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The American Carbon Manual/A Hint on the Preparation of Solution of India-rubber in Benzole

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A scientific friend has directed our attention to a curious circumstance which he has observed in preparing a solution of India-rubber in benzole; and, as many of our readers have met with difficulties in the direction which we shall now mention, we throw out the hint here. Our friend had great difficulty in preparing a solution of the gum even moderately clear, and, as he wished to have some perfectly bright for particular work, he made many experiments upon the subject. On thinking over the matter, he came to the conclusion that it is the moisture of the India-rubber which communicates the milky appearance to the benzole solution. On boiling the liquid for a minute or less, all this moisture was found to be given off in addition to a little benzole, and, on cooling, the liquid remained perfectly clear, although rather thickened. The addition of a very small quantity of water caused the resumption of the original opalescent appearance, thus proving clearly the cause of the peculiar properties of the solution.

On repeating this experiment before us, we suggested to our friend that the addition of any very hygroscopic substance which would remove the water from the liquid should produce the same result as boiling, and in a very much more simple way. A few fragments of fused chloride of calcium were, therefore, added to some of the opalescent liquid, and with the result of rendering the liquid perfectly clear after a few minutes' standing upon the salt. The chloride of calcium can then be removed, as it is quite insoluble in the benzole, and the liquid then preserved for use.

There is another fact in connection with this subject which it may be interesting to mention. When a dark-colored sample of India-rubber is used in preparing the benzole solution, the brown color may be almost completely removed by the addition of a little water to the liquid. An emulsion is then formed of a milky appearance, and which leaves, on evaporation, a film but slightly colored.—Br. Jour.