DURING the past few years the questions of rock drills, drill bits and drill steel have received much attention, and many improvements have been brought about, both in the design and in the use of rock drills and drilling equipment. Among these improvements the use of smaller changes in gage between the different steels has been one of the most important. With the old types of piston drill, gage changes of ~ inch or more were often used, necessitating the use of steel Of from 3 to 3~ inches in

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... iameter to start when deep holes were to be drilled. As the work of drilling varies almost directly with the quantity of material removed, the use of these large sizes of steel resulted in a great loss of time and energy. At the present time, many companies are successfully using gage changes of 1/1 ~ inch, and in some cases changes of only 1/3 ~ inch are used. Although these very small changes require great care and accuracy on the part of the drill sharpener, both in forging and gaging the steels and in proper heat treatment, still the cost of this extra work in the drill shop is more than offset by the increased efficiency of the drilling machines. Another improvement in drilling practice that has been brought about recently by several companies is the use of I-inch steel in place of I ~ inch in the large mounted hammer drills. The advantage of the smaller cross-section consists in the saving in steel, faster drilling speed, and saving in labor on the part of the miner in handling the lighter steel. In order to lind out whether or not these improvements were applicable in the Missouri-Kansas-Oklahoma districts, the Mississippi Valley experiment station of the Bureau of Mines, work-