« ПретходнаНастави »
Obs.] Art. 197 and 128, are described the trano. formations of insects, from the egg to the scorm -- tho worm to the chrysalis and the chrysalis to the butterfly.
The following cut represents those four sinter in the common caterpillar. TILL EGGS, CATERPILLAR, CHRYSALIS, AND
XXI. Chemistry. 306. By Chemistry we ascertain the ingredients, component parts, or first principles, of which ali kinds of matter are composeed.
DEFINITIONS 1.- Decomposition implies the separation of the ele. mentary substances of which any compound substance is formed.
2.-Pulverization signifies the mere mechanical separation of bodies 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 dove tail together with more or less facility.
4.-The sensible atoms appear attracted or repelled ac. cordingly 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-ngent.
6.-If a sult be dissolved in water, it is said to be in rolution, 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 hent, 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 trin turation, pulverization, and levigation, brittle substances are pulverized by means of hammers, pestles and more tars, stones and mullers.
10.-.-The separation of the finer parts of bodies from the quarser is performed by means of si/ling or washing:
11.-Filtration is a finer species of sitting, performed through the pores of paper, flannel, fiue liucu, sand, &c. It is employed only for separating fluida from solide.
12... Fusion, or the melting of a solid body, by the action of heat, requires, according to their several natures, eru cibles of different kinds strong enough to reaist the fire ; made of earthenware, porcelain, or a mixture of clay and powder of black-leail, or of black-lead altogether,
13. Sometimes eruvibles have covers made of earthen. ware, but in other waaea the used inetal must be exposed to a current of airs for this purpose the crucibles are broad and shallow, and are called pupels.
14, Blow-pipes are used for directing tne flame of a candle or lamp against any piece of ore or other substance required to be examined, and when oxygen or hayatrogen FAS is used instead of common air, the heat is most powerful.
15. The various degrees of heat, or atomie motor, which are required for the performance of chemical operations, render it necessary that the clienuist should also be possessed of a furwave,
16. Chemical combinations are more generally in. fluenced by the agency of powers, called by the names of attraction and reputaion, boint in truth consisting of various susceptibilities of motion in the atoms of borlies, and in the columns of the media in which they are placerlo
17.-- When a new substance is produced from the conti bination of two others, the operation is called Sumihenka, When that substance is decoinposel, or resolved into its constituents by the assistance of other obemical agents, the operation is termed Analysis,
18.--Elementary bodies are those which no art of modern ehemistry lias been able to decompose into utler elenienta.
19.-- Atomic motion produced by percussion, by friction, or by transfer, is the cause of all the varieties of lical, tire, and calorie,
20. Tomperature signifies the varied intensity ar via. lence of intestine atomie motion, whichi, ly increasing the distance of the particles or atoma increases the voluure of bodies,
91,--Different hodies change their states at very difes, ferent temperatures or degrees of atomie motion. Thus inereury, which become a solid at about 40e below (e in Fahrenheit, boils at about 100% sulphur, whieb become Hund at 918, boils at b79a, i ether boils at 98.
82.-- Resistence, says Sir Richard Phillips, is a phano. menon of parting with received motion. A body said to be resistou, is merely parting with its motion to the atoma which it encounters in the inedia within which it moves; and, as it continues to part with its motion to the radiating atoms, its genulually diminished energy of motion in, in vulgar language, said to be destroyed by resistance.
22. Tretion, says he, lihe resistance, is a mere phenomenon of parting with motion, but to a fixed body instead of a fluid; and being a variation of percussion, as of transfer of motion without change of place, it produces similar phenomena of intestine atomie motion or hend, which, when continued or accelerated, produces all the os her pheuomena of accelerated atomic inotion or heat.
23. --Crystallization, he says, is a mere effect of partiog 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 puids are einbinations of hrat (or transferred motion) with varinis 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 orygon of the atmosphere uniling with vertain parts of the body
3. T'hat orygen spens to be the acidifying principle: and that all acids are combinations of oxygen with other rebutances ;
4. And that all salts are combinations of an acid with atker aubstances, cattend the base of the sail.
Obs.-SIR HUMPRREY DAVS, 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 alınost infinitely various, and they are in a state of continued alteration. The whole surface of the earth even undergoes modifications. Acted up by moisture and air, it attords the food of plants; an immense number of vegetable productions arise from apparently the same tnaterials; these become the substance of animals; one species of animal matter i aconverted into another; the most perfect and beautiful