Abstract
Indium was discovered spectroscopically by Reich and Richter in Freiburg zincblende. Although widely distributed in minerals, it usually occurs only in very small quantities, and only recently Westbrook 1 worked out a process to isolate this element in larger quantities from crude zinc liquors which are residues from the manufacturing of sulphuric acid.
Indium is a white, lustrous metal, very soft and ductile and slightly heavier than zinc. It melts at 155° and boils at 1450°. It does not tarnish at ordinary temperature, but oxidizes rapidly above the melting point, burning with brilliant violet flame at higher temperature.
Chemically it resembles zinc in some respects and aluminum and iron in others. It is trivalent in stable compounds, and its sulphate forms alums with monovalent metal sulphates. Most indium salts are colorless, very soluble in water and hence do not crystallize easily. Alkalies precipitate the white indium hydroxide from the aqueous solutions of the salts, which precipitate may be redissolved by sodium and potassium hydroxide at room temperature, but it is reprecipitated at boiling temperature.
Preparation of Indium Solution. The material, for which we are indebted to the Grasselli Chemical Co., was stated to contain 268 gm. of indium chloride per liter. From this a tenth molar solution was prepared, containing 25.1 gm. of indium chloride per liter. This solution was found to have a pH of 1.8, using thymol blue as indicator. Attempts to neutralize this solution by means of alkali were not successful, because near the neutral point the hydroxide was precipitated. The mixture of indium chloride and sodium citrate, using 5 cc. M/10 indium chloride and 10 cc. M/10 sodium citrate can, however, be adjusted by means of alkali to pH 7.2 to 7.4.
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