Qualitative Detection of Titanium Dioxide in Rubber

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Abstract
Titanium dioxide, either as such or in the form of the composite titanium whites, is now used to such an extent as a rubber pigment that a test for titanium is frequently necessary in the analysis of a compounded rubber. Owing to the insoluble nature of titanium dioxide, troublesome fusions are required to detect it by the normal qualitative tests in the ash remaining when a rubber is incinerated. The following method is offered as a quick and easy means of detecting titanium. A small portion (about 0.01 gram usually suffices) of the ash from the sample is placed in a clean glazed 15-cc. Porcelain crucible. One drop of concentrated sulfuric acid is then added, and the whole is heated on a hot plate for 30 seconds, i.e., until most of the acid is evaporated. The crucible is allowed to cool, and 2 drops of 6 N sulfuric acid added, followed by 1 drop of a 5 per cent aqueous solution of the sodium salt of chromotropic acid (1,8-dihydroxynaphthalene-3,6-disulfonic acid). A brownish red to purple coloration is obtained if titanium be present. In place of the chromotropic acid, 1 drop of 10-volume hydrogen peroxide is added in a second test, when the well-known golden yellow color is obtained.

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