The Weber Color Test for the Identification of Natural Rubber

Abstract

Abstract The Weber color reaction, mentioned in a recent note, has become of importance in detecting natural rubber in mixtures in which it may be considerably diluted with synthetic rubber or nonrubber materials. The detailed instructions for carrying out the test are given elsewhere, and Stern has published a table which shows also the colors obtained when the test is applied to rubbers other than the natural product. It is clear from this table, and is confirmed by our experience, that the strong violet color developed is distinctive for natural rubber and gutta-percha, provided that the material has been extracted with acetone. However, color reactions in organic chemistry are rarely found to be as specific as earlier workers have claimed, and work is being carried out in these laboratories to establish the limitations of the reaction when applied to rubberlike materials. With very few exceptions, synthetic rubbers and rubberlike materials available at present do not give a positive result with this test, although very faint violet colors, which cannot be confused with a positive result, are sometimes obtained. Those giving any violet color are listed in Table I.