PART II.

AIR.

CHAPTER XVIII.

Q. _Of what is atmospheric AIR composed?_

A. Princ.i.p.ally of two gases, _oxygen_ and _nitrogen_; mixed together in the following proportion: viz. 1 part of oxygen, to 4 parts of nitrogen.

Q. _What are the uses of the OXYGEN of the air?_

A. It is the _oxygen_ of the air which _supports combustion_, and _sustains life_.

Q. _What is meant when it is said, that the OXYGEN of the air "SUPPORTS COMBUSTION?"_

A. It means this; that 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 being decomposed (by heat) into _hydrogen_ and _carbon_; the _carbon combines with the oxygen of the air_, and produces _combustion_.

Q. _What does the combination of carbon and oxygen produce?_

A. The _carbon of the fuel_ combining with the _oxygen of the air_ makes CARBONIC ACID GAS. (_see pp. 36, 37_).

Q. _What becomes of the HYDROGEN of the FUEL?_

A. Hydrogen (being very inflammable) _burns with a blaze_, and is the cause of the _flame_ which is produced by combustion. (_see p. 34_).

Q. _What becomes of the NITROGEN of the air, amidst all these changes and combinations?_

A. The _nitrogen of the air escapes_, and is _absorbed by the leaves_ of gra.s.s, trees, and various other vegetables.

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

2ndly--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_; it then pa.s.ses into the intestines, and is converted by the "bile" _into a milky substance_ (called _chyle_).

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 then _mingles with the blood_, and is itself _converted into blood_.

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 oxydized in the lungs?_

A. _A dark purple._ The oxygen turns it to _a bright red_.

Q. _Why are PERSONS so PALE who live in CLOSE ROOMS and CITIES?_

A. 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. As the blood derives its bright red colour from the _oxygen_ of the air inhaled, therefore, country-people (who inhale _fresh air_) are more ruddy than citizens.

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.