Exp. 3. Examine the physical properties-colour, appearance, hardness, &c.-of a piece of copper. Examine the physical properties-appearance, liquidity, &c.-of sulphuric acid. The two substances are most distinctly marked off from each other by their physical properties.

Cut the copper into very small pieces, place these in the sulphuric acid, and warm until a part of the copper has dissolved in the acid; pour off the blue coloured liquid into a basin; evaporate the liquid, in the draught cupboard, nearly but not quite to dryness; allow to cool. A blue, crystalline, solid is obtained, very unlike either the copper or the sulphuric acid by the interaction of which it has been produced. This blue solid is called copper sulphate.

Attempt to separate the copper sulphate into its constituents by (a) acting on it with water, it dissolves but is obtained unchanged on evaporating off the water; (b) acting on it with a mixture of alcohol and water, it dissolves but is obtained unchanged when the solvent is removed by evaporation; (c) acting on it with strong alcohol, it remains unchanged.

Now dissolve in water some of the copper sulphate which you have prepared, add a little sulphuric acid, and immerse in the liquid two platinum plates, each of which is connected with a galvanic battery (Fig. 6). The electric current passes

Fig. 6.

from one platinum plate to the other through the solution of copper sulphate. After a short time you notice that the platinum plate connected with the zinc plate of the battery is covered with a reddish solid. Allow the current to pass for

a little time; then remove the platinum plate and examine the red solid deposited on it; so far as you can judge, this solid is copper. That the solid is copper can be proved without doubt; but at present you must be content with such a rough proof as is afforded by comparing, by means of the senses, the red solid you have obtained with the copper given you at the beginning of the experiment.

In this experiment you produced a Compound of copper with sulphuric acid; you failed to separate this into unlike parts by methods which had already succeeded in separating one or two Mixtures into unlike parts; but you separated the Compound into unlike parts, one of which was known to be a constituent of the compound, by using the agency of an electric

current.

Reference to "ELEMENTARY CHEMISTRY." Chap. III.

CHAPTER IV.

CONSERVATION OF MASS OF MATTER.

Exp. 1. Fill a large test tube with water, cover the mouth with the thumb, and invert the tube in a small light basin partly filled with water. The tube should now be quite full of water; air must not be allowed to get in while the tube is being placed in the water in the small basin. If a ring

of thick glass is slipped over the test tube the tube will stand steadily in the basin (Fig. 7). Place the small piece of zinc* given you in the basin, and bring it under the mouth of the tube (s. Fig. 7). Pour a very little concentrated sulphuric acid into a very small beaker. Place the small basin with its contents, and the small beaker containing sulphuric acid, on the pan of a fairly good balance, and counterpoise the whole. Without removing the basin from the balancepan, pour the sulphuric acid into it, and replace the little beaker on the pan of the balance. A chemical change proceeds between the dilute sulphuric acid and the zinc; a gas collects in the tube; this gas is hydrogen. From time to time, as the change proceeds, and again when the change is finished, allow the balance to swing; the mass of the matter in one pan remains equal to that of the counterpoise in the other.

Fig. 7.

New kinds of matter have been produced in this experiment, but the sum of the masses of these is equal to the sum of the masses of the kinds of matter present before the change began.

*Note to Demonstrator.

The piece of zinc should be such that when it dissolves in acid hydrogen is produced sufficient to fill the tube about ths. 08 grams zinc produce about 25-30 c.c. hydrogen.

Exp. 2. Collect carbon dioxide in a perfectly dry test tube (s. Chap. I. Exp. 6). When the tube is full, pour a little concentrated potash solution into it, and instantly cover the mouth of the tube with the thumb; shake briskly; invert the tube under a little water in a basin, and withdraw the thumb; the water rushes into and nearly (or perhaps quite) fills the tube. Carbon dioxide is therefore easily and rapidly dissolved by a concentrated aqueous solution of caustic potash.

You are now given an apparatus formed of two light test tubes and a small piece of fairly wide glass tubing (Fig. 8).

The tube C contains small pieces of solid caustic potash; fill B about ths with a solution of caustic potash (1 part solid potash in 2 parts water, by weight). Place a couple of little bits of marble in A, each about 5 mm. (say in.) diameter; and pour in a very dilute solution of hydrochloric acid to about the height shewn in the figure. Insert the corks in A and B, but arrange the tube d so that it does not dip under the surface of the potash solution in B, and do not place C in connection with B; suspend the apparatus from the hook at the end of one arm of the balance, and place C on the pan of the balance; on the other pan place a counterpoise which is very slightly lighter than the whole apparatus, and allow the balance to swing freely. After a few minutes

the position of the pointer of the balance indicates that the system of tubes has lost weight slightly; the stream of carbon dioxide has swept the air out of the tubes, and some of the carbon dioxide has also passed out of the apparatus. Now adjust the tube d as shewn in the figure, attach B to the small tube t, and arrange the counterpoise so that the pointer indicates that the balance is in equilibrium. Allow the balance to swing, and observe the course of the change. Marble (calcium carbonate) and hydrochloric acid are interacting to produce water, carbon dioxide, and calcium chloride, but everything is retained in the apparatus. The total mass of the matter remains unchanged.

The total mass of matter taking part in a chemical or physical change is constant; the sum of the masses of the different kinds of matter produced in a chemical change is equal to the sum of the masses of the different kinds of matter which by their interaction produced the new kinds of matter. Reference to "ELEMENTARY CHEMISTRY." Chap. IV.

2

M. P. C.