Summary 8 samples of tincture of digitalis have been compared chemically and biologically with a tincture prepared from the standard preparation of digitalis. The results of the frog assays do not agree with those of the chemical assays using the 3:5‐dinitrobenzoic acid reagent. A new method for the decolourisation of tinctures of digitalis has been investigated. The tincture is passed through an alumina column which adsorbs the pigments, and the eluate can be directly assayed with the Kedde reagent. The total time taken for decolourisation is at the most 5 minutes and the loss of colour‐producing active constituents—presumably due to adsorption on the alumina is less than 10 per cent. The constituents of 9 samples of tincture of digitalis have been identified by paper partition chromatography.

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