452 PRACTICAL ORGANIC CHEMISTRY the condensers is desirable however, both for training in sound analytical practice, and also to protect the contents of the flask from condensed steam, etc. 2. DETERMINATION OF THE NUMBER OF HYDROXYL GROUPS IN (ii) GLYCOL. C 2 H 4 (OH) 2 . Molecular Weight, 62. Carry out the determination precisely as for phenol, but add about 0-5 ml. (approximately 0-5 g.) of glycol to the flask A, and weigh as before by difference. (iii) GLYCEROL. C 3 H 5 (OH) 3 . Molecular Weight, 92. Use approximately 0*5 ml. of glycerol, and cork the flask A securely when weighing the glycerol by difference, owing to the very hygroscopic nature of the latter. Heat on the water-bath for 6o minutes instead of 30 minutes. Excellent results are obtained by this method if a freshly opened sample of anhydrous glycerol is available: a sample which has been exposed to the air for even a short period will absorb sufficient water to give inaccurate results. (iv) MANNITOL. C
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