In order to obtain the maximum yield, it is necessary to cool the hydrochloric acid solution of the phenylhydrazine hydrochloride from 20'0 to 0'0, before filtration. From 5 to 10 per cent of product separates between these two temperatures. When this is done, no more phenylhydrazine hydrochloride is obtained by concentration of the mother liquor. An increase in the amount of hydrochloric acid above 2 l. for the precipitation of the hydrochloride produces no increase in yield of product. Most published directions for the preparation of phenylhydrazine specify the use of zinc dust and acetic acid following the reduction with sodium sulfite. No improvement in the quality or quantity of the product was obtained by using zinc and acetic acid. It is best to use freshly prepared sodium sulfite for the reduction, since the commercial quality is poor and gives a lower yield of phenylhydrazine. A cylinder of liquid sulfur dioxide should, of course, be available. The rapid addition of the diazonium salt solution to the sodium sulfite seems to be advantageous. Pure phenylhydrazine dissolves in dilute acetic acid to yield a perfectly clear solution. The phenylhydrazine hydrochloride may be purified by crystallizing from water. A 600-cc. portion of water is used for 100 g. of crude hydrochloride, and the solution boiled a short time with a few grams of animal charcoal. After filtering, 200 cc. of concentrated hydrochloric acid are added, and the mixture cooled to 0'0. Pure white crystals in a yield of 85-90 g. are obtained. Rubber gloves should be worn when working with large quantities of phenylhydrazine, since the product may cause serious injury to the skin. The vapors of phenylhydrazine should not be inhaled. 3. Other Methods of Preparation Phenylhydrazine has been prepared by the reduction of benzene diazonium salts with sulfites;[1] by the reduction of benzene diazonium chloride with stannous chloride;[2] by the reduction of benzene diazonium hydrate with zinc or sulfur dioxide;[3] by the reduction of sodium benzene diazotate with sodium stannite;[4] by the reduction of diazoamino benzene;[5] by the reduction of nitrosophenyl hydroxylamine or its methyl ether;[6] and by the action of hydrazine hydrate on phenol.[7] [1] Ann. 190, 79 (3878); Ber. 20, 2463, (1887). [2] Ber. 16, 2976 (1883); 17, 572, footnote (1884). [3] Ber. 31, 346 (1898). [4] Ber. 36, 816 (1903). [5] Ber. 31, 582 (1898). [6] Ann. 190, 77 (1878). [7] Ber. 31, 2910 (1898). The most feasible method consists in the reduction of diazonium salts with sodium sulfite. Although this method is given in several laboratory manuals, the results were not found entirely satisfactory. The present directions provide for a lengthy but essential heating of the diazonium-sulfite mixture, omit the useless zinc dust reduction, and supply exact details for preparation on a fairly large laboratory scale. XX