176 METALLURGY OF CAST IRON.
tested for hardness they would be found so different that anyone, guided by hardness tests, would say that No. i would make a very soft casting while No. 2 would make a very hard one, when in fact each will give like softness in like castings and treatment in cooling. These samples were drilled with a press running at uniform speed and pressure. It took eight ^ minutes to drill No. i and twenty-two minutes to drill" No. 2, a difference of fourteen minutes. A half-inch twist drill was used and the method of drilling will be seen by the half holes on the back of the specimen seen in No. 3. The difference in the hardness of these samples, it is to be remembered, is found in samples of like analysis, excepting in combined carbon and in iron, coming from the same tap and cast in sand moulds. • As long as uniformity in making iron cannot be achieved, as is illustrated in Chapter XXIV., we may expect that the state of the carbon or hardness of pig iron will vary, and often not be in accordance with the grade results as shown by the percentages of silicon, sulphur, manganese, and phosphorus which will be in the pig iron. It will appear ridiculous to I those who know, by experience and research, the [ deceptive nature of the appearance and hardness of J sand-cast pigs that any one should now, at this day of / advancement in the metallurgy of cast iron, try to | introduce a. hardness test to define the grade of pig | iron as now being generally cast. j! It is not to be understood that every cast of pig '! metal is deceptive to the eye, or hardness test. It may >-V be that three-fourths of all the iron cast at some furnaces may possess a true fracture of hardness or accord with the amount of silicon, sulphur, etc., an "