THE USE OF CORKS AND RUBBER STOPPERS

Although these have been largely replaced by ground glass joints, corks and rubber stoppers still find occasional use in the laboratory. 

Two points must be borne in mind when selecting a cork stopper. In the first place, the cork should be examined for flaws unless corks of the highest quality are employed, they are liable to have deep holes, which render them useless. In the second place the cork should fit into the socket to only about one-quarter of its length. It should then be softened by rolling in a cork press or by wrapping it in paper and rolling under the foot. 

To bore a rubber stopper, it is essential to employ a very sharp cork borer of the same size as the tube to be inserted into the hole. The borer is lubricated with a little glycerol or alcohol and steadily rotated under only very slight pressure. The operation requires a good deal of patience and time and frequent lubrication may be necessary if too much pressure is exerted on the borer, a hole of irregular shape and diminishing size will result. 

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