:H h * 1 224 APPENDIX VII p 11 the furnace temperatures and, due to the heat-storage capacity of the brick, a smoother curve is obtained. The temperature gradient between the two curves includes the resistance of 1 in FIG. 155.—Curves Showing the Temperature Changes in the Hot Gases Cooling, the Cool Gases Heating and the Checker Brick. These curves showing these temperature changes during the normal or ideal period or cycle are indicated by the legends. The abnormal cycle or the changes due to overheating and overcooling are marked with reference letters. The latter condition is the one that occurs when a cold checker is heated in starting. Ag cooling curve of hot gases passing through a cold checker; JBff cooling curve of hot gases passing through a checker with too long a heating period; Off cooling curve of hot gases passing through a checker after it has absorbed its maximum amount of heat; Aa heating curve of cold gases passing through an overheated checker; Ba, heating curve of cold gases passing through a checker with too long a cooling period; Co, cold gases passing through a cold checker; Db cold checker prior to heating; Eb checker initial heating curve. The upper portion after becoming heated trans-1 mits heat to lower portion by conduction; Fb checker overheated in upper portion. Heat is transmitted by conduction to raise temperature of lower portion; Hb overheated checker prior to cooling. of brick as well as any surface resistance which may exist, and this difference rarely exceeds 150°. This would seem to indicate that a heat differential of less than 300° might be obtainable under good working conditions from gas to gas.