CHAPTER LXIX. UTILITY OF THE TEST BAR AND STAND-ARD SYSTEMS FOR COMPARATIVE TESTS.* Many lose sight of the real utility of test bars. They entertain the idea that they will give the actual strength, contraction or chill of single or tmduplicated castings. The only way to obtain positive knowledge of these qualities is by making test bars of the same thickness and form, if possible, as those of the casting for which comparisons were to be drawn. In reality this would mean making two castings to he poured at the same time with the same iron, and breaking one to get the strength, etc., of the other. The true utility of the test bar is simply comparative, to define differences that may exist in mixtures of the various 'c grades '' of iron, or, in other words, all that the test bar will do is to denote the strength, etc., of the iron which is poured into the mould; and what the shape and size of that mould would do to distort the physical qualities of the iron from agreeing with what the test bars have recorded, is largely left for experience to guess at or comparative tests of broken castings to define. * Revised paper presented by the author to the Foundrymen's Association, Philadelphia, Pa., December 2, 1896. pages 509 and 514.