CATECHISM

OF

AGRICULTURAL CHEMISTRY

AND GEOLOGY.

Q. WHAT is agriculture?

A. Agriculture is the art of cultivating the soil. Q. What is the object of the farmer in cultivating the soil?

A. The object of the farmer in cultivating the soil is, to raise the largest crops, at the smallest cost, and with the least injury to the land.

Q. What ought the farmer especially to know, in order that he may attain this object?

A. The farmer ought especially to know the nature of the crops he raises, of the land on which they grow, and of the manures which he applies to the land.

I. OF THE NATURE OF THE CROPS HE RAISES.

Q. Of what parts do all vegetable substances consist?

A. All vegetable substances consist of two parts, one which burns away in the fire, called the organic part, and one which does not burn away, called the inorganic part.

A

Fig. 1.

Here the teacher will burn a bit of straw or wood in the candle, and show that one part burns and that another very small the ash-does not burn

away

part

away.

Q. Which of these two parts is the greater in quantity? A. In all vegetable substances, the organic part is very much the greater.

It

forms from 90 to 99 out of every 100 lbs. of their weight.

Q. Of what elements does the organic part of plants consist?

A. The organic part of plants consists of four elements, known by the names of carbon, hydrogen, oxygen, and nitrogen.

Q. What is carbon?

A. Carbon is a solid substance, usually of a black colour, which has no taste or smell, and burns more or less readily in the fire. Wood-charcoal, lampblack, coke, and black-lead, are varieties of carbon.

The teacher will here exhibit a piece of charcoal and show how it burns in the fire, or in the flame of a candle.

Q. What is hydrogen?

A. Hydrogen is a kind of air or gas which burns in the air as coal gas does, but in which a candle will not burn, nor an animal live, and which, after being mixed with common air, explodes when it is brought near the flame of a candle. It is also the lightest of all known substances.

Here the teacher will take a beer or champaign glass (fig.2), will put into it some pieces of zinc or iron filings, and pour over them a small quantity of oil of vitriol (sulphuric acid) diluted with twice its bulk of water, and cover the glass for a few minutes. On putting in a lighted taper, an explosion will take place. He will then repeat the same Fig. 2.

Fig. 3.

experiment in a phial, into the cork of which he has introduced a common gas jet (fig. 3). After a short time, when the hydrogen gas produced has driven out all the common air from the bottle, a light may be applied to the jet, when the gas will take fire and burn. The cork and jet may now be taken out of the bottle, and a lighted taper introduced into it, when the taper will be extinguished, while the gas itself will take fire and burn at the mouth of the bottle. Lastly, if the teacher possesses a small balloon, he may fill it with the gas by attaching it to the mouth of the

bottle, and may thus show that the gas is so light that it will carry heavy bodies up with it through the air. Q. What is oxygen?

A. Oxygen is also a kind of air, in which a candle burns with great brilliancy, in which animals also can live, and which is heavier than hydrogen or common air. It forms one-fifth of the bulk of the air we breathe.

Fig. 5.

The teacher will here exhibit a bottle of oxygen gas, and show how rapidly and brilliantly a lighted taper burns when introduced into it.

The easiest and least troublesome mode of preparing oxygen gas, is to heat red oxide of mercury in a small retort by means of a spirit lamp, and to collect the metallic mercury as it distils over and trickles down the beak of the retort (fig. 6). This is not so very costly a process as it (Fig. 6.)

appears to be, since there is no loss of any thing. A pound of the red oxide costs 6s. 8d., and gives 14 oz. of metallic mercury, worth 4s. 8d.

Q. What is nitrogen?

A. Nitrogen is also a kind of air differing from both of the other two. Like hydrogen, a taper will not burn nor will an animal live in it, but unlike hydrogen, it will not burn, and it does not take fire when brought near the flame of a candle. It is a little lighter than atmospheric air, of which it forms four-fifths of the bulk.

The teacher will here exhibit a bottle of this gas, and show that a lighted taper is extinguished when introduced into it.

The easiest mode of preparing nitrogen is by mixing together a quantity of sal ammoniac with half its weight of salt-petre, both in fine powder, and heating them in a retort over a lamp. The gas which comes off is collected over water, as shown above (fig. 5).

Q. Do all vegetable substances contain these four elements?

A. No, the greater number contain only three, viz. carbon, hydrogen, and oxygen.

Q. Name some of the more common substances which contain only these three.

A. Starch, gum, sugar, the fibre of wood, oils, and fats, contain only these three elements.

Q. Of what substances does the inorganic part of the plant consist?

A. The inorganic part of plants contains from eight to ten different substances, namely, potash, soda, lime, magnesia, oxide of iron, silica, chlorine, sulphuric acid, or oil of vitriol, and phosphoric acid.