434 METALLURGY OF CAST IRON.
In reference to testing chilled iron, Mr. Isa W. Whitney, in a paper on " Chilled Iron," before the Philadelphia Foundrymen's Association, January 6, 1897, showed that the transverse strength, as well as the resilience of chilled iron, is the greatest in the direction of the chill crystals. He also shows that " tumbling " chilled or white iron is not as effective in increasing the strength of iron as is the case with medium or gray irons, qualities cited on pages 441 and 442.
Reliable methods for testing hardness of iron have long been needed. It is often as important to test the degree or character of hardness in castings as any other physical properties. There are quite a number of manufacturing industries of the character like chill roll founders, car wheel works, crushing machinery, die and brake shoe manufacturers, that could, had they but a good reliable hardness test, find it in time to be as important, if not often more so, than any tensile or transverse tests they could use. We have no physical test that has proven more unsatisfactory than that of obtaining the hardness of iron. However, improvements are being made as shown on pages 435 to 438 that may meet many requirements. Many plans have been used to ascertain the relative hardness of material. One, which was popular for a time, is said to have been proposed by Moh, and is classed under three heads: (i) Any material which could be scratched by a finger nail, (2) that scratched by a knife blade, (3) and that affected by a file. After the above came the weighted diamond point, followed by the punch struck with a given weight. The diamond point device was used by means of weights sliding on a lever, and as the specimen to be tested was moved the weighted diamond would trace a scratch or leave a cut the character of which recorded the hard-ther on.cibly illustrates the great reason why the founder has to fear sulphur in fuel, high-sulphur iron, and to j