748. What is water?

Water is a fluid composed of two volumes of hydrogen to one of oxygen, or eight parts by weight of oxygen to one of hydrogen. It is nearly colourless and transparent.749. Why, if a saucer of water be exposed to the air, will it gradually disappear?

Because water is highly expansive, and rises in thin vapour, when in contact with warm and dry air.

"Behold there ariseth a little cloud from the sea, of the bigness of a man's hand. And it came to pass in the meantime, that the heaven was black with clouds and wind, and there was a great rain."—1 Kings xviii.

750. Why does steam issue from the spout of a kettle?

Because the heat of the fire passes into the water, and drives its atoms apart, making those of them that rise quickly to the surface lighter than the air, upon which they consequently rise.751. Why does water become solid when it freezes?

Because the latent heat of the water passes away from between its atoms into the air; the atoms, therefore, draw closer together.752. Why, if the atoms of water draw closer together when freezing, does ice expand, and occupy greater space than water?

Because, when the atoms of water are congealing, they do not form a compact mass, but arrange themselves in groups of crystal points, which occupy greater space. Water contracts when freezing until it sinks to 40 deg., and then it expands as ice is formed.

32 deg. is said to be the freezing point, but it should be called the frozen point.753. Why does water boil?

Because heat, entering into the lower portions of the water, expands it; the heated portions are then specifically lighter than those that are cooler; the hot water therefore rises upward, and forces the cooler water down.754. What proportion of the earth's surface is covered with water?

There are about one hundred and forty seven millions of square miles of water, to forty-nine and a half millions of square miles of land.755. What is the amount of water pressure?

The pressure of the sea, at the depth of 1,100 yards, is equal to 15,000 lbs. to the square inch.

"But the land, whither ye go to possess it, is a land of hills and valleys, and drinketh water of the rain of heaven."—Deut. xi.

756. What element is the most abundant in nature?

Oxygen, which forms so large a part of water. Of animal substances, oxygen forms three-fourths; of vegetable substances it forms four-fifths; of mineral substances it forms one-half; it forms eight-ninths of the waters and one-fifth of the atmosphere; and aggregating the whole creation, from one-half to two-thirds consists of oxygen.757. In what ways does man use oxygen?

Man eats, drinks, breathes, and burns it, in various proportions and combinations. It is estimated that the human race consume in those various ways 1,000,000,000 lbs. daily; that the lower animals consume double that amount; and that, in the varied works of nature, no less than 8,000,000,000 lbs. of oxygen are used daily.758. Why does water dissolve various substances?

Because the atoms of water are very minute; they therefore permeate the pores, or spaces, between the atoms of those bodies, and overcoming their attraction for each other, cause them to separate.759. Why does hot water dissolve substances more readily than cold?

Because the heat assists to repel the particles of the substance undergoing solution, and gives the water a freer passage between the atoms.760. Why is pump water sometimes hard?

Because, in passing through the earth, it has become impregnated with mineral matters, usually the sulphate and carbonate of lime.761. Why is rain water soft?

Because it is derived from vapours which, in ascending to the clouds, could not bear up the mineral waters with them. It therefore became purified or distilled.762. Why do kettles become encrusted with stony deposits?

Because that portion of the water which is driven off in steam leaves the mineral matters behind; they therefore form a crust around the sides of the kettle.

It is said that if a child's marble be placed in a kettle, it will attract the earthy particles, and prevent the encrusting of the sides of the vessel.

"He gathereth the waters of the sea together as an heap; he layeth up the depth in storehouses."—Psalm xxxiii.

763. Why is it difficult to wash in hard water?

Because the soap unites with the mineral matters in the water, and being neutralised thereby, cannot dissolve the dirt which we desire to cleanse away.764. Why is the sea salt?

Because salt is a mineral which prevails largely in the earth, and which, being very soluble in water, is taken up by the ocean.

Lakes and rivers, also, even those that are considered fresh, hold in solution some degree of saline matters, which they contribute to the ocean.

As, in the evaporations from the sea, the salt remains in it, while the vapours fall as rain, and again wash the earth and carry some of its mineral properties to the ocean, the greater saltness of the sea, as compared with rivers, is accounted for.

By some persons the opinion is entertained that the sea has been gradually getting salter ever since the creation of the world. This, they say, arises from the evaporation of water free from salt, and the returns of the water to the sea, taking with it salt from the land.765. What is the estimated amount of salt in the sea?

The amount of common salt in the various oceans is estimated at 3,051,342 cubic geographical miles, or about five times more than the mass of the mountains of the Alps.766. What is the depth of the sea?

The extreme depth has not, probably, been ascertained. But Sir James Ross took soundings about 900 miles west of St. Helena, whence he found the sea to be nearly six miles in depth. Now, if we take the height of the highest mountain to be five miles, the distance from that extreme rise of the earth, to the known depth of the sea, will be no less than eleven miles.767. Why are the waters of some springs impregnated with mineral matters?

Because the water passes through beds of soda, lime, magnesia, carbonic acid, oxides of iron, sulphate of iron, &c., &c., and takes up in some slight degree the particles of those minerals, according to the proportions in which they abound.

"Who hath measured the waters in the hollow of his hand, and meted out heaven with the span, and comprehended the dust of the earth in a measure and weighed the mountains in scales, and the hills in a balance?"—Isaiah xl.

768. Why does iron rust rapidly when wetted?

Because the water contains a large proportion of oxygen, some of which combines with the iron and forms an oxide of iron, which is rust.769. Why does stagnant water become putrid?

Because the large amount of oxygen which it contains accelerates the decomposition of dead animal and vegetable substances that accumulate in it.770. Is there danger in drinking water on account of the living animalcules which it contains?

No danger arises from the living creatures in water; but putrefactive matters may produce serious diseases.771. What is the best method of guarding against impurities?

By obtaining water from the purest sources, and by filtering it before drinking, by which nearly all extraneous matters would be separated from it.