Three hundred grams of β-naphthol (2.1 moles) is converted into nitroso-β-naphthol (Org. Syn. Coll. Vol. I, 1941, 411) (Note 1), and the product is transferred to a 6-l. (1.5 gal.) crock which is wide enough to admit the Büchner funnel (30-cm.) employed. A cold solution of 600 g. (5.8 moles) of sodium bisulfite and 100 cc. of 6 N sodium hydroxide solution in 2 l. of water (Note 2) is used to rinse the material adhering to the funnel into the crock. The mixture is diluted with water to 4–4.5 l. and stirred until solution of the nitroso-β-naphthol is complete (about fifteen minutes). The dark solution is siphoned onto a large Büchner funnel and filtered by suction, thus removing a small amount of tarry material which is always present. The clear, yellowish brown filtrate is transferred to an 8- to 10-l. wide-mouthed bottle and diluted with water to 7 l. While the solution is vigorously stirred, 400 cc. of concentrated sulfuric acid is poured slowly down the walls of the bottle; the mixture is then placed in the hood and protected from the light (Note 3). The temperature rises from 20–25° to 35–40° at once and to about 50° in the course of two hours, when the reaction is nearly complete. After standing for a total of five hours or more (Note 4), the precipitate, which sets to a stiff paste in the bottle, is collected on a filter. The residue is transferred to a 1-l. beaker and washed with 200 cc. of water. The mixture is filtered, and the residue is washed with 300 cc. of water on the filter. The moist material weighs 700–800 g. No appreciable decomposition takes place on drying the product to constant weight at 120°. A light powder of fine, gray needles is thus obtained. The yield is 410–420 g. (82–84 per cent of the theoretical amount based on the β-naphthol used) (Note 5).