By adding fluorspar to molten iron, the cast iron having spheroidal or globular form of graphite and having high ductility was obtained.
  The cast iron added 5.0% fluorspar have shown good mechanical properties, for instance, tensile strength of 37.6 kg/mm² and elongation of 8.0% as cast.
  The suitable pig iron for this treatment was the iron of composition above S. C. I. I. or high silicon pig iron.
  To obtain the excellent mechanical properties, the amount of fluorspar as much as 5.0% is needed and high temperature must be maintained at the period of addition.

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  It has been understood from the results of the experiments heretofore carried out by the authors that shrinkage cavity is apt to occur when the molten iron is oxidized and that the inclement of SiO₂, as an inclusion, is found simultaneously by the chlorine method for oxide determination.
  In order to clear up the relation between sirinkage cavity and the inclusion, the experiments this time were made to discriminate the form of SiO₂ and the effect of that form on the graphite structure were also studied.
  The electron diffraction method was applied to discriminate the form of SiO₂. On the plane of the oxidized iron specimen etched with bromine gas, the electron diffraction reflection pattern like α-crystobalite was observed indistinctly.
  This specimen was subsequently treated by chlorine gas of high temperature and then the residue drawn out from this treatment, the non-metalic substance, was investigated by the electron diffraction transmission method.
  This time, the diffraction transmission pattern of α-crystobalite was observed very clearly.
  In the case of treating the silicate, like 2FeO·SiO₂, with chlorine gas, however, no transmission pattern of α-crystobalite was observed. Consequently, it has been confirmed that the SiO₂ obtained from the oxidized specimen has the form of α-crystobalite and that the specimen does not give the form of the double salt with FeO.
  In the next step of the experiments, turning scrap of cast iron was melted in contacting with silicate powder, FeO powder and various sorts of SiO₂-FeO silicates and the influence of those substances on graphite structure was investigated.
  The results taken are as follows :
 1) Pure silica impedes the graphitization when it contacts with molten iron.
 2) It seems that FeO and SiO₂-FeO silicates also impede the graphitization. But, this can not be said confidently because the percentages of carbon and silicon in the iron decreased somewhat.
 3) When the molten iron is oxidized at relatively low temperature, the percentage of SiO₂ becomes greater.
  Therefore, in order to explain the cause of the occurence of shrinkage cavity, it will be necessary to confirm the effects of SiO₂ which seems to impede the graphitization. (H. M.)

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  This is the result of the experiment to clarify the influences of moisture content, grain size distribution, bentonite addition and etc. upon green surface hardness and its variation.
  As to green surface hardness, its occurrence due to several combined factors having interaction was discussed.
  As to green hardness variation, the relation between these factors affecting green surface hardness and hardness variation, i. e., oscillating and decreasing tendency of green hardness variance was also discussed and then from these results, changing phases of grain bonding structure were induced.
  Furthermore, the relation between the mean variance of hardness and the bentonite content was explained.

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    In the previous report, the author has clarified that the grain shape of silica sand could be determined quantitatively by the air permeability method.
    The grain shape of silica sands for steel castings, yielded in Aichi and Gifu district, was studied this time and the influences of the methods of sand preparation on the grain shape were also examined by the air permeability test.
    The results obtained are as follows :
  (1) The coefficient of angularity of silica sand for steel casting yielded in Aichi and Gifu district was in the range of from 1.25 to 1.81 and the average coefficient of angularity was 1.28 to 1.56.
   (2) The grain shape of sands prepared by the conical milling or by washing and screening methed was much more spherical than that of natural sands.

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