Note 686 — PHARMACOLOGIA. (continued 7)

The change of colour which Guaiacum undergoes by admixture with other bodies, not only affords a test by which we may appreciate its purity, but at the same time it becomes a reagent by which we may assay the virtues of other vegetable substances. According to the experiments of M. Taddey and Rudolphi, it appears that Guaiacum in powder, is an excellent test for vegetable gluten, forming with it a fine blue colour, whence it affords the means of determining the quality of wheat flour. From the experiments of M. Planche, it moreover appears that there is a series of vegetable roots which, when fresh, are capable of producing a blue colour, if introduced into an alcoholic solution of Guaiacum: so that we may hereafter be furnished with a chemical test that will at once appreciate their freshness, which is undoubtedly one of the greatest desiderata of pharmaceutical science.

A communication has appeared from Mr. A. T. Thomson, in which he proposes Guaiacum as a test for the freshness of Colchicum. I have, however, never been able to succeed with it, to my satisfaction.