Clark''s 0.2 M boric acid solution, made 0.2 M with respect to KC1, also was used with''0.2 M Na2CO3. The range for 95 of the former to 5 of the latter, and with the proportions reversed, is pH 7.44-10.85 at 16[degree]C. Phenolphthalein may be used up to pH 10.5 and Soren-sen''s alizarin yellow R, sold as alizarin yellow G or p-nitrobenzene-azo-salicylic acid, from pH 10.1 to beyond the range of the mixtures given.