platinum foil 2 in. by 1/8
in. into each hole so that 1/2 in. projects above and below. Insert a
tight plug beside each strip, thus holding it fast and making the
stopper watertight. Insert the stopper into the neck of the jar. Pour
into the vessel thus formed enough water to cover the platinums, and add
a few drops of sulphuric acid. Touch the wires from the battery to the
lower ends of the strips. Note bubbles of gas arise from the platinums.
These may be collected in test-tubes and found by test to be oxygen and
hydrogen.

2. Fasten a strip of platinum 1 in. by 1/8 in. to each wire from the
battery and dip these into some acidulated water contained in a tumbler.
The decomposition of the water into two gases can be seen, but the gases
cannot be collected so readily as in 1 above. Bits of electric light
carbon will do instead of platinum if the current is not too weak.

PNEUMATIC TROUGH

When oxygen or other gas is to be collected over water, use a milk pan
or similarly shaped vessel.

SPIRIT-LAMP

Use an ink-bottle to contain the alcohol and several strands of string
for the wick; make a hole in a piece of tin and draw the wick through;
then let the tin rest on the neck of the bottle to support the wick.

BAROMETER

A siphon barometer takes less mercury than a cistern barometer. To the
open end of the barometer tube attach a piece of strong rubber tubing 4
in. long and to this a piece of glass tubing 3 in. long. Fill the tube
thus formed with mercury to within 3 in. from the top. Holding the short
glass tube open end up, turn the long tube closed end up. (A tube of 1/8
in. bore needs only one quarter of the mercury required to fill a tube
1/4 in. bore.)

HYGROMETER

For a hygrometer, suspend two dairy thermometers side by side against
the wall, cover the bulb of one with thin muslin, and let the muslin
hang down and dip into water in some small vessel placed about three
inches below the bulb on a little shelf.

HINTS

To avoid explosions, a spirit-lamp should be kept filled.

Toy rubber balloons answer well for sheet rubber.

Red ink makes good colouring matter.

Make touch-paper by soaking any porous paper in a solution of saltpetre,
and drying it.

Instead of bending glass tubes, join them with rubber tubing.

To make a test-tube holder, fold a sheet of paper until it is about half
an inch wide and wrap this around the tube.

To bend glass tubing, hold in the flame of the spirit-lamp and rotat