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ness of champaign into whatever it enters, and an acidulated flavour to water. Any acid contained in ans water, may be detected by its turning the infusion of violets, red. Alkalies in water may, in like manner, be detected, by turning the infusion of violets, green. The infusion of dry violets, or paper stained with them, answers best. The infusion of turmeric, or paper stained with turmeric, is rendered brown by alkalies; or reddish brown, if the quantity is minute. When the change is temporary, it is volatile alkali. Sulphur and bitumen may be detected, by the smell and taste. Iron, in mineral water, may be detected by Prussiat of potass, which will precipitate it, and tinge it blue. T'he solution of galls also is an exquisite test of the presence of iron. When there is copper in water, it will show itself on the surface of any piece of bright iron put into it. If arsenic, the residuum will tinge copper, white.

536 The vegetable kingdom affords manifold beautiful instances of the chemistry of nature. Water may be esteemed the chief pabulum of vegetables, which reducing it to its first principles, appropriate its hydrogen and oxygen in the formation of their respective constituent parts.

Air, light, and heat, aid the several processes, whilst the application of manure not only adds to the quantity of nutriment, but at the same time stimulates the vegetating principle to increased action. (See No. 452 to 457.)

537. Vegetable substances, subjected to FERMENTATION, produce, under different circumstances, either WINE, from which ALCOHOL may be obtained, or the ACETIC Acid, termed vinegar. Besides which, the following acids may be obtained from vegetables: benzoic, citric, gallic, malic, oxalic, phosphoric, prussic, tartaric, &c.

538. BITUMENS are certain bodies, which have considerable resemblance to resins and oils, and are found in subterraneous situations.

Obs.--Naphtha is a yellow and transparent fluid, volatile, strongly smelling, and very light; and Petroleum resembles naphtha.

Jet is also a bituminous substance, holding much carbon. Canal coal is of the same class, but contains more earth.

Common coal has its bituminous constituent intersected by plates of carbonate of lime and sulphuret of iron.

539. Animal substances, although containing some of the same principles found in the vegetable kingdom, still manifest considerable differences in their respective analyses.

Gelatine; or jelly, employed in the arts as glue, is abundantly obtained from the skins of animals.

Albumen, is that substance which forms what is termed the white of eggs.

Mucus has been determined by the same chemist to be instanced in the thickening substance contained in saliva, and yields a precipitate on the addition of bitrate of silver, and more fully by acetate of lead.

Fibrin, or the fibrous part of the blood, is obtained froin the muscles of animals, or by agitation and washing of clotted blood.

Urea is a yellow crystalline substance, of a peculiar smell and taste, obtained from urine.

Saccharine Matter is formed in animal processes.

Bones are formed of cartilage, gelatine, and fat, deriving their hardness from the earthy salts which exist in them abundantly. These are phosphate and carbonate of lime, and perhaps a small proportion of magnesia.

Shells are formed of the salts of lime, deposited on animal matter disposed in lamellæ. In bones, the phosphate of lime is most abundant; but in shells, the carbonate of lime prevails.

The Muscles, or flesh of animals, contain albumen, gelatine, and extractive matter, but are chiefly composed of fibrin.

The Skin is divisible into the cuticle, epidermis or scarf-skin, and the cutis 'or true skin. The former appears to consist chiefly of coagulated albumen, and the latter of gelatine: hence, it may be observed, that it is this part from which the jelly is obtained.

Spermaceti is found in the head of the spermaceti

whale; whilst from the blubber is obtained train oil. The fat of some animals, as of the ox and sheep, becomes a hard substance, whilst that of hogs is much softer.

Marrow, which is contained in the long bones of animals, is an animal fixed oil, of peculiar properties, somewhat resembling butter.

Hair, exists in the different forms of down, wool, and bristles.

Feathers appear much to resemble hair in their component parts. The quill, Mr. Hatchett has shown, is chiefly formed of hardened albumen.

Blood separates, on standing, into cruor or coagulum, and the serum or fluid part. The cruor contains fibrin, which is manifested in a white, solid, and elastic form, by washing the clot: and the colouring matter of the blood, which was long supposed to be iron, but is of an animal nature. The serum is a fluid of a greenish yellow, which coagulates at 156°, and is divisible into albumen and serosity. The blood cồntains water, fibrin, albumen, benzoic acid, hydrosulphuret of ammonia, soda, sub-phosphate of iron, muriate of soda, phosphate of soda and of lime.

Bile, secreted by the liver of animals into the gallbladder, is of a dark yellowish green colour, of an unctuous feel, a peculiar smell, and a bitter taste. It contains a resin, and a substance peculiar to bile, named pieromel, a whitish solid substance formed into globules, with water and salts, chiefly phosphate of lime, muriate, sulphate, and phosphate of soda.

Definition 1.-When one chemical substance decomposes another, it is called a chemical test.

2. If salt be mixed in water, it is said to be in solution, and the water is called the menstruum.

3. If no more salt will dissolve, the water is said to be saturated.

4. If we would extract the salt, we must evaporate the water by heat, with a still, or retort, or alembic ;

and if the vapour from either of these pass through a spiral tube or worm, to the receiver, we shall have distilled water; and the residuum of salt will remain in the still

5. Solid substances are reduced into powders by trituration, pulverization, and levigation ; brittle substances are pulverized by means of hammers, pestles and mortars, stones and mullers.

6. The separation of the finer parts of bodies from the coarser is performed by means of sifting or washing.

7. Filtration is a finer species of sifting, performed through the pores of paper, flannel, fine linen, sand, &c. It is used only for separating fluids from solids.

8. Fusion, or the melting of a solid body, by the action of heat, requires, according to their several natures, crucibles of different kinds strong enough to resist the fire ; made of earthenware, porcelain, or a mixture of clay and powder of black-lead, or of blacklead altogether.

9. Sometimes crucibles have covers made of earthenware, but in other cases the fused metal must be exposed to a current of air; for this purpose the crucibles are broad and shallow, and are called cupels.

10. Blow-pipes are used for directing the flame of a candle or lamp against any piece of ore or other substance required to be examined ; and when the inflammable gases are used instead of common air,

the heat is most powerful.

11. The various degrees of heat which are required for the performance of chemical operations, render it necessary that the chemist should also be possessed of a furnace.-See Grammar of Philosophy.

17*

XXII. Electricity and Galvanism.

540. If a piece of glass, or sealing-wax, be rubbed on a piece of dry woollen cloth, or silk, and instantly held over any light substances, they will be attracted towards it, raised on an end, and otherwise put in motion.

The power thus excited is called electric: and if the experiment be made in the dark, the glass and the wax will exhibit faint signs of light ; which light is called the electric fire or fluid.

541. If the glass be of larger dimensions, and turned rapidly round by a winch and a wheel, instead of being rubbed backward and forward with the hand, and be provided with a piece of silk to rub against it during its rotation, streams and large sparks of fluid fire will be elicited, which will fly round the glass, attract light bodies, and produce a pungent sensation.

Obs. 1.-By attracting light bodies, it is meant, that light bodies move towards the electrified body; but it is to be presumed that that which is called attrac tion, is in truth some impulse from without or beyond the light body. The mechanical action of attraction supposed to exist between distant bodies, seems to be an absurdity, and ought to be expunged from science The term repulsion is even more absurd than attrac tion.

Sir Richard Phillips in his Essays, page 92, proposes to substitute for the active verbs attract and repel, the passive ones accide and discede; and their nouns accision and discession, as implying the mere facts of going together and separating.

542. This glass, its cushion of silk, wheel, &c. are called an electrical machine. The fluid, or power produced by it, is one of the most wonderful in nature.

It is found, that it will pass along some bodies, and not along others; that it may be received and diffused

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