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seven proportions, forming acids and oxides. It unites | state in which it occurs in nature, is mineralised by also with chlorine, fluorine, carbon, and sulphur.

Nickel. This metal, when pure, has a white colour, like silver; is rather softer than iron is malleable both hot and cold; is attracted by the magnet; and, like iron, can be converted into one. Its specific gravity is 8-380 after fusion. The preparations of this metal contain poisonous qualities. Nickel combines readily with oxygen, forming two oxides. It also unites with chlorine, carbon, sulphur, phosphorus, and arsenic.

Cobalt. This metal has a grey colour with a shade of red, and is not brilliant. Its texture is granular; it is rather soft and brittle; its specific gravity is 87. It is used for giving a blue colour to glass and porcelain ; the tint is beautiful, and hence the metal bears a high price. It unites with oxygen, and forms two oxides; these are the preparations of cobalt used in the arts. It also combines with chlorine, sulphur, selenium, and phosphorus.

EASILY FUSIBLE BASES.

Of the eight metals composing this family, all are malleable except bismuth, which is not very brittle. They melt at a comparatively low heat. A rod of zinc throws down these metals from their acid solutions in the metallic state.

Zinc.-This metal is of a bluish-white colour, and is composed of plates adhering together. It is a hard metal, being acted on by the file with difficulty; and, after fusion, its specific gravity is 6-896. It becomes malleable at 212°, and melts at 773°, or before it is quite red. When heated red-hot with access of air, it takes fire, burns with an exceedingly beautiful greenish or bluish-white flame, and is at the same time converted into the only oxide of zine with which we are acquainted. It is of a snow-white colour, is tasteless, and insoluble in water. With copper, zinc forms that well-known and useful alloy called brass. Zinc combines with, and is set on fire by, chlorine; it enters into union with phosphorus, sulphur, selenium, iodine, and various metals.

Cadmium. This metal, which is commonly associated with the ores of zinc, has a white colour with a shade of bluish-grey, and resembles tin in its appearance. It is very malleable, and has a specific gravity after fusion of 8-6040. It unites with oxygen, chlorine, and some other supporters, but the compounds are unimportant.

sulphur. The common name for sulphuret of lead is galena. It is abundant in all quarters of the globe.

Tin. This metal resembles lead in many of its properties. It possesses a fine white colour, with a slight shade of blue, and has a good deal of brilliancy. Its specific gravity after fusion is 7-285. It is very malleable. Tin leaf, or tinfoil, as it is called, is about the one-thousandth part of an inch thick, and it might be made much thinner, if requisite. It is ductile, but of inferior tenacity. It is very flexible, and produces a remarkable crackling noise when bended. It melts at 442°, but a very violent heat is required before it will evaporate. It slowly tarnishes with the air, and, when intensely heated, oxygen being supplied, it burns with great brilliancy. Tin combines with oxygen in three proportions, forming the protoxide, which is black, the sesquioxide, which is greyish, and the peroxide, which is yellow. It also unites with chlorine, bromine, iodine, sulphur, selenium, phosphorus, and fluorine. It alloys with various metals. It is used in coating vessels, either in a pure state or alloyed. Pewter is composed of lead and tin; the latter rendering the former, a poisonous metal, quite innocuous. English tin is the best of all, and it is affirmed that it was exported from this island 2200 years ago.

Copper. This metal, in point of general utility, ranks next to iron. It possesses a rose-red colour, and a great degree of brilliancy. Its specific gravity, after being rolled out into plates, is 8-953. It has great malleability, and very considerable ductility. A bar of cast copper, one quarter of an inch thick, requires 1192 lbs. to break it, whilst hammered copper requires nearly 1000 lbs. more to break it. It melts at 1996°; and if the heat be increased, it evaporates in fumes, which are visible. When rubbed, it emits a smell. When heated in a hydrogen flame urged by oxygen, it burns brilliantly, emitting a dazzling green light; a piece of copper in a coal fire tinges the blaze green. When exposed to air, it oxidates into a green carbonate of copper, slowly, and when in contact with moisture. With oxygen it combines in three proportions, forming three oxides, two of which occur native; the other is not a permanent compound. Copper combines also with chlorine, iodine, sulphur, phosphorus, arsenic, and tin. Its alloys with the latter metal are very important. From eight to twelve parts of tin, combined with one hundred parts of copper, compose bronze, and the metal of cannons. Four parts of copper and one of tin compose bell-metal. The alloy used for the mirrors of telescopes was employed by the ancients for the composition of their mirrors. It consists of about two parts of copper united to one part of tin.

Lead. This is one of the most abundant of all the metals, and one of the softest and most fusible. Lead has a bluish-white colour, and a good deal of lustre, but it soon tarnishes. Its specific gravity after fusion, which takes place at 606 is 11:351. Lead is very malleable; it is also ductile, but its wire possesses little Bismuth. This metal has a reddish-white colour, tenacity. By exposure to a very strong heat, it is vo- and is composed of broad plates adhering to each other. latilised, and at the heat of burning hydrogen, urged It is one of the most fusible of the metals, and commuby oxygen, it burns with a bluish flame. While ex-nicates its fusibility to other metals. Its specific gravity posed to the atmosphere during fusion, it imbibes is 9.833. Although not very brittle, it is not malleable, oxygen, and is converted into an oxide. There are unless when heated, nor can it be drawn into wire. A three oxides of lead-the protoxide, which is known mixture of tin, lead, and bismuth, is so fusible, that it in commerce and the arts as a yellow paint, under the melts when thrown into boiling water. A toy of this name massicot, or, if it be semi-vitrified, litharge; the kind is well known; it is a spoon, which, when imdeutoxide is also a paint of a brilliant red colour, in- mersed in a very hot liquid, immediately melts. Bisclining to orange; it obtains the name of minium, or muth combines with oxygen, chlorine, bromine, iodine, red lead; and the peroxide, which is of a deep puce sulphur, and selenium. What is called Newton's fusible brown colour. When heated with sulphur, sponta- metal, is a compound of eight parts by weight of bisneous combustion takes place. Lead also combines muth, five of lead, and three of tin. It melts at 212°. with chlorine, bromine, iodine, sulphur, selenium, arsenic, &c. It is rendered hard by antimony, and the alloy, mixed with a little tin, constitutes the material from which printer's types are elaborated. The salts of lead are numerous and very important. White lead or ceruse, the only white used in all oil paintings, is made by subjecting thin plates of lead, rolled up spirally, to the fumes of vinegar. The lead soon becomes corroded, and assumes a white appearance and a brittle consistency. If this substance be dissolved in acetic acid or vinegar, it becomes sugar of lead. Lead is never found native: by far the most common

Mercury or Quicksilver.-This metal has a silverwhite colour, possesses great brilliancy, and remains fluid at the common temperature of the atmosphere. Its specific gravity, at 60°, is 13:56846; at 39° below zero, when it assumes the solid form, it is 15-612. When solid, it may be beaten out with a hammer, or cut with a knife. When heated to 656°, it boils; and when heated in the open air, it oxidises. The oxides and chlorides of mercury afford an admirable proof of the truth of the atomic theory. It combines also with bromine, iodine, sulphur, selenium, and phosphorus. The compounds which mercury forms with the other

There is a form of this metal which possesses extraordinary properties; it is called spongy platinum. It is prepared by dissolving platinum in a mixture of nitric and muriatic acids by heat; muriate of ammonia is added, when a precipitate falls, which must be filtered and dried. If a small quantity of this powder be heated by a candle, it will become incandescent, as if it took fire. It is, when cold, fit for use. If a jet of hydrogen, from a tube of a very slender bore, be directed on it from a little distance, the metal immediately becomes red-hot, and it sets fire to the hydrogen. This may be repeated a great number of times; but the sponge at last loses its power; the smaller the quantity, the sooner its power is lost.

metals are usually termed amalgams. This metal oc- | phur, selenium, and phosphorus. There are numerous curs in South America and in Spain, in great abun-alloys of platinum, but they are not of much importance. dance. But the mine of Idria, in Carniola, an Austrian province, is perhaps the greatest in the world, and has been wrought for more than three centuries. Silver. This metal is of a fine white colour, with a light shade of yellow. When polished, it displays a great deal of brilliancy and beauty. It is very malable, and may be beaten out into leaves so thin as 1-100,000th of an inch. It is softer than copper, and harder than gold; but its tenacity is inferior to the former metal. When melted and cooled slowly, its specific gravity is 10.3946; when hammered and rolled it is a little higher. Its melting-point is 1830°; and if it be kept melted for a long time, it absorbs oxygen; but it possesses the very singular property of parting with the oxygen on solidifying. Gay Lussac, a great French chemist, says that the presence of a little copper deprives it of this property. Silver forms with oxygen only one well-known oxide. It also unites with chlorine, bromine, iodine, sulphur selenium, phospho- | rus, and arsenic. There are numerous alloys of silver, but few of much consequence. One pound of standard siver is coined into sixty-six shillings, the mint price of silver, therefore, is 5s. 6d. per ounce at present. Silver is found in all parts of the world, sometimes alloyed with a variety of other metals and substances, and sometimes in the native state.

NOBLE METALS.

Some might include silver, and even mercury, in this list, but it is more common to say that the family comprehends six "metals, which all require a violent Leat to fuse them. The name noble metals has been given to the family, because it contains gold and platinum, the most esteemed of all the metals; and because the other four metals belonging to it are usually associated with native platinum eir oxides are reducible to the metallic state by the tion of heat alone. Gold. This is the most w ll the metals. It always occurs in nature, e metallic state, although seldom pure. Its beeful yellow colour, and considerable lust, which telains, not being hable to be tarnished by exposure to the air. It is rather softer than silver, and after fusion it has a specific gravity of 19-2. It is the most malleable of metals, and may be beaten out into leaves no thicker than 1-282,000th of an inch, and the gold leaf with winch silver wire is covered is only 1-12th of that thickness. Its tenacity is considerable, but inferior to that of silver. It melts at 2016". It is insoluble in sulphuric, nitric, and muriatic acid; but it readily dissolves in aqua regia, which is a compound of the two latter. It is difficult to oxidise gold, and still more to barn it; but both can be accomplished. Oxygen combines with gold in two proportions, possibly in three, forming oxides. Gold also unites with chlorine, bromine, dine, sulphur, phosphorus, and arsenic. There are a number of alloys of gold; the standard gold coin of the realm is an alloy of twelve parts of gold to one of copper or silver, or sometimes both. Gold occurs in almost all parts of the world; but Africa and America supply the cinef European consumption.

Palladium, Rhodium, Fridium, and Osmium.-These four metals occur in the platinum of commerce. They are procurable in very small quantities; they have not been applied to any use of moment; they possess no very remarkable qualities, and therefore do not require to be minutely described. They all unite with oxygen and chlorine, and some of them with the other supporters.

Such is a brief sketch of the fifty-four simple substances, whose numerous combinations give rise to the infinite variety of objects which are found ready formed in the laboratory of nature, or have been discovered in that of the philosopher.

ORGANISED STRUCTURES.

The substances constituting the subjects of this branch of chemistry are those of which vegetables and animals are composed. In vegetables, for example, we have sugar, starch, gums, resin, &c.; and in animal bodies, albumen, muscle, bone, &c.

Vegetables. Notwithstanding the infinite diversity of form which vegetable substances assume, it has been proved that they are all composed of the same ultimate elements, and these are only four in number; namely, oxygen, hydrogen, carbon, and azote. These, again, by uniting amongst themselves, form the compounds which constitute the vegetable structure; and being the more immediate objects of sense, in the investigation of any organisation, these are called their proximate principles. Existing ready formed in woods, roots, &c., we find a considerable number of proximate principles, in the form of acids, alkalies, sweet principles, bitter principles, oils, exudations; some poisonous, others wholesome; some spontaneously separating, others remaining obstinately combined. We shall give a brief outline of these.

Citric Acid. This acid exists in the juice of lemons, and, when crystallised, one hundred grains consist ofwaser 233, and pure acid 76, which is a compound of 421 oxygen, 31.58 carbon, and 2-63 hydrogen. Sorbic acid is the sour principle of apples, sorbus berries, and other fruits. It consists of the same ingredients as the former. Tartaric acid is the sour principle of grapes; when a large quantity of them are left to ferment, the result, it is well known, is wine. On the side of the vessel containing this liquor, crystals of the acid combined with potash are formed, and these, Plannum. This metal is white, like silver; its spe- when purified, are cream of tartar. Twelve parts cific gravity is 21-47, so that it is heavier than gold. Its in the 100 are water; and the remaining 88 conhardness is intermediate between copper and iron. It sist of oxygen 52.97; carbon, 32:39; and hydrogen, is very ductile and malleable, though much less so than 2:64 parts. Oxalic acid. The plant called sorrel is gold. Its tenacity is considerable. It will not melt in valued for its acidulous taste, which is conferred upon the heat of our most powerful furnaces, but it may be it by this acid. It has no hydrogen in its composition, fused by the oxihydrogen blowpipe. Its property of consisting merely of oxygen and carbon. It is an active resisting high temperatures without fusion is a most im- poison, and from resembling Epsom salts in appearance, portant one; and on this account, as well as its pro- many persons have fallen victims to its virulence. The perty of resisting the action of most chemical agents, antidote is powdered chalk. Gallic acid is obtained it has been employed in the formation of vessels which from nut-galls. Its most remarkable property is that it is necessary to subject to an extraordinary degree of of changing the colour of solutions containing iron to heat. Like gold, it resists the action of all the single an intense blue-black colour, as in the case of common acids, but dissolves in aqua regia. It combines with oxy-writing-ink. One hundred grains consist of 56.25 carren in probably four proportions, forming oxides. It bon, 37.5 oxygen, and 6-25 hydrogen. Prussic or Hyunites, also, with chlorine, bromine, iodine, silicon, sul- drocyanic acid, found in various fruits and flowers, is a

most powerful poison. It is formed of hydrogen and cyanogen, a noxious inflammable gas. There are a number of other acids, which, being of little use, are not worth naming. Those just described exist ready formed in fruits, &c.; they are simple educts. But there are others formed by chemical changes produced on certain elements contained in vegetables, which afford the base of the acid; these are acid products: some are produced by the agency of fire, others by the action of nitric acid. Several acids, when distilled at a high temperature, undergo decomposition, and new acids are formed. Their names remain the same, with the word pyro as a prefix. Thus we have pyrocitric acid, &c. There are other acids generated by similar means, having simple names without any prefix.

Vegetable Alkalies. It has been ascertained that alkalies, as well as acids, exist ready formed in plants as one of their constituent parts. Those which evince alkaline properties of a weak character are entitled alkaloids. The alkalies are quinina and cinchonia, which resemble each other, have a bitter taste, and neutralise acids. Morphia, which is obtained from opium, is a white crystalline powder; strychnia, one of the most powerful bitters and poisons, which has of late been much used in medicine; brucia, also a violent poison; digitalia, which is procured from the leaves of foxglove; hyosciamia, atropia, veratria, emetina, &c., which are derived from henbane, deadly nightshade, &c. Of the other proximate vegetable principles, the first deserving of notice is the woody fibre which constitutes the solid basis of all vegetable structures. It is called lignin, from lignum, wood; and consists of 52 carbon, and 48 of oxygen and hydrogen, in the ratio which forms water. With lignin are associated various other bodies, such as resins, which are various and abundant. In the different species of the pine-tree, we discover that peculiar liquid resin called turpentine. From resins are obtained what are called essential oils; because, after the resin has been heated in a distilling apparatus, an odoriferous oil distils over, and leaves the resin hard, dark, and odourless. The essence of the substance is supposed to have passed away in the aëriform state, hence the name. From its speedily evaporating on being exposed to the air, it is also called volatile oil. The seeds of plants yield another oil, which not evaporating, is called fixed oil. To these two oils there are two substances bearing some analogy, wax and camphor. The former, when melted, possesses some of the properties of a fixed oil, and the latter seems to possess the properties of a concrete volatile oil, although it possesses qualities distinct from those of all other bodies. Gum, for instance gum-arabic, has the following properties: namely, transparency, tastelessness, perfect solubility in water, viscidity of the solution, capability of cementing fragments and of affording a varnish, and total insolubility in spirit of wine. There is a class of bodies called gum resins, whose properties are intermediate between those of gum and resin; and somewhat allied to resins, although essentially different in most of its properties, is the substance called caoutchouc, or Indian rubber. It is the exuded juice of a peculiar tree, and is composed of carbon and hydrogen. From wheaten flour a substance is obtained, called gluten, from its glutinous nature. There are two principles in this substance the one is called gliadin, and the other zimomin. A substance called vegetable albumen seems to be the basis of all emulsive grains in place of starch, and greatly resembles it. Starch is a fine white sediment, precipitated from the white and brittle parts of vegetables, particularly the tuberose roots, and the seeds of the gramineous plants. One of the most remarkable properties of starch, or, as it is called, fecula, is that of being convertible into sugar by the action of diluted sulphuric acid. Starch is not only afforded from various grains, but from potatoes; and, as extracted from this vegetable, it is much in demand as an article of food. Arrowroot, which is obtained from the roots of a West dia plant, is the same kind of substance.

Sugar.-Every one, we suppose, should know what sugar is; being in particular a sweetener of the kindly beverages tea and coffee. It is derived from many sources from the sugar-cane, maple-tree, beet-root, and grapes. Nothing is easier than its formation from grapes: grape juice is to be saturated with chalk, clarified with white of eggs, or blood, and evaporated; after a few days it assumes the form of a crystalline mass. Tannin.-From oak bark, or nut galls, a peculiar substance is obtained, called tannin-so named from being the material employed in tanning leather. It is inodorous, colourless, and possesses a rough astringent bitter taste.

THE ANIMAL COMPOUNDS.

The chief substances which enter into the composition of animal matter, are oxygen, hydrogen, azote, carbon, phosphorus, and lime. We also find some other kinds of matter, as certain acids and metals, but in quantity so small as not to affect the truth of the above statement, that the foregoing six ingredients constitute the great bulk of the animal fabric.

Bone consists of phosphate and carbonate of lime, and two other ingredients, cartilage and gelatine. The latter is the coagulating, or rather elastic, principle in all animal jellies. When bones are burned in a close vessel, they form ivory black. Fibrin is obtained from the vessels; when recently obtained, it is elastic; but when perfectly dry, it is somewhat horny and transparent. There is an important substance called osmazome, which communicates to soups and broths their peculiar taste and smell, and the greater the quantity present, the better is the soup. The tendons, ligaments, and membranes, are nearly allied to gelatine in their nature.

Of the fluids of the animal body, blood, one of the most important, is viscid, of a red colour, exhaling a vapour of a peculiar odour. When left at rest a few hours, its appearance is very much altered, having separated into two parts-one quite liquid, of a greenish whey-like colour, and called serum; the other an elastic firm jelly, of a crimson red colour and thick consistence, resernbling a deposit, which is called the crassamentum, or clot.

If the clot of blood be repeatedly washed with cold water, it parts with its red colour to the water, becomes white, and a fibrous matter remains, which, when subjected to analysis, proves to be fibrin. Serum coagulates when heated to about 160°, nearly in the same manner as the white of an egg, but the colour is not pure white. If the serum thus coagulated be cut în slices, a fluid will exude which is called the serosity of blood; it consists chiefly of water, holding a little altered albumen and a little common salt in solution. Serum is composed of water, albumen, soda, and some salts of soda. Clot is composed of fibrin, albumen, red colouring matter, a little iron, and carbonic acid.

During the conversion of arterial into venous blood, nitrogen, hydrogen, and other elements, are spent in the formation of new products, while the proximate principles of the blood remain, with an increased proportion of carbon. In this state it is exposed to the atmospheric air in the lungs, the oxygen of which abstracts its excess of carbon, and forms the carbonic acid expired; and this constitutes the conversion of venous into arterial blood.

Fatty substances, as lard and oils, are formed chiefly of carbon, with a little hydrogen and oxygen, one or both. Albumen is a substance very abundant in animal matter. It occurs nearly pure in the white of eggs. Of this substance in the coagulated state, along with gelatine, are horns, nails, and hoofs composed. The brain, the thinking organ of man, consists of water 80, white fat 4:53, red fat 07, osmazome 1·12, albumen 7, phosphorus 1·5, sulphur and various salts 5-15 parts in the hundred.

Printed and published by W. and R. CHAMBERS, Edinburgh. Sold also by W. S. Orr and Co., London.

CHAMBERS'S

INFORMATION FOR THE
THE PEOPLE.

CONDUCTED BY WILLIAM AND ROBERT CHAMBERS, EDITORS OF CHAMBERS'S
EDINBURGH JOURNAL, EDUCATIONAL COURSE, &c.

NUMBER 56.

NEW AND IMPROVED SERIES.

CHEMISTRY APPLIED TO THE ARTS.

PRICE lad.

CHEMISTRY, or that department of physical science which recognises the nature and composition of bodies, and the changes which they undergo, is now indispensable to the proper carrying on of almost every useful at Agriculture, which may be considered the most portant of all the arts, is radically dependent on chetry; for, without a knowledge of that science, the bandman remains ignorant of the nature of his the action of the atmosphere and sun's light, or properties of those materials which are required to rich his exhausted fields. Baking, brewing, distilling, ad, indeed, all the operations by which food is prepared from the condition in which it is furnished by ature, are all in general a series of chemical processes. So likewise is the manufacture of pottery-ware, porceain, glass, paper, the operations of bleaching, dyeing, calico-printing, the preparation of soap, gunpowder, salt, drugs, paints, perfumery, and various other arries daily required. The applications of chemistry the arts are in reality so numerous, that, to do the jeet justice, we should require to take in nearly the while circle of manufacturing industry. To do so, bwever, is beyond our limited means, even were it sirable; and our object in the present sheet is to give short account of the manner in which chemistry is practically applied in those processes of art which we ave not elsewhere alluded to. The design in view is

to teach any one art, but to incite to a general study chemistry among those classes of the people who are gaged in such branches of manufacture as involve an entary change in substance. We commence with a brief description of the apparatus requisite to carry in practical experiments in the science.

THE CHEMIST'S LABORATORY.

A laboratory is a chemist's workshop. It is the place is watch he performs his experiments, and requires to beary and spacious, to have a command of water, to le provided with suitable tables and shelves, mortars, C, and other apparatus. Correct weighing being nispensable to every chemical experiment, an exact and very delicate balance is an essential requisite. There should be at least two balances; one for weighheavy matters, and another for very minute quanThe last instrument should be sufficiently delito weigh from 600 to 1000 grains, and downwards, esting, distinctly and certainly, differences of an exedingly minute amount. As it is by carefully weighing hstances, both before and after being experimented that the exact constituent parts of bodies are determined, and the most important chemical truths tained, the balance and weights should be careEly examined at intervals, and their accuracy tested. Measures are necessary for ascertaining the bulk of gids or gases, and two integers are sufficient, the pint the cubic inch. Measures should be made of glass, and have a graduated scale marked on both sides. They

are commonly of a cylindrical shape, like a phial bottle, and possess a small spout at the orifice. The graduations on these instruments are sometimes very minute, and indicate exceedingly small quantities of the bodies put into them. The measures should be verified by weighing into them successively portions of mercury and water. A cubic inch of the former, at a temperature of 62°, weighs 3425-35 grains, and the same quantity of the latter, at the same temperature, weighs 252-458 grains. Water answers well enough for estimation down to the cubic inch, but for the tenths and the hundredths of an inch, mercury is both more exact and more expeditious.

FURNACES, BLOWPIPES, RETORTS, &c.-Heat is one of the most powerful and extensively useful agents employed by the chemist for ascertaining the properties of bodies, and the methods of its production become of great moment to him. One of the most convenient forms in which heat can be applied to any chemical operation, is that of placing a spirit-lamp, as in fig. 1, under a glass retort, fixed to a simple kind of stand. The lamp is trimmed with cotton wick, and fed by alcohol, which gives a pure flame, and the heat which it generates is very intense.

Fig. 1.

Operations on a more extended scale are carried on by furnaces. Dr Black's portable furnace, which is much used, consists of a stout iron case, like a round stove in shape. Above is an aperture for an iron pot, to contain sand; and other openings may also be ob served, for introducing tubes and different kinds of apparatus. The pipe carrying away the smoke must be prolonged or connected with a chimney. Furnaces upon a large scale are constructed in various ways of fire-brick, which resists an intense heat without fusion. This degree of heat can be produced either by propelling air upon the combustible matter by means of bellows, in which case the furnace is called a blastfurnace, or by forming long flues and raising a high chimney. The higher the chimney is raised, the more powerful is the draught. Upon the top of a furnace of this open kind, and also upon the flues, close by the fire, vessels containing sand, and hence called sandbaths, are placed. In these, bodies can be raised to a high degree of temperature. Charcoal is the substance most commonly used in furnaces. It produces an intense heat without smoke, but very soon consumes. Coke, or charred coal, produces a strong and lasting heat.

The blowpipe is an indispensable article in the labo

Sugar. Every one, we suppose, should know what sugar is; being in particular a sweetener of the kindly beverages tea and coffee. It is derived from many sources from the sugar-cane, maple-tree, beet-root, and grapes. Nothing is easier than its formation from grapes: grape juice is to be saturated with chalk, clarified with white of eggs, or blood, and evaporated; after a few days it assumes the form of a crystalline mass. Tannin.-From oak bark, or nut galls, a peculiar substance is obtained, called tannin-so named from being the material employed in tanning leather. It is inodorous, colourless, and possesses a rough astringent

most powerful poison. It is formed of hydrogen and
cyanogen, a noxious inflammable gas. There are a
number of other acids, which, being of little use, are
not worth naming. Those just described exist ready
formed in fruits, &c.; they are simple educts. But
there are others formed by chemical changes produced
on certain elements contained in vegetables, which
afford the base of the acid; these are acid products:
some are produced by the agency of fire, others by the
action of nitric acid. Several acids, when distilled at a
high temperature, undergo decomposition, and new
acids are formed. Their names remain the same,
with the word pyro as a prefix. Thus we have py-bitter taste.
rocitric acid, &c. There are other acids generated
by similar means, having simple names without any
prefix.

THE ANIMAL COMPOUNDS.

The chief substances which enter into the composition: of animal matter, are oxygen, hydrogen, azote, carbon, phosphorus, and lime. We also find some other kinds of matter, as certain acids and metals, but in quantity so small as not to affect the truth of the above statement, that the foregoing six ingredients constitute the great bulk of the animal fabric.

Bone consists of phosphate and carbonate of lime, and two other ingredients, cartilage and gelatine. The latter is the coagulating, or rather elastic, principle in all animal jellies. When bones are burned in a close vessel, they form ivory black. Fibrin is obtained from the vessels; when recently obtained, it is elastic; but when perfectly dry, it is somewhat horny and transparent. There is an important substance called osmazome, which communicates to soups and broths their peculiar taste and smell, and the greater the quantity present, the better is the soup. The tendons, ligaments, and membranes, are nearly allied to gelatine in their nature.

Of the fluids of the animal body, blood, one of the most important, is viscid, of a red colour, exhaling a vapour of a peculiar odour. When left at rest a few hours, its appearance is very much altered, having separated into two parts-one quite liquid, of a greenish whey-like colour, and called serum; the other an elastic firm jelly, of a crimson red colour and thick consistence, resembling a deposit, which is called the crassamentum, or clot.

Vegetable Alkalies.-It has been ascertained that alkalies, as well as acids, exist ready formed in plants as one of their constituent parts. Those which evince alkaline properties of a weak character are entitled alkaloids. The alkalies are quinina and cinchonia, which resemble each other, have a bitter taste, and neutralise acids. Morphia, which is obtained from opium, is a white crystalline powder; strychnia, one of the most powerful bitters and poisons, which has of late been much used in medicine; brucia, also a violent poison; digitalia, which is procured from the leaves of foxglove; hyosciamia, atropia, veratria, emetina, &c., which are derived from henbane, deadly nightshade, &c. Of the other proximate vegetable principles, the first deserving of notice is the woody fibre which constitutes the solid basis of all vegetable structures. It is called lignin, from lignum, wood; and consists of 52 carbon, and 48 of oxygen and hydrogen, in the ratio which forms water. With lignin are associated various other bodies, such as resins, which are various and abundant. In the different species of the pine-tree, we discover that peculiar liquid resin called turpentine. From resins are obtained what are called essential oils; because, after the resin has been heated in a distilling apparatus, an odoriferous oil distils over, and leaves the resin hard, dark, and odourless. The essence of the substance is supposed to have passed away in the aëriform state, hence the name. From its speedily evaporating on being exposed to the air, it is also called volatile oil. If the clot of blood be repeatedly washed with cold The seeds of plants yield another oil, which not evapo- water, it parts with its red colour to the water, becomes rating, is called fixed oil. To these two oils there are white, and a fibrous matter remains, which, when subtwo substances bearing some analogy, wax and camphor.jected to analysis, proves to be fibrin. Serum coaguThe former, when melted, possesses some of the properties of a fixed oil, and the latter seems to possess the properties of a concrete volatile oil, although it possesses qualities distinct from those of all other bodies. Gum, for instance gum-arabic, has the following properties: namely, transparency, tastelessness, perfect solubility in water, viscidity of the solution, capability of cementing fragments and of affording a varnish, and total insolubility in spirit of wine. There is a class of bodies called gum resins, whose properties are intermediate between those of gum aud resin; and somewhat allied to resins, although essentially different in most of its properties, is the substance called caoutchouc, or Indian rubber. It is the exuded juice of a peculiar tree, and is composed of carbon and hydrogen. From wheaten flour a substance is obtained, called gluten, from its glutinous nature. There are two principles in this substance the one is called gliadin, and the other zimomin. A substance called vegetable albumen seems to be the basis of all emulsive grains in place of starch, and greatly resembles it. Starch is a fine white sediment, precipitated from the white and brittle parts of vegetables, particularly the tuberose roots, and the seeds of the gramineous plants. One of the most remarkable properties of starch, or, as it is called, fecula, is that of being convertible into sugar by the action of diluted sulphuric acid. Starch is not only afforded from various grains, but from potatoes; and, as extracted from this vegetable, it is much in demand as an article of food. Arrowroot, which is obtained from the roots of a West India plant, is the same kind of substance.

lates when heated to about 160°, nearly in the same manner as the white of an egg, but the colour is not pure white. If the serum thus coagulated be cut in slices, a fluid will exude which is called the serosity of blood; it consists chiefly of water, holding a little altered albumen and a little common salt in solution. Serum is composed of water, albumen, soda, and some salts of soda. Clot is composed of fibrin, albumen, red colouring matter, a little iron, and carbonic acid.

During the conversion of arterial into venous blood, nitrogen, hydrogen, and other elements, are spent in the formation of new products, while the proximate principles of the blood remain, with an increased proportion of carbon. In this state it is exposed to the atmospheric air in the lungs, the oxygen of which abstracts its excess of carbon, and forms the carbonic acid expired; and this constitutes the conversion of venous into arterial blood.

Falty substances, as lard and oils, are formed chiefly of carbon, with a little hydrogen and oxygen, one or both. Albumen is a substance very abundant in animal matter. It occurs nearly pure in the white of eggs. Of this substance in the coagulated state, along with gelatine, are horns, nails, and hoofs composed. The brain, the thinking organ of man, consists of water 80, white fat 4:53, red fat 07, osmazome 1·12, albumen 7, phosphorus 1:5, sulphur and various salts 515 parts in the hundred.

Printed and published by W. and R. CHAMBERS, Edinburgh. Sold also by W. S. Orr and Co., London.

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