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ciple is found to apply to all other elementary substances, each having its combining proportion, or chemical equiva lent, from which, or some multiple of which, it never varies.*

4. As we can form no conception of the number of combinations that may arise from sixty-one elements, so we can form no estimate of the number of different compounds to which their union may give rise; for we must remember that a difference in the proportions of the elements-and sometimes a mere difference in the arrangement-may constitute very different things. An instance of this is seen in the composition of vinegar, sugar, alcohol, and starch, neither one of which contains any element not in the others.

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Give form to life, build sea and land.—SCHILLER.

1. The leading characteristics of oxygen are, that it is the supporter of combustion-as fire will not burn without its presence and it is also the life-sustaining element in the air we breathe. When a piece of charcoal, which is pure carbon, is burned in the open air, the combustion consists in the union of the carbon of the charcoal with the oxygen of the

* The following table comprises a list of all the elementary substances now known, the symbols by which they are designated in chemical books, and the equivalents, or parts by weight, in which they unite to form compounds. It must be remembered that the equiv alent numbers express nothing but the relative weights in which the elements unite with each other. Hydrogen is here taken as the standard, to which all the others are referre!. The names of those which are comparatively unimportant are printed in italics.

Metallic Elements. Sym. Equiv. Metallic Elements. Sym. Equiv.
Calcium
Ca. 20.00 Norium..

Ce. 47.00 Osmium....
Cr. 26.70 Palladium
Co. 29.50 Platinum
Ta. 68.80 Potassium.
Cn, 31.70 Rhodium

Non-metallic

Elements.

Sym. Equiv.

No.

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Os. 99.60

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Pd. 53.30

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Pt. 98.70

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K. 39.20

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Rh. 52.20

Phosphorus..

P.

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Bromine

Br. 80.00 Glucinum

G.

4.70 Sodium

Na. 23.00

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air, forming the compound, carbonic acid. When wood is burned, the process and result are the same, with the exception that the wood is not wholly carbon, and the other ingredients appear during the combustion in the form of smoke and ashes. The rusting of metals is a slow combustion, termed oxidation, and whenever oxygen unites with any other element, some degree of heat is evolved in the process.

2. Iron and steel, and other metals, will burn with exceeding brilliancy in oxygen gas; and, what is more strange, the most intense heat known is produced by burning oxygen and hydrogen in the proportions which form water.* Although no two things in nature are more opposite in character than fire and water, yet in this burning process the water is the product of the fire! Oxygen is heavier than common air, and may be poured from one vessel into another; yet it is invisible, inodorous, and tasteless, and can be detected only by its effects upon other bodies.

3. "As a candle burns in oxygen gas with much greater brilliancy and rapidity than in common air, so animals breathe in it with an increase of pleasure; but it excites them, quickens their circulation, throws them into a state of fever, and finally kills them by excess of excitement. They live too rapidly in pure oxygen gas, and burn away in it like the fast-flaring candle."-JOHNSTON.

4. Hydrogen is the lightest and most attenuated form of matter with which we are acquainted, being fourteen and a half times lighter than common air; hence it is the most suitable gas for inflating balloons. Though forming two thirds of the bulk of water and one ninth of its weight, it is highly inflammable when brought in contact with the oxygen of the atmosphere. Hence, when it is found, as often happens, in coal-mines, united with carbon from the coal and with oxygen, the mixture which is known as fire-damp is highly dangerous to life, as it is liable to violent explosions when lighted by accident. Moreover, those who escape the fire are liable to be suffocated by the carbonic acid which it produces.

5. The danger from fire-damp, however, has been in great part removed by the miners' "safety lamp," invented by Sir Humphrey Davy. He found that the flame of a lamp would not ignite bodies through a fine wire gauze; and by inclosing the miners' lamp within this cheap material, he was enabled both to indicate, by its waning light, the presence of a gas which is fatal to life if long respired, and also to guard

*The arrangement for burning oxygen and hydrogen for the purpose of fusing metals, Laelting glass, etc., is called the oxyhydrogen blowpipe.

against the dreadful effects of an explosion. Thousands may attribute their safety to

"That lamp's metallic gauze, That curtain of protecting wire, Which Davy delicately draws

Around explosive, dangerous fire."

6. As intense heat may cause the decomposition of water, and set free both the inflammable hydrogen and the oxygen which it contains, so, when water is thrown on a burning building in such quantity as not to quench the fire, it may add fuel to the flames. "Setting the river on fire" is by no means an impossibility, although it would not prove a very economical fuel.

7. Carbon, found in a solid state in charcoal and in the diamond, and in crystallized form in the latter, unites readily with oxygen to form carbonic acid. With hydrogen it unites to form a numerous class of compounds. It also forms nearly one half of the solid parts of all plants; and hence, in the economy of vegetation, it performs a most important part.

8. As carbonic acid, which is poisonous to animals when breathed in quantities, is produced both by the process of combustion and by the breathing of animals, the atmosphere would soon become unfit for respiration unless nature had provided some way for removing this deleterious compound. This process is performed by growing vegetables, as already explained; and so well do the operations by which this gas is produced and removed harmonize, that it is never found in excess in places left free to the circulation of the air.*

9. Any one who wishes to test the character of carbonic acid may do so by pouring vinegar upon common soda, but he must be cautious about inhaling the fumes which arise. What is very singular about this gas is, that although it can not be taken into the lungs without injury, considerable quantities of it may be swallowed with impunity; for it is this same gas which gives their sparkling briskness to fermented liquors, to soda-water, and to the waters of some mineral springs.

10. Nitrogen, which is known to us only in the form of a gas, is destitute of either taste, smell, or color. It supports neither combustion nor respiration; a lighted taper introduced into it is immediately extinguished, and animals placed within it soon die. Yet it forms nearly four fifths, by bulk,

*For the properties of carbonic acid, and the effects of breathing it, etc., read, pages 51, 55, and 56 of Fourth Reader; its absorption, as food, by vegetables, see p. 208 Fourth Reader; and for the general principles by which nature harmonizes its production and consumption, sce the lesson on "The Aquaria," p. 268 of this Reader.

of the air we breathe; and although it is not known to enter into the composition of any of the great mineral masses of the earth, it forms a considerable part of most animal and some vegetable substances.

11. Nitrogen is remarkable for its negative properties; and as it enters reluctantly into union with most other elementary substances, and is quite prone to escape from them, it forms very unstable compounds. In the decay of animal and vegetable matter it escapes into the air in the form of ammonia, a compound of hydrogen and nitrogen, which is the chief ingredient of all animal and vegetable manures. When united with oxygen in certain proportions, it forms the well known corrosive substance called nitric acid or aqua fortis, an article of great value in the arts.

LES. IX.-CHEMICAL KNOWLEDGE AND THE USEFUL ARTS. SULPHUR AND CHLORINE.

1. As we have not space to treat of all the elementary substances and their combinations, we select here two, sulphur and chlorine, for the purpose of illustrating the bearings of chemical knowledge upon the arts of civilized life.

2. Why has Great Britain imported annually from the vicinity of southern Italy the enormous quantity of 60,000 tons of sulphur? Why have a million and a half dollars in gold, or their equivalent, been exchanged for such a substance as brimstone in a single year? It must be because the English people preferred sulphur to gold. Why such a strange preference the reader may reasonably inquire.

3. It was not to make gunpowder, and friction matches, as might at first be supposed, but to maintain and promote civilization through the medium of some of the most useful arts. Without sulphur the processes of bleaching, dying, metal-refining, soda-making, and electro-telegraphing would cease; and the stock of the druggist, and of the dealer in paints, could not be replenished.

4. Sulphur may well be called the key which opens the door to chemical manufactures. In combination with oxygen, under the name of sulphuric acid, it forms a compound necessary in almost every process of manufacturing industry. Although found principally in volcanic regions, sulphur is present in all soils where turnips, cabbages, or mustard will grow to maturity, as is shown by its presence in the seeds

of such plants. A silver spoon used in preparations of mustard is blackened by the contained sulphur. Sulphur is found also in eggs, as is shown in the same manner..

5. Chlorine is the name of another very important element, which, like sulphur, is extensively used for bleaching purposes, and also for the removal of noxious effluvia. It is obtained pure only in the form of a gas; but with the metals it forms many important combinations. The ocean is its great reservoir, where it combines with sodium to form common salt. One atom, or proportion, of chlorine, combined with one of mercury, forms calomel--a powder well known to those who take "doctors' stuff;" and two atoms of chlorine with one of mercury make that deadly poison called corrosive sublimate. It is well to remember that the white of eggs is an effectual antidote for this poison, if taken in season.

6. Chlorine enters into the composition of many vegetable products; and experiments have shown that the germination of seeds is promoted by its presence. The most explosive substance known is a compound of chlorine and nitrogen; and if the chemical affinity existing between the elements of common table-salt were to be suspended for a moment, the very contents of the salt-cellar might prove fatal to the inmates of a closed room in which such separation of elements should occur.

LES. X.-THE PRINCIPAL METALS: GOLD-SILVER-IRON.

1. THESE are simple elementary substances, so far as is yet known; for all the efforts of chemical art have failed either to decompose them, or to form them by the combination of other elements. Of these, gold is deemed the most precious; as it is not only the most ductile and malleable of all the metals, but, being a very dense, fixed substance, and not liable to changes by exposure to the air, it is well fitted to be used as coin, and hence is in universal demand. Therefore it is that

2.

For gold the merchant plows the main,
The farmer plows the manor.-Burns.

Gold! gold! gold!

Bright and yellow, hard and cold,

Molten, graven, hammered, and rolled,

Heavy to get, and light to hold,

Hoarded, bartered, bought, and sold,

Stolen, borrowed, squandered, doled,

Spurned by the young, but hugged by the old

To the very verge of the church-yard mould;

Pride of many a crime untold;

Gold! gold! gold! gold!

Good or bad a thousand-fold,

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