4 января, 2016 
Pokraskin A solution of 0.01 mole (1.44 grams) of /f-naphthol in 2 cc. 30 per cent sodium hydroxide is diluted to 400 cc., and 25 cc. 10 per cent soda ash is added. Ice-cold 0.1 N phenyldiazonium solution is added from a graduated cylinder or a cooled burette until a drop of the re-
action mixture on filter paper forms no more orange red dye with the diazo solution. Impurities may cause the formation of a colored streak after a few seconds, but this is always cloudy and is easily distinguished, with a little practice, from the pure naphthol dye. The number of cubic centimeters of the diazonium solution used gives the per cent purity of the /J-naphthol directly. A good product should be at least 99.5 per cent pure.
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