SPOT TEST FOR CHEMICAL RESISTANCE OF ENAMELED SURFACES*

A bstract A theoretical relationship between the color and thickness of thin films of amorphous silica was established. An acid‐resistance test based on this relationship was developed and applied in the testing of enamelware. According to the results obtained thus far, the color changes that are actually brought about by chemical attack agree with those which should occur theoretically. The test method thus appears to be fundamentally sound, at least insofar as this point is concerned. Its application in the testing of an enamel at different temperatures, as well as in the testing of various types of enamels at constant temperature, appears to afford satisfactory results. Enamel No. 41, when exposed for 48 hours to a solution of 20% hydrochloric acid at 60°F., developed according to this method of test a film about 675 a.u. thick. At 100°F. the film reached a thickness of about 2550 a.u. In the constant‐temperature tests the various types of enamels developed films in two hours that ranged from 60 to 2750 a.u. in thickness.