... 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 down thoroughly (0'0) with ice and salt; 10 cc. of concentrated sulfuric acid for each 100 cc. of solution ... — Organic Syntheses • James Bryant Conant
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