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FUN with the HALOGENS - Popular Science, 1939...

WHENEVER the members of the halogen family put on an act, you can be sure there will be something doing in the way of entertainment. The nimblest of the family quartet undoubtedly is chlorine. You have seen this actor in several roles before--bleaching dyes, and attacking metals with accompanying pyrotechnics, for example--if you have followed this series of articles. Iodine has made a personal appearance before you as a chemical detective, revealing latent fingerprints on paper. Another member of the family, fluorine, has shown you its remarkable power of etching glass when teamed with hydrogen. The remaining member of the quartet, bromine, is an irritating, rascally sort of character if encountered alone. However, when handcuffed to hydrogen, its behavior is so satisfactory that you should let it enter your home chemical laboratory and allow it to perform for you.

Uniting bromine with hydrogen yields hydrogen bromide, or hydrobromic acid--just as chlorine and hydrogen form hydrogen chloride, or hydrochloric acid. Hydrobromic acid reacts with substances to form bromides, as does its better-known relative, hydrochloric acid, to form chlorides.

Unlike most acids or acid-forming gases, however, hydrogen bromide cannot be prepared for practical purposes by heating corresponding salts with strong sulfuric acid. It is formed in the reaction, to be sure, but it is rapidly decomposed by the oxidizing action of the sulphuric acid. This difficulty is overcome by heating a bromide with strong phosphoric acid, which does not decompose the product.

To make hydrogen bromide, place a half ounce of potassium bromide or sodium bromide in an Erlenmeyer flask or a retort, with a capacity of sixty to 200 cubic centimeters (two to seven fluid ounces). Cover the chemical to a depth of an eighth of an inch or so with strong phosphoric acid, which you can buy at any drug store under the name of eighty-five-percent, or sirupy, phosphoric acid.

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