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 constitute 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 constitution 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 illustration what you mean.
A. Water is cold, and sulphuric acid is cold; but if these two cold liquids be mixed together, they will produce boiling heat.
Q. Why will cold water, mixed with sulphuric acid, produce heat?
A. Because water (being lighter than sulphuric acid), is condensed by the heavier liquid; and its heat is squeezed out, as water from a sponge.
Q. Why does cold water, poured on lime, make it intensely hot?
A. The heat is evolved by the chemical action, produced by the cold water combining with the lime.
Q. Where does the heat come from?
A. It was in the water and lime before; but was in a latent state.
Q. Was there heat in the cold water and lime, before they were mixed together?
A. Yes. All bodies contain heat; the coldest ice, as well as the hottest fire.
Q. Is there heat even in ice?
A. Yes. But it is latent, (i.e. not perceptible to our senses).[4]
[4] Latent, from the Latin word, Lateo, (to lie hid.)
Q. How do you know there is heat, if you cannot perceive it?
A. Thus:—Ice is 32° by the thermometer; but if ice be melted over a fire, (though 140° of heat are thus absorbed,) it will feel no hotter than it was before. (i.e. it will be only 32°, and not 172°)[5].
[5] 32°, i.e. 32 degrees; 140°, i.e. 140 degrees, &c.
