DEMONSTRATION APPARATUS FOR THE SIMULTANEOUS PREPARATION OF THE HALOGENS The apparatus herein described possesses great utility in presenting the subject of halogens. A water-bath, three florence flasks, a thistle tube and two three-way stop-cocks are set up as illustrated. Flasks A, B and C are provided with fairly concentrated solutions of a chloride, bromide and iodide, respectively, with the weights of the salts employed in the ratio of the weight of
their molecules. The water-bath is kept a t the boiling point throughout the experiment to maintain a constant and equal temperature. Chlorine is liberated in flask A with the aid of manganese dioxide and sulphuric acid. By proper adjustment of the stop-cock, the gas may be collected a t A'. To demonstrate its ability to replace bromine in compounds, the stop-cock is turned to permit the chlorine to enter flask B. The bromine, which in turn is liberated, may be sampled a t B' either with or without the use of a condenser. By permitting the bromine to pass into flask C, iodine is set free. The apparatus enables the lecturer to demonstrate a common method for the preparation of the. halogens, provides for the collection of specimens of all the halogens (except fluorine), and illustrates their replacement ability. Chlorine is shown in the gaseous phase, bromine in the liquid and
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gaseous phases, while iodine, in the early stages of its liberation may be seen in solution with the undecomposed iodide, in the solid state and, in small quantities, as vapor. Upon continued heating, some of the iodine vapor deposits itself as a solid in tube C' demonstrating sublimation. By changing the order of the halides, it is possible to show the inability of the weaker halogens to replace the stronger members of the group. If the halogens are not collected a t A' and B' and the same cation is present in each of the halides, the experiment may be carried out quantitatively to show, upon evaporation, that the original contents of flask A (as regards the halide only) have been formed in flask B, and likewise, the original contents of flask B formed in flask C. The iodine must be removed by filtration, of course, and any small quantities remaining in solution in C will be volatilized upon evaporation.
