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Simple tests, as developed for daily production of electrical porcelain are given.Laboratory tests are described and results for a number of ceramic insulating materials are given. From these it is shown that mechanical strength and resistance to thermal shock are valuable indications of the mechanical properties of bodies and glazes. Results obtained in testing foreign-and American-made porcelains are compared.

or devise more selective methods to take care of new combinations such as were needed when glasses containing fluorine and boron became common.