The sodium sulfite solution is placed in a 12-l. flask and cooled to about 5'0. Approximately 500 g. of cracked ice are added, and then, with mechanical stirring, the diazonium salt solution is run in as rapidly as possible. The mixture becomes a bright orange-red. The flask is now warmed to about 20'0 on a steam bath, until the solid sodium sulfite, which has separated while cooling, redissolves. The total amount of liquid is now about 10 l. One-half of this is poured into another 12-l. flask, and both halves are warmed on the steam bath to 60-70'0, until the color becomes quite dark (thirty to sixty minutes). Sufficient hydrochloric acid (300-400 cc.) is now added to each flask to make the solutions acid to litmus. The heating is continued and the color gradually becomes lighter until, after four to six hours, the solutions have become nearly colorless; they may be heated overnight, if desired. To the hot solutions are now added about one-third of their volume of concentrated hydrochloric acid (2 l. to each portion) and the mixtures cooled, first in running water, then in a freezing mixture, to 0'0. The phenylhydrazine hydrochloride precipitates in the form of slightly yellowish or pinkish crystals which may be filtered off and dried. The free base is liberated by adding to the phenylhydrazine hydrochloride 1 l. of a 25 per cent solution of sodium hydroxide. The phenylhydrazine separates and is taken up with benzene (two 300-cc. portions). The combined extractions are well dried with 200 g. of solid sodium hydroxide, poured off, and distilled. Most of the benzene may be distilled under ordinary pressure, and the remainder, and any low-boiling impurities, under diminished pressure. The pure phenylhydrazine boils at 137-138'0/18 mm., and is obtained as a pale-yellow liquid. It can be crystallized on cooling in an ice bath; the crystals melt at 230. The crude phenylhydrazine from two lots of aniline (744 g.) is best distilled at one time and gives 695-725 g. of pure product (80-84 per cent of the theoretical amount). 2. Notes If the sodium sulfite solution contains an excess of alkali, a black tar tends to form when the solution is warmed, and very little phenylhydrazine is obtained. Great care must be taken in determining the end point in the neutralization of the sodium hydroxide by the sulfur dioxide. If the sodium sulfite-diazonium salt mixture is acidified before warming or before becoming dark, the red color of the solution does not disappear on heating, and the precipitated phenylhydrazine hydrochloride obtained is colored red. The benzene solution of phenylhydrazine should be well dried before distilling, since the presence of moisture causes an increased amount of foaming to take place just after the benzene has distilled off. When the distillation is carried out carefully, practically no phenylhydrazine distils with the benzene or other low-boiling impurities.