438 METALLURGY OF CAST IRON.
There have been several other machines designed for
testing hardness sinc.e Professor Turner perfected his machine. One is a design by Mr. W. J. Keep, being an improvement on one designed by the late Mr. C. A. Bauer, M. E., and which was presented at the New York meeting of the American Society of Mechanical Engineers, December, 1900, and also described in the American Machinist, February 28, 1901. Fig. 53 shows an ordinary drill press which was fitted up by the author to test the hardness of metals, and which worked very satisfactorily for the class of testing it was intended for. A full description of this machine is given on pages 234 and 238.ssor Turner clearly presents the utility of his device and illustrates the thorough manner in which he completed his work. It has been thought by some inexperienced founders that there is no limit to silicon softening* iron, but this is strongly refuted by the following Table 87 and sustains the author in statements made in other writings to the effect that silicon can harden as well as soften iron: