but being of less specific gravity than the water, will float upon its surface.

Let the tall "hydrometer" glass be thoroughly cleaned and dried; then select a piece of pewter, copper, or glass tube, about two inches longer than the glass, and having a bore about the size of a goose-quill, and if such cannot be obtained, a hollow reed, or even a piece of large pipe vermicelli may be substituted; one end of the tube, whatever be its material, is to be placed at the pipe of a small glass funnel and secured by gluing a strip of calico around it, the object being to elongate the pipe of the funnel, that it may touch the bottom of the "hydrometer glass," in which it is to be placed, as here shown; the globes at the bottom of the glass will be described hereafter.

Fig. 59.

Place half a pint of rain water in one finger glass, and half a pint in another; add to the one as much "White vitriol," i. e., sulphate of zinc, and to the other as much "Blue vitriol," i. e., sulphate of copper, as it will dissolve, or, in other terms, obtain saturated solutions of these substances, which are known to the chemist as "Salts," although they differ from "common salt” in

chemical composition, and all physical properties, save those of solidity and solubility in water.

By stirring these salts, then, from time to time in the course of a few hours, the desired point of saturation will be gained, and it is indicated by a considerable proportion of each remaining undissolved.

Mould three lumps of wax into the size of hazelnuts; take one of these, and introduce into it a few shot, that will render it sufficiently heavy to sink through water, but yet to float upon the solution of "blue vitriol;" this is easily done after a few trials: take another lump, and introduce into it a few more shot, that will render it sufficiently heavy to sink through the solution of "blue vitriol," but yet to float upon the solution of "white vitriol;" then wash these lumps of wax in water and dry them with a cloth.

Make a cork ball, and select a leaden bullet, of the same size as one of the lumps of wax; heat the bullet slightly, and rub a piece of wax upon it to form a thin coating, or it may be "black-leaded."

Place all the lumps of wax, the cork ball, and the bullet at the bottom of the "hydrometer-glass," as shown in the engraving; color about four fluid ounces of strong alcohol of a fine crimson, with a few grains of cochineal; this forms what is called a "tincture," to denote that it is a solution of coloring matter, in spirit or alcohol, instead of in water.

Strain the "tincture" from the dregs, through a piece of fine muslin, and gently pour about half into the funnel; it will descend through the long pipe into the glass, and the cork ball will float on it; next, slowly pour in about the same bulk of water, and the plain lump of wax will rise and float on it; then, with the same precaution,

pour in about the same bulk of the solution of "blue vitriol," and the lump of wax containing the least shot will rise and float on it; proceed similarly with the solution of "white vitriol," and the lump of wax containing the most shot will rise and float on it; the leaden bullet alone remaining; but, lastly, upon pouring in mercury, the bullet will rise and float upon its surface, as buoyantly as the cork upon the tincture or the lumps of wax upon the other liquids. Remove the funnel and the arrangement will present the extraordinary appearance of five distinct liquids contained in one glass, in the exact order of their specific gravities; and five solid masses floating at different heights; the liquids keep so perfectly distinct that a casual observer might think it was a glass, banded, at intervals, with crimson, blue, and silver.

Fig. 60.

The surface of the bullet is covered with wax, or black-leaded, to prevent the lead from dissolving in the mercury, for which it has a strong attraction; and the great specific gravity of the mercury is shown, not only by the lead floating on it, but by its supporting the weight of all the other liquids; some days will elapse before they mingle, and then no repose will cause their separation.

Substances insoluble or nearly insoluble in water, have mostly a greater specific gravity than it; thus as regards the earths, viz., Silica S. G. 2-660, Alumina S. G. 2.000, Lime S. G., 2·300, Magnesia 2·300; and it is on account of the great Specific Gravities of these earths and likewise of their natural compounds, that they chiefly subside with rapidity or precipitate from water when mechanically diffused throughout it by the force of inundations, or floods, the effects of which have engaged our attention at page 140.

But earths and their compounds are not the heaviest solid forms in comparison with water as a standard; the elementary metals best known surpass them all, as the following statement will prove.

Zinc S. G. 7.000, Iron S. G. 7.780, Copper S. G. 8-890, Silver S. G. 10-470, Lead S. G. 11-350, Mercury S. G. 13.500, Gold S. G. 19.25, and Platinum S. G. 21.00, this last metal being the heaviest substance either natural or artificial that the chemist has discovered.

Some idea of the relative Specific Gravities of solids may be gained by the performance of the following simple experiments; take the tare of a tin cup capable of holding about an ounce of rain-water, and then ascertain exactly how many grains this water weighs; it will afford a standard of comparison: pour away the water, dry the cup perfectly, remove all weights excepting those of the tare from the scale, fill the cup with fine Sand, and ascertain its weight; then proceed similiarly with fine filings of the following metals, viz., Tin, Zinc, Iron, and Lead, and it will be discovered, although all their bulks are nearly equal to that of Water, their weights greatly surpass it; and by finding how many times the

weight of the water is contained in each of their respective weights, an approach to their respective Specific Gravities will be obtained.

A more accurate proceeding is to obtain a solid cylinder of sandstone, and of each of the metals, exactly equal in bulk to the capacity of the tin cup; then having ascertained the weight of water that it will hold, to remove the cup and all weights from the scale, and simply to weigh the cylinders in succession, and then calculate how many times the weight of the water is contained in their respective weights; thus their Specific Gravities will directly appear, and will be nearly coincident with those already stated as belonging to these solid

substances.

These remarks regarding Specific Gravity must not be carried further at present; let us return to the fact from whence they emanated, namely, that the Specific Gravity of Water being 1.000, that of Ice is 0.940, or in other words, Ice is lighter than Water.

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Whatever fluctuations may happen in the density of the atmosphere, they produce no fluctuations in the degree of temperature at which liquid water becomes solid ice, or, in more popular terms, the degree at which water freezes; and the Chemist avails himself of this immutable fact, in the construction of the thermometer that we have employed so frequently during this examination of the chemical phenomena of the Four Seasons.

When the bulb and tube of the thermometer are supplied with a proper amount of mercury, it is immersed in melting ice, until the mercury contracts and becomes stationary; a mark is made upon the tube at this point; and whenever the instrument is again exposed to the