Imágenes de páginas
PDF
EPUB

Q. Why does inhaling air rapidly make the body feel warm ?

A. Because more oxygen is introduced into the body; in consequence of which the combustion of the blood is more rapid, the blood itself more heated, and every part of the body is made warmer.

4. Effects of Weather on the Spirits. Q. Why do we feel almost suffocated in a hot cloudy night?

A. Because the heat of the earth cannot escape into the upper region of the air ; but is pent in by the clouds, and confined to the surface of the earth.

Q. Why do we feel sprightly in a clear bright night?

A. Because the heat of the earth can readily escape into the upper regions of the air, and is not confined and pent in by thick clouds.

Q. Why do we feel depressed in spirits in a wet murky day?

A. 1st, Because the air is laden with vapour, and has (proportionally) less oxygen; 2dly, The air being lighter than usual, does not balance the air in our body; and, 3dly, Moist air has a tendency to depress the nervous system.

Q. What is meant by the “air balancing the air in our body?”

A. The human body contains air of a given density; if, therefore, we ascend into rarer air, or descend into denser, the balance is destroyed, and we feel oppressed.

Q. Why do we feel distressed if the air around us is not of the same density as that in our body ?

A. Because if the air be more dense than our body, it will produce a feeling of oppression; if it be less dense, the air in our body will produce a feeling of distension.

5. Air, and its effects on the Body. Q. What are the uses of the oxygen of the air ? A. To support combustion, and sustain life.

Q. What is meant when it is said, that the oxygen of the air “ supports combustion ?”

A. It means this : it is the oxygen of the air which makes fuel burn.

Q. How does the oxygen of the air make fuel burn ?

A. The fuel is decomposed (by heat) into hydrogen and carbon; and these elements combining with the oxygen of the air, produce combustion.

Q. What gas is produced by the combination of carbon and oxygen ?

A. Carbonic acid gas.
Q. What becomes of the hydrogen of the fuel ?

A. The hydrogen of the fuel combines with the oxygen of the air, and forms watery vapour ; but the combination is attended by the production of flame, owing to the very inflammable nature of the hydrogen gas.

Q. What becomes of the nitrogen of the air, amidst all these changes and combinations ?

A. The nitrogen escapes unchanged, to be again mixed with oxygen, and converted into common air.

Q. What is meant when it is said, that oxygen “sustains life ?

A. It means this: if a person could not inhale oxygen he would die.

Q. What good does this inspiration of oxygen do?

A. 1st, It gives vitality to the blood ; and, 2dly, It is the cause of animal heat.

Q. How is food converted into blood ?

A. After it is swallowed, it is dissolved in the stomach into a grey pulp called chyme; it then passes into the intestines, and is converted by the “ bile” into a milky substance called chyle.

[Chyme, pronounce kyme ; chyle, pronounce kyle

each as one syllable.] Q. What becomes of the milky substance called chyle?

A. It is absorbed by the vessels called “lacteals,” and poured into the veins on the left side of the neck.

Q. What becomes of the chyle after it is poured into the veins ?

A. It mingles with the blood, and is itself converted into blood also.

Q. How does the oxygen we inhale mingle with the blood ?

A. The oxygen of the air mingles with the blood in the lungs, and converts it into a bright red colour.

Q. What colour is the blood before it is oxidized in the lungs ?

A. A dark purple. The oxygen turns it to a bright red.

[Oxidized, i.e., impregnated with oxygen.] Q. Why are persons so pale who live in close rooms and cities?

A. Because the blood derives its redness from the oxygen of the air inhaled; but as the air in close rooms and cities is not fresh, it is deficient in oxygen, and cannot turn the blood to a beautiful bright red.

Q. Why are persons who live in the open air and in the country of a ruddy complexion !

A. Because they inhale fresh air which has its full proportion of oxygen ; and the blood derives its bright red colour from the oxygen of the air inhaled.

Q. Why is not the air in cities so fresh as that in the country?

A. Because it is impregnated with the breath of its numerous inhabitants, the odour of its sewers, the smoke of its fires, and many other impurities.

Q. How does oxygen convert the colour of blood into a bright red ?

A. The colouring matter of the blood is formed by very minute globules floating in it; the oxygen (uniting with the coats of these globules) makes them milky; and the dark colouring matter of the blood (seen through this milky coat) appears of a bright red.

Exp. If you put some dark venous blood into a milky glass, and hold it up towards the light, it will appear of a bright florid colour, like arterial blood.

Q. How does the combination of oxygen with the blood produce animal heat ?

A. The principal element of the blood is carbon; and this carbon (combining with the oxygen of the air inhaled) produces carbonic acid gas, in the same way as burning fuel.

Q. What becomes of the nitrogen of the air after the oxygen enters the blood ?

A. It is thrown out from the lungs unchanged by the act of breathing, to be again mixed with oxygen, and converted into common air.

Q. Why does the vitiated air (after the oxygen has been absorbed) come out of the mouth, and not sink into the stomach ?

A. Because a mechanical provision is made in the upper part of the wind-pipe and gullet for this purpose.

N.B.- The lungs are a hollow spungy mass, capable of confining air, and of being dilated by it. They are so situated in the thorax (or chest) that the air must enter into them whenever the cavities of the thorax are enlarged. The process of breathing is performed thus : when we inhale, the thorax (or chest) is expanded ; in consequence of which a Facuum is formed round the lungs, and heavy external air instantly enters (through the mouth and throat) to supply this vacuum.

When we exhale, the thorax contracts again ; in consequence of which, it can no longer contain the same quantity of air as it did before; and some of it is necessarily expelled. When this expulsion of air takes place, the lungs and muscular fibres of the wind-pipe and gullet contract, in order to assist the process.

6. Coal Gas, Safety Lamps, Mines. Q. What is choke-damp?

A. Carbonic acid gas accumulated at the bottom of wells and pits. It is called choke-damp, because it chokes (or suffocates) every animal that attempts to inhale it.

It suffocates without getting into the lungs, by closing the outer orifice spasmodically.

Q. What is marsh-gas or fire-damp ?

A. Carburetted hydrogen gas accumulated on marshes, in stagnant waters, and coal-pits; it is frequently called “inflammable air.”

Q. What is carburetted hydrogen gas ?
A. Carbon combined with hydrogen.

Q. How may carburetted hydrogen gas be procured on marshes ?

A. By stirring the mud at the bottom of any stagnant pool, and collecting the gas (as it escapes upwards) in an inverted glass vessel.

Q. What is coal gas ?
A. Carburetted hydrogen extracted from coals by the heat

Q. Why is carburetted hydrogen gas called fire-damp, or inflammable air?

A. Because it very readily catches fire, and explodes, when a light is introduced into it, provided atmospheric air

of fire.

be present.

Q. Why is carburetted hydrogen gas frequently called marsh gas ?

A. Because it is generated in meadows and marshes from putrefying vegetable substances.

Q. What gas is evolved by the wick of a burning candle ?

A. Carburetted hydrogen gas. The carbon and hydrogen of the tallow combine into a gas from the heat of the flame; and this gas is called carburetted hydrogen, or inflammable air.

Q. Why do coal mines so frequently explode ?

Ă. Because the carburetted hydrogen gas (which is generated in these mines by the coals) explodes when a light is incautiously introduced.

Q. How can miners see in the coal pits, if they may never introduce a light ?

A. Sir Humphrey Davy invented a lantern for the use of miners, called the Safety Lamp, which may be used without danger.

Q. Who was Sir Humphrey Davy ?

A. A very able chemist, born in Cornwall, 1778, and died 1829.

Q. What is a safety lamp?

A. A kind of lantern, covered with a fine gauze wire, instead of glass or horn.

Q. How does this fine gauze wire prevent an explosion in the coal mine?

A. By preventing the flame of the lamp from communicating with the inflammable gas of the mine.

N.B.—The interstices of the gauze wire must not exceed the seventh of an inch in diameter.

Q. Why will not flame pass through very fine wire-gauze !

A. Because the metal wire is a very rapid conductor of heat; and when the flame of gas (burning in the lamp) reaches the wire-gauze, so much heat is conducted away by the wire, that the flame is extinguished.

Q. Does the gas of the coal-pit get through the wire-gauze into the lantern ?

A. Yes; and the inflammable gas ignites, and burns inside the lamp: as soon as this is the case, the miner is in danger, and should withdraw.

Q. Why is the miner in danger, if the gas ignites, and burns in the inside of the safety lamp?

A. Because the heat of the burning gas will soon destroy

« AnteriorContinuar »