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METALLURGY OF CAST IRON.
strength of test bars, every care should be taken to prevent one side being strained or pulled more than the other. The grip should be such as to cause an even pull all over the area of the specimen, in order to obtain the true tensile strength of the iron. See page 450. Another essential in operating testing machines is that of applying the weight as steadily as practicable. At Fig. 104 is shown the upper section of a type X of testing machine now being largely used, in which the oscillation of the beam F, from the lower stop H up to the upper stop K, in some cases may mean a load of 100 pounds, which if brought tip or down quickly results in a strain like an impact blow. A good plan to follow in using a machine of this design is to place one hand around the stop at K. By this plan, less room is allowed for the oscillation of the weighting
beam and the hand readily informs the mind of any upper movement, so that the sliding poise can be made to balance the beam before a bar could break to make it questionable within one hundred pounds of just what is its true strength, by reason of the beam F rising suddenly to the stop K.results. A comfortable speed, which can be always readily main tamed, should be adopted. In obtaining tensile