Asbestos-sodium silicate stoppers

Corks are badly attacked and must be renewed in each run. It is preferable to employ asbestos - sodium silicate stoppers, which can be used repeatedly. 

Old rubber stoppers may be used, but are slifthtly attacked. Asbestos-sodium silicate Stoppers (for preparation, see Section III,161,Note 2) or ground glass joints are, of course, to be preferred. 

Arsenic, detection of, 1043 Aryloxyacetic acids, 682 Asbestos-sodium silicate stoppers, 494 Aspirin, 996... 

The yield is reported to be improved by the following modification of the method described. In a 3-I. three-necked flask provided with a stirrer, reflux condenser, and dropping fuimel, set in asbestos-sodium silicate stoppers (5, 9), are placed 1900 cc. of 50 per cent nitric acid (1262 cc. of nitric acid, sp. gr. 1.42, diluted to 1900 cc.) and i g. of ammonium vanadate. The flask is surrounded by a water bath heated to 50-60°, and, while the mixture is stirred, 357 g. (3.5 moles) of commercial cyclohexanol is added very slowly so that the temperature of the bath is maintained at 50-60°. This requires about six to eight hours. The reaction is completed by heating the water bath to boiling until the evolution of nitrogen oxides has ceased (about one hour). The hot reaction mixture is siphoned off and allowed to cool. The yield of crude adipic acid is 372 g. (72 per cent of the theoretical amount). 

The transfer to the retort must be made before the mixture solidifies. The best method of closing the tubulure of the retort (unless this consists of Pyrex glass) is by means of a glass stopper too small for the hole and wrapped with asbestos paper moistened with sodium silicate solution. 

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