Free energy change of the reaction 3Fe+C=Fe3C may be calculated from the heat of formation of cementite at 25°, specific heats of cementite, graphite and iron (α, β, and γ) at 0-1, 100° together with the heats of transformation of A₀, A₂ and A₃ in iron carbon alloy or from the equilibrium constants of the reactions 3Fe+2CO=Fe₃C+CO₂ and 2CO=C+CO₂ at higher temperatures. As these thermo-chemical and dynamical values were measured by many investigators and are in good agreement with each other, in the present papers the free energy change above mentioned has been calculated by using these data. The calculation has been made in two ways according to the following thermodynamical relations, namely, (1) ΔF⁰=-RT ln K_p and (2) ΔC_p=(∂ΔH/ΔT)_p and-ΔH/TT²=[∂(ΔF/T)/∂T]_p, In carrying out the calculation (2) proper correction has been made as the γ-iron dissolves carbon and forms austenite. This has been done by applying the Nernst's formula of dilution i.e. ΔF⁰ (dilution)=-RT ln N₁/N₂. The results of these two ways of the calculation showed a very good agreement with each other, that is, ΔF⁰ of tbe above reaction becomes zero at (1) 960°C and (2) 964°C respectively, and is positive below these temperatures. This means that the cementite is unstable and should decompose into austenite and graphite below these temperatures while above these its decomposition can not take place as it is stabler than the equivalent mixture of austenite and graphite. Hence it may be said that the cementite is meta-stable at lower temperatures but at higher temperatures graphite is meta-stable. By precisely reviewing the experimental data here cited, further calculation of ΔF⁰ of the above reaction has been made by assuming some probable errors or corrections.

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In the metallic arc welding, the welding rod, as well as the welder and welding operator, is one of the most important factors on which success of the welding depends. But the rod is directly and greatly influenced by the welding flux with Which it is coated.
The writers made an investigation of the effects of welding fluxes on the characteristics of the electric arc, using about 30 kinds of ordinary compounds. The result is summarized as follows:
i) When a metallic oxide was used as welding flux, there was observed a definite relation of the atomic weight of the metal to the arc voltage and melting ratio, which varied according to the group of metals as established by the periodic law.
ii) There was a definite relation between the arc voltage and melting ratio irrespective of the property of the welding flux.
iii) Some kinds of welding flux caused a great difference between the values of the arc voltage and melting ratio obtained by connecting the welding rod with the anode and those obtained by Connecting it with the cathode.
iv) The arc voltage and melting ratio yaried according to the chemical composition and physical property of the welding rods. When the rods were coated with a definite kind of welding flux, however, the arc voltage and melting ratio had values which were dependent upon the flux.
Any welding flux which was applied separately showed a definite arc voltage, which was dependent upon its polarity. The value of arc voltage, varying only with the flux, was quite free from the influences of the properties of the welding rod, amount of arc cnrrent, thickness of the coating of flux, etc., and was a factor having the greatest effect on the characteristics of the welding arc. This is a specially noticeable fact Which has been confirmed by the experiment.

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