution; it is itself slightly soluble in water, but more so in alcohol and ether. Iodine combines with oxygen in three proportions, forming iodic acid, iodous acid, and oxide of iodine; with chlorine, forming chloriodic acid; with bromine in two proportions, forming bromides; and also with azote and hydrogen. A compound of iodine and azote is exceedingly explosive. But a particular account of these substances does not require to be given in this place.

FLUORINE.

The existence of this substance, strange to say, is conjectural; yet its separate identity is supported by the strongest analogies. It exists, or rather is supposed to exist, in fluor or Dei byshire spar, and is thus provisionally called fluorine. If some of this mineral in powder be distilled with strong sulphuric acid, from a leaden retort (a vessel somewhat of the shape of com

Muriatic Acid.-If chlorine and hydrogen be mixed together in equal volumes, and exposed to common daylight in a glass flask, they will in a little time combine, and even explode in combining, if exposed to sunlight or the light of a candle; two volumes of muriatic gas result. Its specific gravity is 1.2844; in its pure state this gas is transparent, colourless, and elastic; under very strong pressure it condenses into a liquid. Water absorbs this gas with avidity. One cubic inch at 69° absorbs 417,822 cubic inches of the gas; heat is produced, and, when cold, the bulk of the water is increased to 1.3433 cubic inches. This is liquid muriatic acid. With these proportions of constituents, its specific gravity is 1-1958; one hundred grains of it consist of 40-39 of real acid, and 59-61 of water. It is a colour-mon Rupert drops) into a leaden receiver kept cold less liquid, and, when exposed to the air, it smokes, because the gas exhaled condenses the moisture of the atmosphere. It extinguishes both flame and life, and is not inflammable. It is of a pungent, suffocating, and somewhat aromatic smell. It powerfully reddens vegetable blues. The best method of obtaining it is by pouring sulphuric acid upon an equal weight of sea-salt, and collecting the gas which is given off over mercury. An immense number of salts are formed from the combination of muriatic acid with oxides; such as common sea-salt, which is a muriate of soda. These are very extensively used, both in the arts and medicine. Chlorine combines with azote, and forms what is called

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with ice, an intensely active fluid is produced. "It has," says Davy, "the appearance of sulphuric acid, but it is much more volatile. When applied to the skin, it instantly disorganises it, and produces very painful wounds. When it is dropped into water, a hissing noise is produced, with much heat, and an acid fluid is formed." This substance has been called hydrofluoric acid, because it is conjectured to have fluorine as a base, combined with hydrogen, to form an acid, upon the principle which we have formerly described. Other views have been adopted with respect to this substance, but the above is the one now generally admitted.

CARBON.

Carbon or charcoal is found in many different forms, and can be prepared by burning wood, coal, &c., in close vessels. The diamond is pure carbon, and plumbago or black-lead is principally composed of this substance with a little iron. It burns in oxygen with considerable brilliancy, although in common air it emits but a feeble light. If carbon be burned in a close vessel, filled with oxygen, the carbon will be entirely consumed, and the oxygen so much changed, that if a

lighted taper be put into it the light will be extinguished. Carbon combines with all the supporters of combustion, and with oxygen forms carbonic acid. This acid may be prepared in the pneumatic trough, by putting into the retort an ounce of hydrochloric acid, previously mixed with two ounces of water, along with a tablespoonful of the carbonate of lime. An effervescence takes place between the acid and the lime, carbonic acid gas being given off, which can be collected in the jars and condensed in water. Carbonic acid is fatal to animal life, and the gas will extinguish a candle introduced into it.

Oxalic Acid. This substance, which is also a combination of carbon with oxygen, may be formed by digesting sugar along with nitric acid. The acid is deposited in small crystals, which have an intensely acid taste, and, when taken internally even in small quantities, destroys life. It combines with bases, and forms a genus of salts called oxalates. Carbon is capable of uniting with chlorine in three different proportions, with bromine in one or two, and with iodine in two. But we must pass from these compounds to those of far greater moment which it forms with hydrogen.

There are many combinations of carbon with hydrogen, and much uncertainty prevails both with regard to their number and nature; they are all designated by the name hydrocarbons, or more properly hydrocarburets.

COAL GAS.

Carbureted and bicarbureted hydrogen bear very different relations to the well-being of man: the former, when a spontaneous production of nature in mines, is one of the most terrific instruments of destruction, and a great obstacle to human industry; for, by mixing with a certain quantity of common air, it acquires the property of exploding when accidentally kindled, and thousands of human lives have fallen sacrifices to its violence, until Sir Humphry Davy's invention of the safety-lamp divested it of its terrors.

Davy's safety-lamp consists of a common lamp surrounded with wire-gauze. On analysing the carbureted hydrogen or fire-damp, Sir Humphry Davy found that it would not explode when mixed with less than six times, or with more than fourteen times, its volume of atmospheric air; that air rendered impure by the combustion of a candle will not explode fire-damp, though the candle will still burn for a time; and that, if a candle be burnt in a close vessel, with small apertures only above and below the flame, no explosion will ensue. The flame within will be enlarged, but no explosion take place; and it was found that the gas from mines will not explode in a tube less than one-eighth of an inch in diameter.

Bicarbureted hydrogen is the chief, although not the most abundant ingredient in coal gas, now so generally used for illumination; the other ingredients are carbureted hydrogen, hydrogen, and carbonic oxide. Coal gas is made by introducing a quantity of bituminous coal into a large iron cylinder called a retort, close at one end, and furnished with a mouth-piece at the other, for closing or opening it; there is also a tube for carrying off the gas and other products as they form. A quick strong heat is applied round the cylinder, and a vast quantity of gas, composed of the four ingredients just mentioned, is thus extricated, with tar and an ammoniacal liquor, both of which are condensed by passing through pipes immersed in cold water. There is a great difference in the relative proportions of the gases in the mixture, as also in the quantity of tar, according to the quality of the coal and the mode of applying the heat. The more tar the gas holds dissolved, the more dense will be the flame when the gas is made to burn, and the more disagreeable will be the smell when it is not burning. A slow heat gives much tar and little gas, and that little of a poor quality; a quick heat gives much gas, of good quality, and less tar. Owing to these and other causes, the illuminating power of coal gas varies much. Before it is let through the conducting tubes for public consumption, it is well agitated in

contact with a mixture of lime and water, or passed through strata of loosely strewed hydrate of lime: it is thus deprived of much of its smell, and also of some of its illuminating power. On an average, a chaldron of good Newcastle coal, weighing 25 cwt., will afford 12,000 cubic feet of gas, provided that the retorts are new. After being used a few months, the product will not exceed 11,000 feet, or even 10,000. An illuminat ing gas of this kind is sometimes presented ready formed by nature. A village of Fredenia, in the western part of the state of New York, is lighted with this gas as it naturally issues from a rock; the flame is large, but not quite so brilliant as that of coal gas.* A scheme was recently in agitation for lighting the towns of Newcastle and Gateshead with a natural gas which issues from the Wallsend coal-pits. This gas is diluted with about 10 per cent. of atmospheric air, but is otherwise remarkably pure. Oil gas being of a similar nature, it need not be particularly described. There are other less important compounds of carbon and hydrogen, and the whole correspond with the law of multiple combu nation already described. Naphtha and naphthaline are hydrocarburets; the former is a transparent volatile fluid, the other is a transparent volatile solid, which assumes the form of crystalline plates: both are obtained from coal tar by distillation.

Cyanogen. This substance is a gaseous compound of azote and carbon. It burns with a purple flame, and destroys life on being breathed. Cyanogen unites with a variety of bodies, and forms many important compounds.

BORON

The borax of commerce is a compound of boracie acid and the alkali called soda. Boracic acid is a compound of oxygen and boron, in the proportion, it is supposed, of one atom of the latter to three of the former. Pure boron is an opaque brownish-olive powder, infusible, and not volatile at any temperature to which it has as yet been subjected. It neither dissolves in nor acts upon water. At about 600°, it takes fire, and combines with oxygen, forming

Boracic Acid. This substance evinces the usual properties of an acid, but it is not a powerful one at ordinary temperatures. At high temperatures, however, it displaces the strongest of the other acids, and is exceedingly useful in fluxing out the baser metals from the nobler. When the acid is detached from borax, by vitriol being poured upon that compound, it exhiluts itself in scaly crystals. It dissolves in rectified spirit, and, if the solution be set on fire, it burns with a green flame. Borax itself, when heated, melts into a perfectly clear glass, which is the basis of some artificial gema of considerable beauty. Borax communicates its own fusible nature to other bodies, and hence is used as a flux. Flux is a general term made use of to denote any substance or mixture employed to assist the fuse in of minerals. There are a considerable number of such bodies; the alkalies are those most generally used. Boracic acid is the only known compound of boron with oxygen. There has been no compound yet discovered of boron with either bromine or iodine, but it com bines with chlorine, forming a gaseous acid, to which the name of borochloric acid has been given; and als with fluorine, forming

Fluoboric Acid, which exists in the gaseous state. It is colourless, has an exceedingly acid taste, and a sme similar to muriatic acid. It contains no water, but possesses a powerful affinity for that fluid, and is on that account sometimes used as a test of the preselio of moisture in gases. Its specific gravity is 2:362; an it seems to consist of one atom of boron and three of fluorine. The combinations of boron with hydrogen, azote, and carbon, are still unknown.

SILICON.

Quartz, or rock-crystal, which constitutes so com derable a portion of the crust of the earth, cons. 's

* Donovan's Chemistry, p. 117.

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to five atoms of oxygen. Phosphorus also produces another acid called phosphorous acid, containing a smaller proportional quantity of oxygen; and a third, called hypophosphorous, containing still less of the gas. Phosphureted Hydrogen.-This gas is colourless, has a smell like garlic, and a very bitter taste; its specific gravity is 17708. It burns spontaneously. When mixed with oxygen, rarefaction causes them to explode, as condensation produces explosion in other gases-a very remarkable property of this substance. This gas may be detonated, also, with protoxide and deutoxide of azote. When mixed with chlorine gas, it burns with a greenish-yellow flame. It is composed of equal volumes of hydrogen gas and phosphorus vapour. There are other compounds formed of these two substances; and phosphorus combines also with chlorine, bromine, and iodine, in two proportions each. It likewise unites with fluorine, carbon, sulphur, and selenium.

ARSENIC.

The White Arsenic of commerce is a combination of arsenic and oxygen. When mixed with black flux (which is composed of cream of tartar and about half its weight of nitre, heated to redness in a covered crucible), and subjected to heat, it is reduced to the metallic state. It has a bluish-white colour, is soft, brittle, and easily reduced to fine powder. Its specific gravity is 5-672. When moderately heated, it evaporates, com bining with oxygen, and forming the arsenic of commerce, so well known for its destructiveness to animal life. With oxygen, arsenic forms two acids, the arsenous and arsenic. Arsenous acid is a white, brittle, compact substance, having a weak, acrid taste, which at last leaves an impression of sweetness. It is one of the most virulent poisons known. Arsenic acid is quite similar in its constitution to phosphoric acid. Arsenic combines with chlorine, bromine, iodine, fluorine, hydrogen, sulphur, phosphorus, and selenium.

ANTIMONY.

This is a metal which, when pure, possesses a silverwhite colour. Its compounds are well known, being much used as a medicine. Its texture is fibrous, and it is easily reduced to powder by being pounded in a mortar. Its specific gravity is 6'4366. It melts when heated nearly to redness, and at a higher heat it is sublimated in white fumes. It combines with oxygen in three proportions, and forms three compounds, two of which possess acid properties. The other is an oxide, which constitutes the base of all the active medicinal preparations of this metal. With chlorine it combines in two proportions, forming two chlorides, which are analogous to two of the compounds formed with oxygen. It also combines with bromine, iodine, fluorine, sulphur, selenium, phosphorus, and arsenic. Antimony is extensively used in the arts, particularly in typefounding and stereotyping.

TELLURIUM.

This substance is a metal, having a silver-white colour, and considerable brilliancy. It has a laminated texture, is brittle, may easily be reduced to powder, and has a specific gravity of 6-1379. It fuses at a temperature rather higher than that which is necessary to melt lead. It combines with oxygen, and forms oxide of tellurium. This compound possesses at once acid and alkaline properties. When tellurium is heated before the blowpipe, it burns with a blue flame, emitting a white smoke, which is the oxide. Tellurium burns spontaneously in chlorine gas, and forms a chloride of tellurium. It also unites with iodine, hydrogen, and carbon. The other combinations of this metal are still unknown.

CHROMIUM.

This is a metal of a whitish colour and a brittle consistency. Its specific gravity is 59. It requires a very high degree of heat to melt it, and is only obtained

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pure in small grains. No acid readily dissolves it, except the fluoric. Chromium combines with two proportions of oxygen, forming two compounds, which have received the names of green oride and chromic acid. Chromium unites with chlorine, sulphur, phosphorus, and probably fluorine. It is used in coloured glass making, and glass and porcelain painting. It is also used in enamelling, and as a rich, strong, and durable pigment. To glass and enamel it communicates a green colour, but to the painter it affords one of his prettiest yellows.

VANADIUM.

This is a metal which was only discovered a few years ago. It is white, resembling silver, brittle, a good conductor of electricity, and is easily dissolved in nitric acid and aqua regia. When heated rather under redness, it takes fire, burns with a dull flame, and is converted into a black-coloured oxide. It combines with oxygen in three proportions, forming, first, black oxide or protoxide, the binoxide, and venadic acid. It combines also with chlorine, sulphur, and phosphorus, but its other compounds are unknown.

URANIUM, MOLYBDENUM, TUNGSTEN, COLUMBIUM, AND

TITANIUM.

These substances are all metals, but on account of their scarcity, or from the difficulty of reducing them to the metallic state from their ores, they are but imperfectly known, and have not been applied to any useful purpose. Uranium has an iron-grey colour, of considerable lustre, and, when heated to redness, takes fire. It produces a deep green protoxide, which gives a black colour to porcelain, and a fawn-coloured peroxide, which communicates to porcelain an orange colour. Its specific gravity is 9. Molybdenum has a silvery-white colour, is brittle, and has a specific gravity of 8-636. Tungsten is of a greyish-white colour, is very hard and heavy, having a specific gravity of 174. Columbium, when burnished, assumes a yellowish-white colour and a metallic lustre. Titanium has a copperred colour, and considerable brilliancy. It crystallises in cubes, is hard enough to scratch rock-crystal, and has a specific gravity of 5.3. All these metals combine with oxygen and some of the other supporters; but the oxides and acids so formed are not deserving of particular mention.

ALKALINE BASES.

Potassium is the base of that well-known and very useful article potash. The properties of potassium were first determined by Sir H. Davy, to whom we are indebted for the discovery of the composition of the alkaline bodies. It is a white metal, like silver. At 32° it is hard and brittle, at 50° is soft and malleable, at 1324° melts, and at a low red heat evaporates. Its specific gravity at 60° is 0.865, being lighter than water. When exposed to the air, it rapidly absorbs oxygen, and forms potash. This latter body, as found in commerce, is always combined with water, which cannot be expelled by heat. When potassium is thrown on the surface of water, which it swims upon, it decomposes that fluid with such rapidity, that the metal takes fire, and burns with a red flame. Potassium combines with two propor tions of oxygen; it also unites with chlorine, bromine, iodine, hydrogen, sulphur, and several other bodies.

Sodium is a metal so similar in most respects to the foregoing, as to stand in no need of particular description. It is the base of the alkali called soda, which is formed when the metal is brought into contact with water, or when it is heated in oxygen. It decomposes water, and in its relations to other bodies, bears a strong resemblance to potassium.

Lithium.-This metal is the base of the alkali called lithia, which is of a white colour, and has a taste fully as caustic as that of potash itself. It is of course au oxide of lithium. Lithium likewise unites with chlorine, but its other combinations are unknown.

Barium. This metal is the basis of barytes, an alka

when wet, is somewhat plastic, like alumina. It neither dissolves in water nor melts in the fire. Its salts have a sweetish taste, like those of alumina ; and both of these earths are in this respect opposed to magnesia, which with acids affords salts of a bitterish taste. Glucinum combines with chlorine, phosphorus, sulphur, selenium, iodine, and bromine.

line earth. It is of a white silvery appearance, absorb- | 44 44 oxygen, is a soft, tasteless, white powder, which, ing oxygen rapidly by exposure to the air, thus forming barytes; and it also rapidly decomposes water. Barium combines also with sulphur and phosphorus, and forms compounds with chlorine, bromine, and iodine. Strontium. This metal is the base of strontia, an earth very similar to the foregoing. Strontium and barium resemble each other very much in most of their properties, and their combinations with oxygen have also a very strong resemblance. Strontium also unites with chlorine, phosphorus, and sulphur.

Calcium. This metal is the base of the well-known and indispensable commodity lime. Lime has been known from the remotest ages, and appears always in combination with an acid, most commonly with the carbonic, constituting limestone, marble, calcareous spar, chalk, and frequently, with sulphuric acid, constituting gypsum, selenite, and sulphate of lime. It combines also with various other acids. Calcium is white, like silver, solid, and much heavier than water. When heated in the open air, it burns brilliantly, and quicklime is produced. Calcium unites with oxygen in two proportions, forming lime and peroxide of calcium. Pure lime has an acrid taste, and is sparingly soluble in water. It, however, readily absorbs water poured upon it, and swells, producing at the same time a great heat. The fact is, that the water becomes solidified, and of course gives out a great quantity of heat, which accounts for the rise of the temperature. This process is called slaking lime. Lime combines with chlorine, and forms chloride of lime, a substance which has become an important article of commerce under the name of bleaching-powder. It is a white powder, with a hot taste, having the power of destroying vegetable Calcium combines with sulphur and phos

colours. phorus.

Magnesium. This metal is the basis of magnesia, a substance universally known from its frequent employment in medicine. Magnesium is obtained in brown scales, which, when rubbed against agate, leave a metallic stain, of a leaden colour. It burns with a red light, and, by thus combining with oxygen, becomes magnesia. This is a soft, elastic, tasteless powder, not sensibly soluble in water, and slowly changing vegetable blues to green. Magnesium forins salts with chlorine, bromine, and iodine.

EARTHY BASES.

This family comprehends five substances, the oxides of which are white tasteless powders, distinguished by the name of earths.

Yttrium.-Yttria, which constitutes the oxide of this metal, is obtained from a scarce mineral called gadolinite. Yttrium is procured from it in iron-grey scales. If heated in common air or oxygen, it burns brilliantly, forming the earth yttria; and as far as is known, this is the only compound formed by the union of oxygen and yttrium. The latter substance combines with chlorine and the combustibles.

Cerium. This metal exists in a reddish-coloured mineral found in Sweden, called cerite. Cerium is a dark-grey powder, having a metallic lustre, but its properties have not yet been properly determined. It, however, combines with oxygen, chlorine, carbon, sulphur, and phosphorus.

Zirconium.-The earth called zirconia is a harsh whitish powder, destitute of taste or smell. The base zirconium is composed of brilliant scales, which are probably metallic, although the substance has not as yet evinced the metallic lustre. When heated in common air, it takes fire, and is converted into zirconia, which is perfectly white. This is the only compound which it forms with oxygen. It unites with chlorine, carbon, and sulphur.

Thorium-This is a newly discovered metal, of a leaden-grey colour, heavy, and under the burnisher shows metallic lustre. If it be heated in open air, it burns with much splendour, and the resulting snowwhite oxide is the earth called thorina. This is the only compound of thorium with oxygen, and the resulting substance is distinguished from the other earths by various properties. Thorium, when heated in vapour of sulphur, burns, and it also unites with chlorine and phosphorus.

DIFFICULTLY FUSIBLE BASES.

Iron. This well-known substance is one of the seven metals with which the ancients were acquainted; these were gold, silver, copper, iron, tin, lead, and mercury. Iron is a metal of great utility, and it is fortunately found abundantly. Almost every mineral contains it. The ore from which the iron of Great Britain is obtained, is a carbonate of iron. Iron, after passing through a fiery ordeal, has a greyish colour, a metallic lustre, and, Aluminum.-Alumina, which, when pure, is a fine when burnished, a good deal of brilliancy. Its hardlight powder of brilliant whiteness, is an essential con- ness exceeds that of most metals, and, when in the state stituent in every kind of clay, and constitutes the base of steel, it may be rendered harder than most bodies. of alum, from which substance it may easily be obtained. Its specific gravity is 7.843 after hammering. It is It is a compound of oxygen and aluminum, consisting attracted by the magnet, and may itself be converted of two parts of the former to three of the latter. This into a permanent magnet. It is malleable at every metal, when burnished, assumes a metallic lustre re- temperature, very ductile, and very combustible, for sembling that of tin. It is not easily fused, but at a we see a thin wire burn in the flame of a common candle. red heat it burns with great splendour, and is converted It burns brilliantly in oxygen, with which it combines into alumina. This substance, so useful in the manu- in two proportions, forming oxides. It combines also facture of every species of pottery, is the only compound with chlorine, bromine, iodine, boron, sulphur, selenium, known of oxygen with aluminum. Alumina possesses phosphorus, arsenic, chromium, and antimony; but the the remarkable property of shrinking into less bulk most important of its combinations with simple subaccording to the intensity of the heat which is applied to stances are those with charcoal, which form the imit; hence, it was formerly employed as a kind of ther-portant compounds cast-iron and steel. Iron forms with mometer, or rather pyrometer, for measuring very high degrees of temperature, in furnaces for instance. A gauge is used for measuring the amount of the contraction. Aluminum combines with chlorine, phosphorus, sulphur, and selenium.

Glucinum. Glucina, which is the oxide of glucinum, exists to about fourteen per cent. in the beryl or emeraid, from which it can be extracted. Glucinum is a dark-grey powder, which, when burnished, acquires the metallic lustre. It is very difficult of fusion. When heated in air or oxygen, it burns brilliantly, and affords the oxide glucina-the only compound which it forms with oxygen. Glucina, which consists of 100 metal and

the acids a numerous and valuable class of salts.

Manganese. When this substance is pure, which is rarely the case, it is rather whiter than cast-iron, of a granular texture, and may be reduced to powder by pounding. Its specific gravity is 8013. It is attracted by the magnet only at a very low temperature. It gradually absorbs oxygen from the atmosphere, and decomposes water, a property which it loses when alloyed with iron. It is much in use. Glass-makers use it for two purposes; first, for communicating a purple or violet colour, or for destroying all colour, and rendering the glass colourless. Manganese has a strong affinity for oxygen, with which it combines in

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