Слике страница

to the receiver, we shall have distilled water : and the salt will remain in the still,

9. Solid substances are reduced into powders by trituration, pulverisation, and levigation ; brittle substances are pulverized by hammers, pestles and mortars, stones and mullers.

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

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

12. Füsion, 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 black-lead altogether.

13. 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.

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 coramon air, the beat is most powerful.

15. The various degrees of heat, or atomic motion which are required for the performance of chemical operations, ren. der it necessary that the chemist should alo 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 wbich they are placed.

17. When a new substance is produced from the combinations 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 sérmed analysis.

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

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

20. Temperature signifies the varied intensity or violence of intestine atomic motion, which, by increasing the distance of the particles or atoms increases the volume of bodies.

21. Different bodies change their states at very different

temperatures or degrees of atomic motion. Thus mercury, which becomes solid at about 40 degrees below 0 in Faren. heit, boils at about 660 degrees : sulphur, which becomes fluid at 218 degrees, boils at 579 degrees; ether boils at 98 degrees.

22. Resistance, says Sir Richard Phillips, is a phenomenon 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.

23. Friclion, 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.

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

25. 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 df 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 combination of an acid with other substances, called the base of the salt.

Obs.-Sir Humphrey Davy, in the preliminary observations to his Elements to 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 perfect and beautiful of the forms of organized life ultimately decay,

[ocr errors]

and are reso!ved into inorganic aggregates : and the same elementary substances, differently arranged, are contained in the inert soil, or bloom, and emit fragrance in the flower: or become in animal, the active organs of mind and intelligence. In artificial operations, changes of the same order occur: substances having the characters of earth, are converted into metals; clays and sands are united, so as to become porcelain ; earths and alkalies are combined into glass ; acrid and corrosive bodies are formed from tasteless substances; colours are fixed upon stuffs, or changed, or made to disappear; and the productions of the mineral, vegetable, and animal kingdoms, are converted into new forms, and made subservient to the purposes of civilized life. To trace, in detail, these diversified and complicated phonomena, to arrange them, and deduce general laws from their analogies, is the business of Chemistry.”

516. The ancients conceived that there were but four elements, or first principles-Air, Water, Earth, and Fire.

The moderns have analyzed these four elements, and have discovered other elements of those elements, viz. Oxygen, Hydrogen, Nitrogen, Chlorine, Carbon, Caloric, (or atomic motion) Sulphur, Phosphorus, nine Earths, and twenty-eight Metals.

Obs. 1.-Atmospheric Air is now found to be a compound of Nitrogen or Asole ; and Oxygen ; which are preserved in a gaseous state by Caloric.

WATER is found to be a compound of Oxygen and Hydrogen.

EARTI is a compound of nine different substances, now called Earths. (See 526.)

And FIRE is found to consist of mere atomic motion.

2.--The forms of matter are well arranged into three distinct classes, by SIR H. Davy. The first class consists of solids ; which compose the great known part of the globe. Solid bodies, when in small masses, retain whatever mechanical form is given to them: their parts are separated with difficulty, and cannot readily be made to unite after separation; some solid bodies yield to pressure, and do not recover their former figure when the compressing force is removed, and these are called non-elastic solids ; others, that regain this form, are called elastic bodies. Solids differ is degrees of hardness ; in colour ; in degrees of opacily or transparency ; in densily, or in the weight afforded by equal volumes ; and

when their fornis are regular or crystallised, in the nature of these forms.

The second class consists of liquids ; of which there are much fewer varieties. Liquids, when in small masses, assume the spherical form; their parts possess freedom of motion; they differ in degrees of density and tenacity ; in colour and degrees of opacity or transparency. They are usually regarded as incompressible ; at least a very great mechanical force is required, to make them occupy space perceptibly smaller.

The third class, elastic fluids or gases, exist free in the atmosphere ; but they may be confined by solids, or by solids and fluids, and their properties examined. Their parts are easily moveable; they are compressible and expansible ; and their volumes are in versely, as the weights compressing them. All known elastic fluids are transparent, and present only two or three varieties of colour; they differ materially in density.

3-Besides these forms of matter, which are easily submitted to experiment, and the parts of which may be considered as in a state of apparent rest, there are other forms of matter which are known to us only in their states of motion when acting upon our organs of sense, or upon other matter, and which are not susceptible of being confined. They have been sometimes called ethereal substances, .which appears a more unexceptionable namne than imponderable substances. It cannot be doubted that there is matter in motion in the space between the sun, the stars, and our globe; though it is a subject of discussion, whether successions of particles be emitted from these heavenly bodies; or motions communicated by thenu, to particles in their vicinity, and transmitted by successive impulses to other particles. Ethereal matter differs, either in its nature, or in its affections, from motion ; it produces different effects-radiant heat and different kinds of light.

517. CALORIC, say many chemists, is a mere name of that element or principle, which, combined with various bodies, produces the sensation of heat; but, according to the theory of Sir Richard Phillips, there is no such element, and all the phenomena are mere effects of atomic-motions.

Obs. 1. --Body, says be, is susceptible of two varieties of motion : (1) a motion or impulse of an aggregate, which occasions it to change its place in regard to other aggregates;


[ocr errors]

and (2) a motion of the atoms of an aggregate, created when any impulse from any cause cannot produce commensurate change of place in the aggregete and diffuse the motion, so that, by re-action, the impulse terminates within the body in the mutual actions of its component atoms.

2.--Motion of both kinds, says Sir R. Phillips, continues to affect a body, until it has been imparted or transferred to ag. gregates in contact, or has been diffused or radiated through the medium in which it is immersed; and this law of the equalization of motior., by the contact of moving aggregates and atoms with others susceptible of receiving and diffusing the motion, is the proximate cause of all varieties of material phenomena.

3.-Motion appears, therefore, to constitute the life, powerz and energy of matter; and is the active soul of the Universe. Matter is its patient, and the relative phenomena of bodies are the results. As it acts on Aggregates by contact, or by impulse, on and through media, it constitutes the object of Physical Philosophy; and, as it affects compounds or structures of Atoms, it is the object of Chemical Philosophy.

4.-When percussion or collision does not produce an equal quantity of aggregate motion in a proportionate change of place in the aggregate ; or when the motion received cannot be transferred by diffusion, as when a piece of iron, laid on an anvil, receives the motion of a hammer, or when two pieces of wood are rubbed together, an intestine re-action of the atoms in the iron and wood takes place, accompanied by the perception of heat, and by a series of phenomena depending on the quantity of motion thus concentrated, and on the acceleration of the same by reiterated blows, rubbings, or transfers of motion.

5. This intestine motion produces various phenomena of the several component atoms of the affected body in regard to one another, and to the heterogeneous media in which they are situated: thus, one quaplity creates a perception of heat, another sensibly imparts that perception to the atoms of the surrounding media, another converts the fixed mass into fluids, an acceleration converts the fluids into diverging gas, and a further acceleration, which exceeds the radiating powers of the surrounding media, decomposes those media, exhibiting flame and intense heat, in the solidification of the oxygenons part of the media, and producing subtle radiations on the rare medium which fills space, thereby affecting the nerves of the eye, imbued with that medium, with the perceptions of light.

6. The parting with each degree of atomic motion produces

« ПретходнаНастави »