They are rather delicate articles to make except for immediate use as the thin material is liable to become over vulcanized.
In the chemical laboratory sheet rubber can be used for covering the ends of glass stirring rods. These answer very nicely for cleaning out from beakers the last particles of a precipitate. The sheet is cut of proper size and is bent around the end of the rod and cut off close with a pair of scissors. It adheres where cut. It is then pinched with the fingers to bring the edges into better contact and the operation is complete. A slight heat makes it adhere better.
To connect glass tubes in setting up laboratory apparatus the same material was formerly used. It was wrapped around the joint, tied with thread and slightly warmed. At present this form of connection is wholly displaced by ready made rubber tubing.
It is interesting to observe in all articles made from this sheet the marks of the original cutting knife. These may be observed in inflated balloons, as parallel lines running all over the surface, and magnified by the expansion due to the inflation.
CHAPTER XI.
VARIOUS VULCANIZING AND CURING METHODS.
The regular methods of vulcanizing and curing can be departed from and good results obtained. A few excellent methods differing essentially from the ordinary ones are described which will be of service to workers on the small scale, as they enable one to dispense with vulcanizer and air bath entirely.
One type of curing process does away with the air or steam vulcanizer, and substitutes, as the curing agency, a hot bath of liquid. For this purpose a fluid is required that will not act injuriously upon the india rubber, and which will give a curing temperature without boiling away. One favorite liquid is glycerine. This can be heated to the necessary degree and is an excellent substitute for the expensive apparatus often used. For experimental work it is exceedingly convenient.
In use it is placed in a vessel of proper size and a thermometer is suspended so that its bulb dips into the liquid near one side and does not touch the bottom of the vessel. The heat is applied by a gas burner, alcohol lamp or oil stove. Of course the vessel may be placed on an ordinary cooking stove or range, and the heat may be graduated and adjusted by moving it about until it reaches a part of the stove where the proper heat will be maintained.
The mould with its contents is immersed in the glycerine, care being taken to see that it so placed as to assume the mean temperature of the liquid and not to be heated too hot. This might happen if it stood on the bottom of the vessel, so it is well to have it supported or suspended a little above it.