SALINE MATTERS FROM THE SEA.

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ing matters give off. It is continually rising, therefore, into the atmosphere from many parts of the earth's surface. It has consequently been found in very minute quantity in the air, wherever it has been sought for. Some, therefore, deem

In this respect, how

it an essential constituent of our air. ever, it must be distinguished from nitric acid, which we know to be produced in the atmosphere itself by purely physical causes, and to be altogether independent of the previous existence of life. It is possible, as I have elsewhere shown, that ammonia may be so produced also; in which case we might not only acknowledge it for an essential constituent of the atmosphere, but discover in its existence, and constant reproduction there, a wise provision for the maintenance of vegetable growth.

Further, from the ever-moving sea, the winds which raise it into rolling waves, and lash it into foam, sweep upwards the light spray, and mingle it with the rushing air. Thus, far inland and over high mountains, the salty particles are carried, and all the contents of sea water are mingled with the universal atmosphere. Hence the host of foreign substances which must float around us, commingled with those which we know to be absolutely necessary to the maintenance of animal and vegetable life, is almost inconceivable.

The accumulation of all these foreign matters in the air would, in course of time, render it unwholesome to animal life-perhaps unfit for the healthy development even of vege table forms. But the waters of heaven, as I have described, ascend and descend continually to wash and purify it. They serve as a natural conservative check.

Thus simple as the air appears, its scientific history as a whole is somewhat complicated. The adjustment of its constituents involves many interesting particulars, and the ar

* Lectures on Agricultural Chemistry and Geology, second edition, p. 288.

rangements by which the constant presence of its essential constituents is secured, both in kind and quantity, are very numerous; yet we cannot fail to perceive both a physical beauty, and a wise contrivance in them all.

CHAPTER II.

THE WATER WE DRINK.

Importance of water in nature.-Composition of water.-Hydrogen gas; how prepared; the lightest of known substances, and an inflammable gas; exists in nearly all combustible substances; is always converted into water when these substances are burned. In water hydrogen is combined with oxygen.-What is meant by a chemical combination.-Water without taste and smell; importance of this.-Cooling property of water.-Relation of water to other liquids.-It dissolves many solid substances; hence natural water never pure.-Quantity of mineral matter in some known river, spring, and sea waters.-Composition of the solid matter in sea water; in the Thames water at Kew; and in that of the Kent Water Company.-Limo held in solution in water by carbonic acid.-Why calcareous waters incrust their channels, petrify, and deposit sediments in boilers.-Impurity of spring waters in large towns, about farmhouses, and near graveyards.-Composition of well water from Highgate Hill.-Well waters in the dunes of Bordeaux; their analogy to the waters of Marah.-Water absorbs its own bulk of carbonic acid at all pressures. -How this explains the liveliness of champagne and soda-water, the bursting of bottles, the briskness and deadness of beer, &c.-Excess of oxygen in the air contained in water; importance of this to the lives of fishes-More oxygen near the surface of the sea.-Why air obtained from snow contains less oxygen.

THE water we drink is next in importance to the air we breathe. It forms three-fourths of the weight of living animals and plants, is the most abundant substance we meet with on the face of the earth, and covers, to an unknown depth, at least three-fourths of its entire surface.

Pure water consists of two stances,* oxygen and hydrogen.

simple or elementary subThe former of these exists

* By simple or elementary substances, chemists understand such as cannot by any known means be resolved or split up into more than one: sulphur, phosphorus, gold, silver, iron, &c., are examples of such simple substances.

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also in common air, and has been described in the previous chapter.

Hydrogen is a kind of air or gas which, when pure, is without colour, taste, or smell. It differs, however, from all the three gases (oxygen, nitrogen, and carbonic acid) described in the preceding chapter; first, in being the lightest of all known substances; and, second, in taking fire, and burning in the air when a lighted taper is brought near it.

Fig. 7.

It is readily prepared by putting a few pieces of metallic zinc or iron into a bottle or flask, and pouring over them a quantity of oil of vitriol (sulphuric acid) diluted with twice its weight of water. When a sufficient quantity of the gas has been produced to drive out the common air from the bottle, a gas jet-burner, or a bit of glass tube, or of a tobacco pipe thrust through a cork, may be put into the mouth of the bottle, when a jet of gas will issue which may be lighted by a taper. It burns with a very pale flame. When a perfectly dry, cool, glass tumbler or bottle is held over the flame (fig. 7), dew will be seen to condense on the inner side of the glass, which will

gradually collect into little visible globules, and will finally trickle down in the form of drops of pure water. This water is formed by the burning of the hydrogen from the bottle in the oxygen of the air. During this burning it combines with the oxygen, and water is produced. The extreme lightness of the hydrogen may be shown by extinguishing the gas, and causing it to ascend into a small

LIGHTNESS OF HYDROGEN GAS.

Fig. 8.

empty balloon placed over the jet (fig. 8). When the balloon is full of gas it will readily ascend, showing not only that the hydrogen is lighter than common air, but that it is so much lighter as to be able to raise heavy bodies through the air along with it. It is to the lightness of this gas that we owe the power of travelling through the air in ordinary balloons.

Hydrogen exists in a great many other substances besides water-in bituminous coal, in wood, in oils and fats, in coal gas, and in nearly all combustible substances; but whenever it is completely burned in the air, water is formed by its union with oxygen, as in the burning of the simple jet above described. Thus, in nearly all cases of combustion, water is one of the substances produced, though it generally rises into the air in the form of invisible vapour.

Water thus formed consists of oxygen and hydrogen, in

-or every 9 lb. of pure water contain 8 lb. of oxygen and 1 lb. of hydrogen.

In atmospheric air, as we have seen, there are at least

Such little balloons, made of thin membranes, are sold by the opticians.