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LESSONS ON SPECIFIC SUBJECTS.

CHEMISTRY.

1. ELEMENTARY AND COMPOUND MATTER.

1. Matter is divided into two kinds, elementary and compound, the former including all substances which consist of only one thing; the other, all those whose particles or atoms possess different properties—that is, are of different kinds. When a chemist takes a piece of marble and analyses it—that is, separates it into the different bodies of which it is made up-he finds that it consists of a bright yellow metal, called calcium; an invisible gas, called oxygen; and carbon, or charcoal. It is, therefore, a compound substance; that is, one made up of several things. But if he take a piece of iron, or gold, and try to analyse it, he can find nothing but iron or gold; there is nothing else in it; it is a simple, or elementary body. * It consists of just one thing; the most searching tests finding not the least particle of anything but iron in the one, or of anything in the other but gold.

2. Before modern chemistry discovered the way to analyse things, it was thought that there were four elements-fire, air, earth, and water-but not one of these is really an element; for chemistry has shown that fire is an effect, not a substance; and that air, earth, and water are not simple but compound bodies.

3. There are, altogether, about sixty-three elementary substances, by the combination of some or other of which, in different proportions, and under different conditions, all things in nature are formed. They consist of four gases-oxygen, hydrogen, nitrogen, and chlorine; one liquid, bromine; eight solid substances that are not metallic-iodine, fluorine, carbon, sulphur, phosphorus, arsenic, silicium, and boron, and include all the metals, which are fifty-one in number, of which twenty-three are more or less abundant, and twenty-eight are mostly very rare, and of very little or of no practical value.

4. A few examples of substances obtained by changes and combinations of others, and thus forming what are called compound substances, may be useful.

(1.) There is a substance called hy-dro-chlo-ric acid, which is of

Compound is from con and pono, Latin, to put together. Elementary is from elementum, Latin, a first principle-that of which all things else are made, and into which they may be resolved.

great value in medicine and in chemical operations, and which, when mixed with another acid (nitric) forms what is called "aqua regia," or royal water, used for dissolving gold. This substance is obtained by putting together in a large flask equal weights of common salt and of sulphuric acid—that is, vitriol,-diluted with a third part of its weight of water. When this mixture is heated, a gas begins to rise from it freely, and this gas, after being purified by passing through a bottle with a little water in it, is carried by a glass tube into a bottle three-fourths full of water. By this water, 480 times its own bulk of the gas is absorbed, with the effect of increasing the volume of the water one-third, and a colourless liquid, which is hydrochloric acid, is the result. Now, how is this new substance produced? Let me tell you. Common salt is known to chemists as the chloride of sodium—that is, it is made up of a metal called sodium, and a gas called chlorine. Water is formed of eighty-nine parts of the gas called oxygen, to eleven of the gas called hydrogen. Now, when you mix the salt and the sulphuric acid diluted with water, the sulphuric acid, or vitriol, takes all the sodium of the salt to itself, and the hydrogen which is in the water joins itself to the chlorine in the salt, and makes hydrochloric gas, which, again, becomes hydrochloric acid when passed into water and absorbed by it, as we have seen. The water and the salt are, thus, decomposed-that is, separated into the separate elements of which they are formed, and they then exchange, each, one of its parts, and, by doing so, form a third substance wholly different from either. Hydrochloric acid is also formed by the action of sunlight, for if a mixture of equal volumes of hydrogen and chlorine gases be exposed to the sun, the two bodies unite with violence, and form hydrochloric acid.

(2.) Water is formed by the union of two gases, as has been said. This is seen if a current of galvanic electricity be passed through water which has a little acid in it, the poles of the battery being so arranged that plates of a metal called platinum pass into two tubes at each pole of the battery. It will be found that the tube over the one pole (the negative one) will be filled with gas, while that over the other pole (the positive) is half filled. On testing these gases, that in the full bottle is seen to be hydrogen, while that in the half-full bottle is pure oxygen; these two gases having been formed by the decomposition of the water. Nor is this all; by exploding carefully measured proportions of the two, water may be formed, thus showing that it consists of these two as its two component parts.

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(3.) If a small quantity of what is called the "red oxide of mercury" be put into a glass tube and heated over a spirit-lamp, it will soon grow darker in colour, then lessen in bulk, and by-and-by disappear altogether, while, at the same time, a shining metallic brightness, like that of a mirror, is formed on the cooler parts of the tube. This, when touched with a glass rod, will run into globules of quicksilver, or mercury. If, now, a lighted match be put into the tube, it will burn more brightly than it did in the air, proving that some gas has been formed during the experiment, and this gas will be found to be oxygen. The weight of the mercury formed in the tube, and of the oxygen thus obtained, if tested, will be found exactly that of the oxide of mercury first put in; and thus it is clear that that substance was really a combination of the metal (mercury) and the gas (oxygen), which are two simple bodies or elements.

(4.) If you expose a piece of iron in clear dry air, it remains unchanged; but if the air be damp, or if you wet the iron, every one knows that it grows red and rusty. The reason of this is: the iron decomposes the water with which it thus comes in contact, and unites itself to the oxygen in it, becoming rust, so far as it Rust is, thus, the oxide of iron, or a compound of oxygen

does so.

and iron.

(5.) The means by which the chemist analyses bodies—that is, breaks them up into their parts, and finds out whether they are simple or compound-are, as these illustrations show, various. Heat is one of the most common, for nearly all substances of vegetable or animal origin may be shown to be compound by simply heating them. The case of the analysis of oxide of mercury, though it is a metallic substance, was an illustration of this. Electricity is another means, as we saw in the case of water. Light, also, and other influences, decompose many bodies; but the most powerful agency is what is called Chemical Affinity-that is, the property by which certain substances tend to unite with other substances when they come in contact, and thus to form new combinations. It is sometimes called Chemical Attraction, because it is a force which causes the particles of substances different from each other to meet in such a way as to form entirely new substances. As we have seen, the union of the metal sodium-which burns if it be put on the surface of water-with chlorine, a suffocating gas, makes common salt, a substance which is not the least like either sodium or chlorine gas. The burning of the metal sodium is another illustration of this law of chemical affinity or

attraction, which is of such endless use in helping us to find out the composition of bodies. Sodium has such an affinity for oxygen, that when a piece of it is put on the surface of water, it instantly catches fire, decomposing the water, and uniting so violently with the oxygen in it, as to cause combustion, while it leaves only hydrogen-thus showing of what water really consists.

These are the chief means used for chemical analysis, and all substances which show the presence of more than one thing-as, for instance, water, which consists of two things; sugar, which consists of three; or pure white of egg, which consist of six things -are called compound; while those which consist of only one thing are called elements, or simple bodies.

GREECE.-Lord Byron.

HE who hath bent him o'er the dead,
Ere the first day of death is fled-

Before decay's effacing fingers

Have swept the lines where beauty lingers;

And marked the mild angelic air,

The rapture of repose that's there,
The fixed yet tender traits that streak
The languor of the placid cheek,
And-but for that sad shrouded eye,

That fires not-wins not-weeps not-now,
And but for that chill, changeless brow,
Where cold obstruction's apathy
Appals the gazing mourner's heart,
As if to him it could impart

The doom he dreads, yet dwells upon―
Yes, but for these, and these alone,
Some moments, ay, one treacherous hour,
He still might doubt the tyrant's power;
So fair, so calm, so softly sealed,
The first-last look-by death revealed!
Such is the aspect of this shore-

'Tis Greece-but living Greece no more!

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But when he called on Nelly Gray,
She made him quite a scoff;
And when she saw his wooden legs,
Began to take them off!

"Oh, Nelly Gray! oh, Nelly Gray!
Is this your love so warm?
The love that loves a scarlet coat
Should be more uniform!"

Said she, "I loved a soldier once,
For he was blithe and brave;
But I will never have a man

With both legs in the grave!

"Before you had those timber toes,
Your love I did allow,

But then, you know, you stand upon
Another footing now!"

"Oh, Nelly Gray! oh, Nelly Gray!

For all your jeering speeches,

At duty's call I left my legs,

In Badajos's breaches!"

"Why then," said she, "you've lost the feet

Of legs in war's alarms,

And now you cannot wear your shoes

Upon your feats of arms!"

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