As stated before, at the top of each pot are several test pieces consisting of a whole scrap gear and several sections. After the pots have been heated at 1,600 deg.F. for about 5-1/4 hr., they are removed, and a scrap-section test-piece is quenched direct from the pot in mineral oil at _not more than_ 100 deg.F. The end of a tooth of this is then ground and etched to ascertain the depth of case. As these test pieces are of exactly the same cross-section as the gears themselves, the carburizing action is similar. When the depth of case has been found from the etched test pieces to be satisfactory, the pots are removed. The iron ball then is dropped into the tube to seal the hole in the bottom of the pot; the cover and the tube are removed, and the gears quenched direct from the pot in mineral oil, which is kept at a temperature not higher than 100 deg.F. THE EFFECT.--The heating at 1,600 deg.F. gives the first heat treatment which refines the core, which under the former high heat (1,700 deg.F.) was rendered coarsely crystalline. All the gears, including the scrap gears, are quenched direct from the pot in this manner. The gears then go to the reheating furnaces, situated in front of a battery of Gleason quenching machines. These furnaces accommodate from 12 to 16 crown gears. The carbon-steel gears are heated in a reducing atmosphere to about 1,425 deg.F. (depending on the carbon content) placed in the dies in the Gleason quenching machine, and quenched between dies in mineral oil at less than 100 deg.F. The test gear receives exactly the same treatment as the others and is then broken, giving a record of the condition of both case and core. AFFINITY OF NICKEL STEEL FOR CARBON.--The carbon- and nickel-steel gears are carburized separately owing to the difference in time necessary for their carburization. Practically all printed information on the subject is to the effect that nickel steel takes longer to carburize than plain carbon steel. This is directly opposed to the conditions found at this plant. For the same depth of case, other conditions being equal, a nickel-steel gear would require from 20 to 30 min. less than a low carbon-steel gear. From the quenching machines, the gears go to the sand-blasting machines, situated in the wing of the heat-treating building, where they are cleaned. From here they are taken to the testing department. The tests are simple and at the same time most thorough.