Spontaneous Inflammability.-The most striking way to show this is as follows. Cut off a small piece with a knife the phosphorus may be held by the fingers on the bench while being cut. Dry it on a cloth or on blotting paper, put it in a dry est tube, and treat it with a little bisulphide of carbon. The phosphorus will at once dissolve. Moisten a piece of blotting paper with the solution. The bisulphide of carbon being very volatile, evaporates in a minute, and leaves the phosphorus spread out over a large surface. The phosphorus will soon take fire, unless the solution were too weak.

It Burns to Phosphoric Acid.—In the middle of a common plate put a porcelain crucible lid, with the handle knocked off, and cover with a bell glass. Let everything be perfectly dry. Put a small piece of dry phosphorus on the crucible lid, touch it with a warmed glass rod to light it, and replace the bell glass. The phosphorus will burn, combining with oxygen, and producing phosphoric acid, which appears in the form of a white smoke, and falls like snow on the plate. When the com

bustion is finished, remove the bell and expose the acid a minute or two to the air, it will attract a quantity of moisture from the air and become wet. (A substance which attracts moisture from the air is called hygroscopic, if in so doing it becomes liquid, it is said to deliquesce.) Also test the acid with litmus paper, which will be turned red.

NITROGEN.

Preparation. Arrange an apparatus like the last, only take a soup plate instead of an ordinary plate, fill it with water, float the lid on a bung,

the top.

and let the bell glass have a stoppered opening at Put in the lid a small piece of dry phosphorus, light it by touching with a warmed glass rod, and cover it with the bell. When the light has gone out, allow the white fumes time to subside into the water; an invisible gas remains, which is nitrogen. The air is a mixture of 4 parts nitrogen and 1 part oxygen. Notice that the water has risen in the bell, showing that a portion of the air has disappeared. Remove the stopper, and introduce a lighted piece of paper, the flame will be extinguished. The nitrogen generally smells of the phosphorus.

To each element is assigned a particular Unit of quantity, and also a Symbol, which represents

that unit.

A Compound is any substance which is not an element.

The Formula of a compound is a collection of symbols which shows the elements present in the compound, and the amounts of those elements; at the same time it represents the Unit of quantity of the compound.

The Unit of a compound is the sum of the quantities represented by the symbols composing

the formula.

Thus-H,O is called the formula of water; HSO, the formula of hydric sulphate; KC1O, the formula of potassic chlorate.

H.O signifies 2 units (2 parts) of hydrogen,

combined with 1 unit (16 parts) of oxygen, making 1 unit (18 parts) of water.

H,SO, signifies 2 units (2 parts) of hydrogen, combined with 1 unit (32 parts) of sulphur, and 4 units (64 parts) of oxygen, making 1 unit (98 parts) of hydric sulphate.

KCIO, signifies 1 unit (39·1 parts) of potassium combined with 1 unit (35.5 parts) of chlorine, and 3 units (48 parts) of oxygen, making 1 ́unit (122-6 parts) of potassic chlorate.

QUESTIONS ON USE OF SYMBOLS.

Given the percentage composition of a compound, to find its formula.

1. The percentage composition of water is

putting H for Hyd.,, and O for Ox.16)

we have H11-11 08:88