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• The results of the pre:lent investigation may be summarized as follows: (1) The heat content of carbon steels at high temperatures was determined by the mixture method, while the oxidation of the specimen was prevented by passing a purified hydrogen gas through the furnace. The specimens were twelve kinds of steels with different carbon contents from 0.09 % to 2.84 % and the range of temperature was 23~250°C. (2) According to A. Meuthen, the specific heat is constant below the A1 point, but the present writer showed that the specific heat is only constant above the A3 point, and that below this point, it increases with the rise of temperature. (3) The quantity of heat for the dissolution of pearlite in iron was determined by measuring the heat content above and below the A1 point. This heat increases proportionally with the content of carbon, reaches a maximum at 0.9 percent and ends at 6.7 percent. For the dissolution of I gr. of carbon in iron, a heat of 1760 calories is required, while, 16.1 calories are necessary for the dissolution of 1 gr. of pearlite in iron. (4) From the heat content-concentration curve, it was found that, the mean specific heat of cementite increases with the rise of temperature; it is 0.149 at 150°C and 02.20 at 850°C. (5) It was observed that the specific heat of the carbon poles with 98 %C increases almost linearly up to 700°C, and afterwards its rate of increase gradually diminishes. (6) It is confirmed by experiments that the A1 transformation is a function of temperature and time, but that the A2 transformation is a definite function of temperature only. (7) From the heat content-concentration curves, the heat of transformation from martensite to pearlite was obtained and found to be proportional to the carbon content. (8) The heat of transformation from austenite to martensite, or that from martensite to pearlite, increases proportionally with the content of eutectoid carbon. The heat of transformation from austenite to martensite for a eutectoid steel amOlmts to 5.9 calories.