Q. _What are the peculiar characteristics of hydrogen gas?_

A. Though this gas _itself_ will _burn_, yet a candle will _not_ burn when immersed in it; nor can an animal live in it. Hydrogen gas is the lightest of all known substances.[7]

[7] Hydrogen gas may be made thus:--Put some pieces of zinc or iron filings into a gla.s.s: pour over them a little sulphuric acid (vitriol), diluted with twice the quant.i.ty of water; then cover the gla.s.s over for a few minutes, and hydrogen gas will be given off.

EXP. If a flame be put into the gla.s.s, an EXPLOSION will be made.

If the experiment be tried in a phial, which has a piece of tobacco-pipe run through the cork; and a light held a few moments to the top of the pipe, a FLAME will be made.

If a balloon be held over the phial, (so that the gas can inflate it,) the balloon will ascend in a very few minutes.

Q. _What is OXYGEN?_

A. A gas, much heavier than hydrogen; which gives brilliancy to flame, and is essential to animal life.[8]

[8] Oxygen gas is much more troublesome to make than hydrogen. The _cheapest_ plan is to put a few ounces of manganese (called the black oxide of manganese) into an iron bottle, furnished with a bent tube; set the bottle on a fire till it becomes red hot, and put the end of the tube into a pan of water. In a few minutes, bubbles will rise through the water; these bubbles are oxygen gas.

These bubbles may be collected thus:--Fill a common bottle with water; hold it topsy-turvy over the bubbles which rise through the pan, but be sure the mouth of the bottle be held _in the water_. As the bubbles rise into the bottle, the water will run out; and when all the water has run out, the bottle is full of gas. Cork the bottle while the _mouth remains under water_; set the bottle on its base; cover the cork with lard or wax, and the gas will keep till it be wanted.

N. B. The _quickest_ way of making oxygen gas, is to rub together in a mortar half an ounce of oxide of copper, and half an ounce of chlorate of pota.s.sa. Put the mixture into a common oil flask, furnished with a cork which has a bent tube thrust through it. Heat the bottom of the flask over a candle or lamp; and when the mixture is red hot, oxygen gas will be given off. Note--the tube must be immersed in a pan of water, and the gas collected as before.

(Chlorate of pota.s.sa may be bought at any chemist's; and oxide of copper may be procured by heating a sheet of copper red hot, and when cool, striking it with a hammer: the scales that peel off, are oxide of copper.)

EXP. Put a piece of red hot charcoal, (fixed to a bit of wire,) into your bottle of oxygen gas; and it will throw out most dazzling sparks of light.

Blow a candle out; and while the wick is still red, hold the candle (by a piece of wire,) in the bottle of oxygen gas; the wick will instantly ignite, and burn brilliantly.

(Burning sulphur emits a _blue_ flame, when immersed in oxygen gas.)

Q. _What is NITROGEN?_

A. Nitrogen is another invisible gas. It _will not_ burn, like hydrogen; and an animal cannot live in it: it abounds in animal and vegetable substances, and is the chief ingredient of the common air.[9]

[9] Nitrogen gas may easily be obtained thus:--Put a piece of burning phosphorus on a little stand, in a plate of water; and cover a bell gla.s.s over. (Be sure the edge of the gla.s.s stands _in the water_.) In a few minutes the air will be decomposed, and nitrogen alone remain in the bell gla.s.s.

(N.B. The white fume which will arise and be absorbed by the water in this experiment, is phosphoric acid; i. e. phosphorus combined with oxygen of the air.)

Q. _Why is there so much nitrogen in the air?_

A. In order to _dilute_ the oxygen. If the oxygen were not thus diluted, fires would burn out, and life would be exhausted too quickly.

Q. _What three elements are necessary to produce COMBUSTION?_

A. Hydrogen gas, carbon, and oxygen gas; the two former in the _fuel_, and the last in the _air_ which surrounds the fuel.

Q. _What causes the combustion of the fuel?_

A. The hydrogen gas of the fuel being set free, and excited by a piece of lighted paper, instantly _unites_ with the _oxygen of the air_, and makes a yellow flame: this flame heats the _carbon of the fuel_, which also unites with the oxygen of the air, and produces _carbonic acid gas_.

Q. _What is carbonic acid gas?_

A. Only carbon (or charcoal) combined with oxygen gas.

Q. _Why does FIRE produce HEAT?_

A. 1st--By liberating _latent heat_ from the air and fuel: and

2ndly--By throwing into _rapid motion_ the _atoms of matter_.

Q. _How is latent HEAT liberated by COMBUSTION?_

A. When the _oxygen_ of the air combines with the _hydrogen_ of the fuel, the two gases _condense into water_; and latent heat is _squeezed out_, as water from a sponge.

Q. _How are the ATOMS OF MATTER DISTURBED by COMBUSTION?_

A. 1st--When _hydrogen_ of fuel and _oxygen_ of air _condense into water_, a _vacuum_ is made; and the air is disturbed, as a _pond_ would be, if a pail of water were taken out of it: and

2ndly--When the _carbon_ of fuel and _oxygen_ of air _expand into carbonic acid gas_, the air is _again_ disturbed, as it would be by the explosion of _gunpowder_.

Q. _How does fire condense HYDROGEN and OXYGEN into WATER?_

A. The _hydrogen of fuel_ and _oxygen of air_ (liberated by combustion) combining together, _condense into water_.

Q. _How does fire expand CARBON into CARBONIC ACID GAS?_

A. The _carbon of fuel_ and _oxygen of air_ (combining together in combustion) expand into a gas, called _carbonic acid_.

Q. _Why is a FIRE (after it has been long burning) RED HOT?_

A. When coals are heated _throughout_, the carbon is so completely mixed with the oxygen of the air, that the _whole surface is in a state of combustion_, and therefore _red hot_.

Q. _In a BLAZING fire, why is the UPPER surface of the COALS BLACK, and the LOWER surface RED?_

A. Carbon (being very solid) requires a great degree of heat to make it unite with the oxygen of the air. When fresh coals are put on, their _under_ surface is heated before the upper surface; and one is _red_ (or in a state of combustion), while the other is _black_.