VALUE OF MICROMETER MEASURE-MENTS IN TESTING.
««What is worth doing at all, is worth doing well,59
is an old maxim, and never more applicable than to the subject of testing. It can be readily observed that the author is an advocate of utilizing every factor that can, in any manner, assist in lessening erratic records and advance testing of cast iron to its highest perfection. Such advocacy would be inadequate did the author not argue for the adoption of the micrometer to measure the area of test bars at the point of fracture. The micrometer would be used much more than it is at the present time, did testers only more fully realize the difference a few thousandths of an inch in the diameter of a bar can make in the strength records, especially when the same are reduced to make relative comparison of strengths.
Many would be surprised to learn how often they have been deceived in according differences in strength to records obtained simply by calipers and common rule in considering the size of bars for comparisons. If the micrometer had been used and the area reduced to make relative comparisons as illustrated on page 475, testers would ofttimes have found bars, which were conceded by the breaking load records to be the "frongest, to prove the weakest test of iron,'igures 1.596 or 1.955, as the case may be, replace the 1.128, which is the diameter of a bar equal to the area of a one-inch square bar. It may be well to mention at this point that the Riehle Bros, of Philadelphia and others now use the method for computing the strength of test bars shown in Table 99, page 476. 1.006 — 3,686 Ibs. strength per sq. in.