ethanol containing hydrogen chloride, dissolving the separated hydrochloride (m. p. 163-165°) in warm 95% ethanol and pouring the solution slowly into cold water, yielded the pure base of m. p. 72-73°.Ultraviolet Spectra.-The apparatus used was a Beckman Model DU Quartz Spectrophotometer. The solvents were:for I, 95% ethanol; for II purified dioxane" finally redistilled through a 15-ball Snyder column with rejection of the fore-run; for III, pyridine dried over solid potassium hydroxide and distilled, only the middle fraction being used. The samples were purified as follows.Compound I was obtained from the hydrochloride (crystallized from 1 N hydrochloric acid) by action of warm aqueous ammonium hydroxide, and was then crystallized from 50% ethanol. Compound II was obtained pure from I by twice crystallizing from anhydrous dioxane. Compound III was obtained from I by two crystallizations from pyridine, and was freed of adhering solvent as described above. The ultraviolet spectra are shown in Fig. 1.Infrared Spectra.-Samples of I, II and III, purified as outlined, were suspended in "Nujol" and examined in a double-beam infrared spectrophotometer. 23 The plotted results appear in Figs. 2 and 3. Molecular Weight Determinations.-The Cottrell ebulliometer,24 enclosed to exclude drafts, was swept out with dry nitrogen before each determination. About 65 ml. of solvent (dried and fractionally distilled) was used, and in each case several values were obtained at increasing concentrations. At higher concentrations some difficulty was encountered owing to irregular splashing and foaming. The results, calculated in terms of extents of association, are shown graphically in Fig. 4. (22) Fieser, "Experiments in Organic Chemistry," D. C. Heath and Co., N. Y., 2nd ed" 1941, p. 369.(23) The spectra were determined by Samuel Sadtler and Son, Analytic and Consulting Chemists, Philadelphia, using an instrument made by Baird Associates, Inc.(24) The low solubilities of the compounds in permissible solvents near their freezing points made the freezing point method inapplicable.

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The preceding paper of this series3 showed that the imide hydrogens of certain dipyrrylmethanes do not react with molten sodium and potassium.Conceivably, these peculiarities could be due to

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