The entire subject is so recent, however, and astonishing developments have followed one another with such bewildering rapidity, that the aecom plishing of this purpose presented many difficulties. Almost every steel man knows the practical impossibility of obtaining detailed information concem ing tool steels which is absolutely accurate and reliable. The personal equation and a multitude of other factors commonly accounted negligible, so much affect results that the assertion might be safely hazarded that all conclusions as to method and means in steel treatment are subject to allowances for these elements. Thus, for illustration, two different plants operated by the some concern make large use of the barium process in hardening. At one the temperature commonly maintained and indicated by the pyrometer is 1200 degrees C. (2200 while at the other an instrument of the same make and calibrated with equal care uniformly indicates only 1070 degrees C. (1950 F.) and yet as far as can be seen by the eye of an experienced operator, familiar with both plants, the two baths are kept at identical temperatures. Certain it is that results equally good are obtained at both plants.