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Obs.In Art. 197 and 128, are described the transformations of insects, from the egg to the worm-the worm to the chrysalis-nd the chrysalis to the butterfly.

The following cut represents those four states in the common caterpillar.

THE EGGS, CATERPILLAR, CHRYSALIS, AND BUTTERFLY.

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306. By Chemistry we ascertain the ingre dients, component parts, or first principles, of which ali kinds of matter are composed.

DEFINITIONS.

-Decomposition implies the separation of the elementary substances of which any compound substance is formed.

2.-Pulverization signifies the mere mechanical separation of podies into smaller ones, without being decomposed into its elementary ingredients.

3.-Chemical affinity affords proof that atoms are compounded in different forms, which coalesce and dovetail together with more or less facility.

4.The sensible atoms appear attracted or repelled accordingly as they, or those of the media in which they are placed, are more or less mutually affected.

5.The substance which decomposes another, is called a chemical test, or re-agent.

6.-If a salt be dissolved in water, it is said to be in solution, and the water is called the menstruum.

7.-When water will dissolve no more of any, substance, the water is said to be saturated.

8.-If we would extract the salt, we must evaporate the water by heat, with a still, a 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 salt will remain in the still.

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

10.-The separation of the finer parts of bodies from the quarser is performed by means of sifting or washing, - 11.-Filtration is a finer species of sifting, performed through the pores of paper, flannel, fiue liucu, sand, &c. It is employed only for separating fluids from solids.

12.-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 black-lead altogether.

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

14,--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 oxygen or hydrogen gas is used instead of common air, the heat is most powerful.

15The various degrees of heat, or atomic motion, which are required for the performance of chemical operations, render it necessary that the chemist should also be possessed of a furnace,

16.Chemical combinations are more generally influenced by the agency of powers, called by the names of attraction and repulsion, but in truth consisting of various susceptibilities of motion in the atoms of bodies, and in the columns of the media in which they are placed.

17. When a new substance is produced from the combination of two others, the operation is called Synthesis. When that substance is decomposed, or resolved into its constituents by the assistance of other chemical agents, the operation is termed Analysis,

18,--Elementary bodies are those which no art of modern chemistry has been able to decompose into other elenients.

19.–Atomic motion produced by percussion, by friction, or by transfer, is the cause of all the varieties of heat, fire, and calorie,

20. Temperature signifies the varied intensity or vio、 lence of intestine atomic motion, which, by increasing the distance of the particles or atoms increases the volunre of bodies.

21.--Different bodies change their states at very dif..... ferent temperatures or degrees of atomic motion. Thus mercury, which becomes solid at about 40o below 0o in Fahrenheit, boils at about 660°; sulphur, which becomes Aund at 2180, boils at 579%,; ether boils at 98«,

2.-- Resistance, says Sir Richard Phillips, is a phanomenon of parting with received motion. A body said to be resisted, is merely parting with its motion to the atoms which it encounters in the media within which it moves; and, as it continues to part with its motion to the radiating atoms, its gradually diminished energy of motion is, in vulgar language, said to be destroyed by resistance.

22-Friction, says he, like resistance, is a mere phenomenon of parting with motion, but to a fixed body instead of a fluid; and being a variation of percussion, or of transfer of motion without change of place, it produces similar phenomena of intestine atomic motion or heat, which, when continued or accelerated, produces all the other phenomena of accelerated atomic motion or heat.

23-Crystallization, he says, is a mere effect of parting with atomic motion, in certain connections with, or relations to, the atoms of the surrounding media, in which the crystallized body is placed.

24.-The following principles should be remembered. 1. That all fluids are combinations of heat (or transferred motion) with various substances;

2. That combustion arises from the action of heat, or motion on the parts of the combustible body; and that the process called burning, is nothing more than the oxygen of the atmosphere uniting with certain parts of the body

3. That oxygen seems to be the acidifying principle: and that all acids are combinations of oxygen with other substances;

4. And that all salts are combinations of an acid with other substances, called the base of the salt.

Obs. Sir Humphrey Davy, in the preliminary observations to his Elements of Chemistry, beautifully observes, that "the forms and appearances of the beings and substances of the external world are almost infinitely various, and they are in a state of continued alteration. The whole surface of the earth even undergoes modifications. Acted on by moisture and air, it affords the food of plants; an immense number of vegetable productions arise from apparently the same materials; these become the substance of animals; one species of animal matter is converted into another; the most perfeet and beautiful

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