A. Because they are mingled together, but the property of each grain remains the _same as it was before_.

Q. _Why is water poured on lime, said to COMBINE with it?_

A. Because the properties, both of the water and the lime, are _altered_ by the mixture: the lime alters the character of the water, and the water alters the character of the lime.

Q. _Do oxygen and nitrogen COMBINE, or only MIX together, in common atmospheric air?_

A. They only _mix_ together, as grains of sand would do, when shaken in a bottle. When oxygen and nitrogen _combine_, they do not const.i.tute _air_, but acid _poisons_.

Q. _Why does LIGHTNING turn BEER SOUR, although contained in a close cask?_

A. If the beer be _new_, and the process of fermentation not complete, lightning will so _accelerate_ the process, as to turn the liquor sour.

Q. _Why is NOT old beer and strong PORTER made SOUR by lightning?_

A. Because the _fermentation is complete_ already; and, therefore, is not affected by electrical influence.

Q. _Why is METAL sometimes FUSED by lightning?_

A. Because the dimension of the metal is _too small_, to afford a path for the electric current.

Q. _Why does LIGHTNING PURIFY the AIR?_

A. For two reasons: 1st--Because the oxygen and nitrogen of the air _combine_,[3] and produce "nitric acid:"

2ndly--Because the agitation of the storm _stirs up the air_.

[3] The oxygen and hydrogen are not _combined_, but simply _mixed_ in the ordinary air; but the lightning causes the mixed elements to _combine_.

Q. _How does the production of nitric acid purify the air?_

A. Nitric acid acts very powerfully in _destroying exhalations_, arising from putrid vegetable and animal matters.

Q. _Why is LIGHTNING more common in SUMMER and AUTUMN, than in spring and winter?_

A. The heat of summer and autumn produces _great evaporation_; and the conversion of _water to vapour_, always develops _electricity_.

Q. _Why does a THUNDER-STORM generally follow very DRY weather, and rarely succeeds continued WET?_

A. The clouds are _always_ charged with electricity; but _dry air_ (being a non-conductor), will not conduct the surplus fluid from the clouds to the earth: so it violently _rends the dry air_ with a flash, in order to relieve the cloud, and reach the earth.

Q. _What is the general DIRECTION of a THUNDER-STORM?_

A. Either from east to west; or else from north to south.

Q. _Why is ELECTRICITY excited by FRICTION?_

A. Electricity, like heat, exists in _all_ matter; but is often in a _latent state_: friction _disturbs_ it, and brings it into active operation. (see p. 31.)

Q. _Why is a TREE sometimes SCORCHED by lightning, as if it had been set on fire?_

A. Lightning scorches it by its own _positive heat_, just the same as fire would.

Q. _Why is the BARK of a TREE often ripped quite off by a flash of lightning?_

A. As the lightning runs down the tree, it develops the latent heat so _rapidly_, that it carries the bark of the tree along with it, while it seeks to escape.

Q. _Why are BOUGHS of TREES broken off by lightning?_

A. The _mechanical force_ of lightning is very great; and when the flash strikes a tree, it will often break off the boughs by the _force_ with which it strikes against it.

Q. _Why is an electric shock felt MOST at the ELBOW JOINT?_

A. Because the path of the fluid is _obstructed by the joint_: and the shock felt at the elbow is caused by the fluid _leaping from one bone to another_.

CHAPTER III.

Q. _What is the third chief source of heat?_

A. CHEMICAL ACTION.

Q. _What is meant by chemical action being the source of heat?_

A. Many things, when their chemical const.i.tution is changed, (either by the abstraction of some of their gases, or by the combination of others not before united,) evolve _heat_, while the change is going on.

Q. _Explain by ill.u.s.tration what you mean._