()PIiRATIN(r TESTING MACHINES.
Obtaining true results or close records in testing is often assisted as much bv careful work and system in operating testing machines as by correct methods in the moulding, casting, etc., of test bars.
In obtaining the transverse strength and deflection of bars cast flat they should always be laid on the bearing blocks the same way. The importance of this is realized when we consider that the down or *l nowel " side of a one-inch area round or square bar can be made to show a strength of 300 to 400 pounds more by having the v" nowel " side resting on the blocks than where the cope side is so placed, a quality clearly proven in Chapter LXY., pao-e 4<SS.
If bars are cast on end, it is well to have the down or upper cast end always pointed the same direction.* To insure this in the methods advocated by this work, a small, flat depression is cast in the bars, so as to permit. their always finding a i^'ood bearing at the same spot of the bars, as seen at X, Piij;'. 103,next paj^e.
The same speed in testing should always be maintained as far as possible, as whether a bar is broken fast or slowly can make a difference in results. A comfortable speed, which can be always readily main tamed, should be adopted. In obtaining tensile
*This is essential, as it assists in obtaining an approximate area at the. breaking point, as the taper of the patterns and straining of the mould from head pressure are liable to make the area of the bars vary at different heights.on produced.