tains a resin, and a substance peculiar to bile, named pleromet, 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 sult be mixed in water, it is said to be in'völution, and the water is called the menstruum.

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

4.-If we would extract the salt, we must evaporate the water by heat, with a still, or retort, or alembies and if the vapour from either of these pass through aspiral 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 fri turation, pulverization, and levigation; brittle'substances are pulverized by means of hammers, pestles and mørtars, stones and mullers,

6.-The separation of the finer parts of bodies from the coarser is performed by means of fling or washing. 7.-Filtration is a finer species of sitting, 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, eris cibles of different kinds strong enough to resist the Bre made of earthenware, porcelain, or a mixture of clay and powder of black-lead, or of black-lead altogether,

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

10.-Blow-pipes are used for directing the flame W candle or lamp against any piece of ore or other substancs required to be examined; and when the inflam diable gases are used instead of common air, the heat is 'moit powerful.

11. The various degrees of heat which are requirės for the performance of chemical operations, tender it nes cessary that the chemist should also be possessed of a farHace,See Grammar of Philosophy.

XXII. Electricity and Galvanism.

534. 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.

535. 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 glsss, 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 attraction, 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 attraction.

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

536. 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 on dies, and not along others; that it may be received and diffused by sharp points; that a superabundance of it, in one place, acts as a repellant in the parts immediately adjoining; and that it has a constant and violent tendency to restore its own equilibrium in all bodies

THE ELECTRICAL MACHINE.
Prime Conductor.

Glass Cylinder

537. The bodies, over which it passes freely, are all animals, most animal and vegetable substances, water, &c.; all which are called con ductors of electricity.

But it will not pass over glass, sulphur, charcoal, silk, baked woods, or dry woollen substances; nor through air, except by force, in sparks, to short distances.

All these bodies, therefore, are called nonconductors.

638. The power of exciting it, receiving it on points, and confining it to bodies, over which

it freely passes, by placing these on bodies, over which it will not pass, gives rise to all the paenomena of practical electricity.

Hence a metallic conductor, provided with brass-points, and elevated on glass-legs, is placed opposite the revolving glass-cylinder, to receive by its points the electric power, which is condensed on the cylinder, but unable to escape on account of its being surrounded only by air, and supported by glass legs, both which are non-conductors.

539. If the hand, or a metallic knob, be held within three or four inches from this metallic or main conductor, a large spark will escape, which, in the dark, will be forked, and of the colour of lightning.

There will also be a snapping noise; which, increased by large quantities, would be likely to produce the noise of thunder.

In fact, lightning and thunder are effects of electricity in the clouds.

A flash of lightning is simply a stream of the electric power passing from the clouds to the earth; from the earth to the clouds; or from one cloud to another cloud; and thunder is the report, and the echoes of the report, between the clouds and the earth.

540. But the most wonderful effect of the electric fluid, is its power of suddenly con tracting the muscles of animals when it violently passes through them from one place to another, to restore its equilibrium.

It will not pass through glass; if, therefore,

a plate of glass, in the form of a jar, or otherwise, be coated on both sides, with either gold, silver, or tin-foil, and one side be brought into contact with the main conductor, the other side will instantly part with its electricity, and the plate of glass be said to be charged.

541. If one hand be put to the under or outer side of the said charged plate, and the other hand be brought into contact with the other or charged side, the equilibrium of the two sides will be restored through the body; and a violent contraction, or blow of the muscles will be felt, producing a shock peculiar to this operation.

The severity of the shock, is proportioned to the size of the plate or jar. When many jars are joined together, and charged in this way, they are called a battery; and some bat teries have been made so powerful, as to kill an ox, melt gold, and produce all, the surprising phenomena of real lightning,

542. Philosophers amused themselves, for a century, with experiments on the electrical ap paratus; but a new mode of exciting this power, was discovered by Galvani; and the expe riments made in his way, are called Galvanism.

It is found, that there are two classes of cónductors-perfect, as the metals; and imperfect, as water and the mineral acids; and if these are laid alternately, two perfect and one imperfect, or two imperfect and one perfect, the two ends or sides, will constantly produce an electric shock.