Exercise 106. The Gel of Chromic Hydroxide

The following method was apparently devised by Reinitzer and was subsequently studied by Bunce and Finch. 

Twenty cubic centimeters of a 5 per cent solution of chromic chloride, to which 1 g. of sodium acetate had been added, is boiled in an Erlenmeyer flask provided with a funnel to serve as an air condenser. The boiling should be timed to 1 min. To one-half of the cooled solution, a solution of potassium hydroxide (1 3) is added until distinct alkalinity is reached. To the other half of the solution of chromic chloride ammonium hydroxide is added to alkalinity. 

Both of these alkalies give solutions which spontaneously form opaque gels, in appearance differing from each other in color only. The gel from potassium hydroxide is green, while that from ammonium hydroxide is bluish violet. 

Production of Gels by Reduction of the Salts of Metallo-acids. 

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