Chlorine : Hydrogen Chloride, Composition

Expt. 18. - Electrolyse hydrochloric acid of specific gravity 1.1 in the apparatus shown in,

Fig: Electrolysis of hydrochloric acid

using electrodes of gas-carbon, since chlorine attacks platinum. The chlorine evolved at the anode at first dissolves in the liquid, but when the latter becomes saturated, nearly equal volumes of hydrogen and chlorine are evolved. These may be recognised by the inflammability of the former, and the action of the latter on a piece of moist litmus paper, which is bleached.

Expt. 19. - Fill the closed limb of the U-tube shown in

Fig: Decomposition of hydrogen chloride by sodium amalgam

with dry hydrogen chloride to the lower stopcock, by admitting the gas through the upper stopcock, and running out dry mercury from the tube. Close the lower stopcock, pour out the mercury, and replace it with liquid sodium amalgam. Open the stopcock, so as to bring the gas in contact with the amalgam, and allow the apparatus to stand. A white crust of sodium chloride is formed, and the volume of the gas, after levelling, is found to be diminished to one-half. Pour mercury into the open limb of the U-tube, and displace the gas through the stopcock. It will be found to be inflammable, and is hydrogen.

Expt. 20. - Fill one half of a strong glass tube, provided with three stopcocks, as shown in,

Fig: Tube for combination of hydrogen and chlorine

with chlorine by passing the gas through whilst the middle three-way stopcock is open to the air. Fill the other half with hydrogen in the same way. In a room with diffused daylight, open the middle stopcock, and allow the gases to mix. After a few hours, the greenish-yellow colour of the chlorine disappears. If one of the end stopcocks is opened under mercury, no gas escapes and no mercury enters, hence the volume is unchanged. If the tube is opened under water, the latter enters and fills the tube. The liquid contains hydrochloric acid.

Expt. 21. - Pass the mixture of hydrogen and chlorine evolved by the electrolysis of hydrochloric acid of specific gravity 1.1

Fig: Filling glass bulbs with a mixture of chlorine and hydrogen

through a strong glass tube fitted with two stopcocks and platinum firing wires.

Fig: Explosion tube for hydrogen and chlorine

The electrolysis should be allowed to proceed for about half an hour before collecting the gas, so as to saturate the liquid with chlorine, and the tube filled in a dark room with a photographic ruby lamp. The tube may be kept wrapped in black paper for a few hours until required. Support the tube in a clamp behind a strong glass screen in a dimly-lighted room, and fire the gas by a spark from a coil. When the tube is cool, open one stopcock under mercury. No gas bubbles out, and no mercury is drawn in, hence the volume is unchanged. Pour a layer of previously boiled water over the mercury and raise the tube so that the open stopcock dips into the water. The gas dissolves practically completely.