Rubber stoppers washing

Mix 50 ml. of formalin, containing about 37 per cent, of formaldehyde, with 40 ml. of concentrated ammonia solution (sp. gr. 0- 88) in a 200 ml. round-bottomed flask. Insert a two-holed cork or rubber stopper carrying a capillary tube drawn out at the lower end (as for vacuum distillation) and reaching almost to the bottom of the flask, and also a short outlet tube connected through a filter flask to a water pump. Evaporate the contents of the flask as far as possible on a water bath under reduced pressure. Add a further 40 ml. of concentrated ammonia solution and repeat the evaporation. Attach a reflux condenser to the flask, add sufficient absolute ethyl alcohol (about 100 ml.) in small portions to dissolve most of the residue, heat under reflux for a few minutes and filter the hot alcoholic extract, preferably through a hot water fuimel (all flames in the vicinity must be extinguished). When cold, filter the hexamine, wash it with a little absolute alcohol, and dry in the air. The yield is 10 g. Treat the filtrate with an equal volume of dry ether and cool in ice. A fiulher 2 g. of hexamine is obtained. 

In each of two ordinary 250-cc. (8-oz.) narrow-mouthed bottles are placed 32.1 g. (32.5 cc., 0.3 mole) of m-toluidine and 33 (23 cc-y °-3 mole) of ethyl bromide (Note 1). The bottles are sealed with rubber stoppers wired tightly in place and then allowed to stand for twenty-four hours in a 2-1. beaker filled with water at room temperature (Note 2). The white crystalline mass in each bottle is broken up and the amine is liberated by shaking with 150 cc. of 10 per cent sodium hydroxide solution and 50 cc. of ether. The contents of the two flasks are combined, the lower aqueous layer is separated and discarded, and the ether solution of the amine is washed with 150 cc. of water, When the ether is distilled from a steam bath, the crude amine (90-92 g.) is obtained. 

Transfer the silver halide precipitate to the filter by means of a delivery tube (Fig. 41), previously carefully cleaned. Attach the delivery tube to the filter tube by means of a small rubber stopper. Lower the delivery tube to the bottom of the beaker and draw over the precipitate at a moderate speed (about two drops per second). Then wash with a little alcohol and, when the alcohol has been drawn through, with a little dilute nitric acid (1 100). If necessary repeat the successive washing with a little alcohol and a little water. Finally wash with alcohol the end of the delivery tube which is in the filter tube, fill the cup of the filter... 

Rubber stoppers should be used throughout, including the drying of reagents, as corks contain some moisture. The stoppers should be boiled in 10 per cent sodium hydroxide solution for two hours, thoroughly washed with dilute acetic acid, and dried. 

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