For material of the specimens, machinery cast iron of ordinary graphitic structure is used, and for measurements of their elasticities, a newly designed extensometer, which the author believes is better suited than any one else to the present investigation, is employed. By the use of this apparatus, not a few phenomena which have hitherto been overlooked, were noticed in the atmospheric temperature study. Thus, notwithstanding the first idea of the investigation was toward elevated temperatures, this is discussed in detail, such as, (1)phenomena of castingstress inducement are noticeable even in a most carefully prepared specimen; (2)Hysteresis loop of cast iron enlarges its area according to the augmentation of the maximum load; (3)In a hysteresis curve, the line of unloading is almost a straight line from the second step of reversing to no load; (4)The area of a hysteresis loop is the largest at the first test, the repetition within the same limit of loading makes it smaller and smaller until it reaches some constant, generally three or four repctitions being sufficient for the arrival at this constancy; (5)In cast iron there exists something like a yield point of ductil metal, and in the present investigation it lies somewhere between 770kg and 900kg per sq.cm.; (6)If so called yield point has been once reached, hereafter for any higher load, a similar phenomenon always occurs, i.e., when loaded, extension increases with lapse of time, always requiring several minutes to settle. Regarding investigation at elevated temperatures, the test at ordinary temperature was invariably made for each specimen beforehand, so that reasonable study on temperature effects might be performed, regardless dissimilar properties of cast iron. Tested temperatures were from 100℃. to 700℃. at the step of 100℃. Up to 500℃. heating, no remarkable alteration was noticed upon the elastic properties, except some increase of strain against each corresponding load and also some increase of permanent set, all of which become a little greater with temperature rise. By the heat of 600℃. cast iron loses elasticity a great deal, therefore considerably improving its plasticity, yield point appearing at the stress less than 350kg/cm^2,and over 701kg/cm^2 stress, extension being so great that the reading scales were out of sight. At 700℃., the above qualities appear in more intensified manner, such as, at the stress less than 175kg/cm^2,already displaying yield point, and thus showing it has become very plastic. Elastic constants at ordinary and elevated temperatures are calculated from the results of each test.

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In the evaporation test of steam boilers, the quantity of heat absorbed by the furnace wall during the heating period will be very large compared with that after the thermal stationary state is arrived at. The author proposes to establish some rule on the preliminary firing period for such cases to limit the error of result within a certain range, and formulae to calculate it are given with an example.

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The growth of crystal grains in metals caused by annealing and the influence of the crystal size upon their mechanical properties have been studied by several investigators. Recently experiments have also been carried out for finding some relation between the grain-size and mechanical properties. According to Stead, the mechanical disease is not due to any change in the crystals themselves, but is due to the intercrystalline weakness. There are, however, another type of weakness, so called the intracrystalline one. According to the first hypothesis, the greater is the number of grain, the stronger should be the resistance to the external force, H.T. Angus has experimentally found an empirical formula concerning with the hardness H and the number of grains n in the case of copper, that-is, a law "H is proportional to √<n>." But according to the second hypothesis, the result should be contrary. In the case of steel, there has, however, been found, up to the present, no definite relation : between the grain-size and the mechanical properties, except a qualitative relation that the decrease in grain-size is accompanied by an increase in the hardness and an improvement in the tensile properties. The properties of steel varies considerably with a slight changes in the carbon content and also with heat treatments. The grain-growth in steel is complicated by virtue of the existence of transformation. In my experiment, after necessary heat treatments of the mild steels, their grain-size was determined by Jeffries' method, and at the same time some mechanical tests, such as hardness test, tensile test and repeated impact test, were made. The results of these tests were then discussed in connection with the grain-size. They also suggest that the material may be exposed to an unfavorable condition, when it is heated beyond a certain limit of temperature.

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