Note 5 — Chapter XI · THE HALOGENS: CHLORINE, BROMINE, IODINE, AND FLUORINE
George Kamensky translation
The reaction of hydrochloric acid upon bleaching powder gives chlorine without the aid of heat, CaCl2O2 + 4HCl = CaCl2 + 2H2O + 2Cl2 and is therefore also used for the preparation of chlorine. This reaction is very violent if all the acid be added at once; it should be poured in drop by drop (Mermé, Kämmerer). C. Winkler proposed to mix bleaching powder with one quarter of burnt and powdered gypsum, and having damped the mixture with water, to press and cut it up into cubes and dry at the ordinary temperature. These cubes can be used for the preparation of chlorine in the same apparatus as that used for the evolution of hydrogen and carbonic anhydride—the disengagement of the chlorine proceeds uniformly.
A mixture of potassium dichromate and hydrochloric acid evolves chlorine perfectly free from oxygen (V. Meyer and Langer).