A normal solution of sodium hypochlorite is prepared as follows: in a 5-l. round-bottomed flask are placed 1800 g. of sodium hydroxide solution [300 g. (7.5 moles) of sodium hydroxide to 1500 g. of water] and 1500 g. of ice. Chlorine gas is then passed into the solution until it has gained in weight approximately 213 g. (3 moles). During this addition, the solution must be kept thoroughly cooled with ice, in order that chlorates will not be formed (Note 1). After all the chlorine has been passed in, it is necessary to be certain that the mixture is slightly alkaline, since any free chlorine in the solution prevents the formation of hydrazine.

In a 36-cm. evaporating dish are placed 1350 g. (1.5 l., 23 moles) of c.p. aqueous ammonia (sp. gr. 0.90), 900 cc. of distilled water (Note 2), 375 cc. of 10 per cent gelatine solution (Note 3), and 1200 cc. of the normal sodium hypochlorite solution prepared as above. This mixture is heated as rapidly as possible and boiled down until one-third of the original volume is left. This solution is then cooled thoroughly with ice and filtered with suction, first through two layers of toweling and then through one thickness of ordinary filter paper over cloth, in order to remove finely divided solid impurities. The solution is then placed in a precipitating jar, and cooled thoroughly (0°) with ice and salt; 10 cc. of concentrated sulfuric acid for each 100 cc. of solution is gradually added with constant stirring (Note 4). A precipitate of hydrazine sulfate (NH₂NH₂ · H₂SO₄) forms. The mixture is allowed to stand in the cold for a few hours in order to complete the precipitation, and is then filtered by suction in the usual way and the precipitate washed with cold alcohol. The yield varies from 53 g. to 58 g. per 1.5 l. of aqueous ammonia (34–37 per cent of the theoretical amount). The product is perfectly white and crystalline, and satisfactory for almost any purpose. If a very pure product is desired, it must be recrystallized from water. For every 21 g. of crude product, 100 g. of boiling water is used. If the crude hydrazine is brown, it is advisable to use a little animal charcoal. After the mixture has been filtered and cooled to 0°, 19 g. of pure white crystals are obtained (Note 5).