If chlorine is passed into water cooled in ice, almost white crystals separate. This substance, discovered by Berthollet in 1785, is chlorine hydrate: its composition has been variously stated to be Cl2,ioH2O (Faraday, 1823), Cl2,8H2O (Rooze-boom, 1884), Cl2,7H2O (de Forcrand, 1902) and, according to Bouzat and Azinieres (1923), Cl2,6H2O if prepared in presence of liquid chlorine. When gently warmed, the crystals melt with effervescence, and chlorine is evolved. If the experiment is performed in the dark, the gas after drying is perfectly pure (Harker, 1892).
Expt. 15. - If crystals of chlorine hydrate are sealed up in one limb of a strong bent tube, and the other limb is cooled in ice and salt,  | Fig: Liquefaction of chlorine |
liquid chlorine distils into the cooled part of the tube when the other is warmed to about 30°. These tubes must not be exposed to light for any length of time, otherwise oxygen is formed, which bursts them.
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