Results The spectrum of aloe-emodin in 0.1 M boraxsodium carbonate buffer of pH 11 is given in Fig. 1. The spectra in the buffers of other pH values were almost identical with the spectrum given. Beer's law was followed in all cases in the region from 450 to 510 millimicrons with concentrations up to 0.04 mg. per ml. where the measurements become uncertain.
