Here the teacher may exhibit to his pupils, potash in the form of the common pearl ash of the shops; soda, in that of the common soda of the shops; lime and magnesia, in the forms of quicklime and calcined magnesia; oxide of iron, in the form of rust of iron; silica, in the form of a piece of flint, rock crystal or quartz, (chucky-stone); a bottle of chlorine gas, one of sulphuric acid, (oil of vitriol), and one containing a little phosphoric acid, or burnt bones in which phosphoric acid is present. By placing these substances, or the bottles containing them, before the eyes of the pupils occasionally, they will soon become familiar with their names and with their several qualities. Q. What is potash?

A. The common potash of the shops is a white powder, which has a peculiar taste called an alkaline taste, and which becomes moist, and at last runs to a liquid when exposed for a length of time to the air. It is obtained by washing wood ashes (the ashes left by wood when it is burned) with water, and afterwards boiling the liquid to dryness.

The teacher will here allow his pupils to taste the potash, that they may become familiar with the meaning of the word alkaline as applied to taste.

Q. What is soda?

A. The common soda of the shops is a glassy or crystallized substance, which has also an alkaline taste, but which, unlike potash, becomes dry and powdery by being exposed to the air. It is manufactured from sea salt.

The teacher will show a crystal of the common soda of the shops, and explain the meaning of the word crystallized.

Q. What is lime?

A. Lime or quick-lime is a white earthy substance, which is obtained by burning common limestone in the lime-kiln. It has a slightly burning taste, and becomes hot and slakes when water is poured upon

it.

The teacher will exhibit a piece of quicklime, will allow his pupils to taste it, and will pour water upon it, that it may fall to powder. They will thus become familiar with the word slake.

Q. What is magnesia?

A. Magnesia is the white powder sold in the shops under the name of calcined magnesia. It has scarcely any taste, and is extracted from sea water and from some kinds of limestone rock.

Q. What is iron ?

A. Iron is a hard bluish-gray metal, which is manufactured in large quantities in our iron-works, and is used for a great variety of useful purposes.

The teacher will here explain the word metal, by showing that such common metals as iron, copper, lead, silver, and gold have a lustre, weight, and malleability not possessed by wood, stones, and other substances to which the name of metals is not applied.

Q. What is oxide of iron?

A. When polished iron is exposed to the air it gradually becomes covered with rust. This rust consists of the metal iron, and of the gas oxygen which the iron has attracted from the air, and hence it is called an oxide of iron.

The teacher will explain more fully, that, when metals combine with oxygen, they form new substances, to which the name of oxides is given, and illustrate this by a reference to the red oxide of mercury, which, by the

heat of the lamp, he had resolved or decomposed into oxygen gas and metallic mercury (see fig. 5).

Q. What is silica?

A. Silica is the name given by chemists to the substance of flint, of rock-crystal, and of sandstones. Q. What is chlorine?

A. Chlorine is a kind of air which has a greenishyellow colour, and a strong suffocating smell. A taper burns in it with a dull smoky flame. It exists in common salt in large quantity.

The teacher will exhibit a bottle of this gas, and may advert to the remarkable fact that this very noxious gas should form more than half the weight of the very wholesome substance common salt. It is readily made by pouring muriatic acid on black oxide of manganese in a retort, and applying a gentle heat. It should be collected over hot water.

Q. What is sulphuric acid or oil of vitriol?

A. Sulphuric acid or oil of vitriol is a very sour burning oily liquid, which is manufactured from burning sulphur (brimstone). It exists in common gypsum, in alum, and in Glauber and Epsom salts.

The teacher will here exhibit oil of vitriol, and show that when a piece of straw is put into it, it is charred or burned black. He will also exhibit gypsum, alum, Glauber and Epsom salts, and show, that, though the sulphuric acid exists in them, they have none of its burning properties.

Q. What is phosphoric acid?

A. Phosphoric acid is also a very sour substance, which is made by burning phosphorus in the air. It exists in large quantity in the bones of animals.

Fig. 7.

If the teacher possess any phosphorus, he may here show how it burns with white fumes in the air, and may collect these white fumes which are phosphoric acidby holding over them a cold glass or metal plate, or he may simply burn the phosphorus in a little cup under a tumbler (fig. 7).

Q. Are all these substances to be found in the inorganic part of plants?

A. Yes, they are to be found in the ash of all our usually cultivated plants.

Q. Do all plants leave the same quantity of ash when burned?

A. No. Some leave much more ash than others. Thus 100 lbs. of hay leave 9 or 10 lbs. of ash, while 100 lbs. of wheat leave less than 2 lbs. of ash.

Q. Does the ash of different plants contain all these substances in the same proportion?

A. No. They exist in different proportions in the ash of different plants-the ash of wheat, for example, contains more phosphoric acid than that of hay, while that of hay contains more lime than the ash of wheat.

II. OF THE ORGANIC FOOD OF PLANTS.

Q. Do plants require food as animals do? A. Yes, all plants require constant supplies of food in order that they may live and grow.

Q. Where do plants obtain their food?

A. They obtain it partly from the air and partly from the soil.

Q. How do they take in their food?

A. They take it in by their leaves from the air, and by their roots from the soil.

Q. Do plants require two distinct kinds of food? A. Yes, they require organic food to support their organic part, and inorganic food to support their inorganic part.

Q. Whence do they obtain their organic food? A. They obtain their organic food partly from the air and partly from the soil.

Q. Whence do they obtain their inorganic food? A. They obtain their inorganic food wholly from the soil in which they grow.

Q. In what form do plants take in organic food from the air?

A. In the form chiefly of carbonic acid gas.

Q. What is carbonic acid gas?

A. It is a kind of air, which has no colour, but has a peculiar smell. Burning bodies are extinguished in it, and animals die, and it is heavier than common air. It causes the boiling up of soda water, and the frothing of beer, and forms nearly half the weight of nearly all limestone

Fig. 8.

rocks.

Here the teacher will prepare carbonic acid gas, by pouring dilute muriatic acid (spirit of salt) upon bits of limestone in a tall covered beer glass (as in fig. 2) -show that a burning taper is extinguished by it; but that it does not, like hydrogen, take fire itself; that it is so heavy, that it may be poured from one glass to another (fig. 8); and that,

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