Discussion on “an overpotential test for insulators”

C. E. Skinner: Porcelain is essentially in effect a conglomerate of spar, flint and kaolin. Each individual piece has its own personal history. A very large number of factors inevitably enter in, to affect it for good or ill in its making. Much can be done by the ceramist and by the porcelain factory to insure uniformity, but the day will never dawn when lots of porcelain insulators can be tested by sample as we test steel and many other materials. We must always test each piece to see that that piece does not have accidental defects and weaknesses that would unfit it for its intended service. What is required is a test that will search out such defects and weaknesses and which will leave the piece uninjured by the test itself. It is up to the porcelain manufacturer to so operate his plant that he secures the maximum of uniformity, and the test should eliminate all pieces which fall below an agreed standard. The agreed standard should be that which gives satisfactory service under the prescribed conditions. As no test can duplicate service conditions — in fact probably no series of tests can duplicate service conditions — the combined experience of manufacturing, testing and service will finally show what balance should be struck between severity of test and service. We can so test that we destroy every insulator, then we have none for service. The most careful manufacturer cannot hope to so fabricate that no test is required, so there must be an economic balance between test and service. We all welcome any test that will help to show us whether design and material are right, and any test that will eliminate insulators which would not give service.