It is well known that the electrostatic capacity of a parallel plate condenser is inversely proportional to the thickness of dielectric inserted between its plate electrodes. Then, if we can measure the electrostatic capacity, the thicknes of film is easily deduced from it. We have developed a handy film thickness metter based on this principle, which is now in fairly extensive use in practice. By using an magic'eye as resonance indicator, a coil of 220μH is turned with a variable air condenser (max. 750μμF) to give a resonance at the frequency about 400kc. Connecting a capacitance to be measured parallel to the variable condenser, we retune to find out by what amount its capacity ought to be reduced. This decrase of capacity gives the required value. The capacitance to be measured consists of the two capacitances connected in series which are formed respectively under those two adjacent copper electrodes of 1cm in diameter, wetted with mercury to make good contact to a given filmed metallic article. Thus, if we only put these electrodes on an article from outside, we can quickly get the film thickness without giving any damages in the least. The use of this apparatus is originally intended to measure the thickness of anodic coating of aluminum, but now its use is extending to the field of painting. In this report, some results obtained by this apparatus are given pertaining to the oxide coating of aluminum and painted or sprayed films of various varnishes, paints etc. They show how this apparatus give facility in quality control, inspection or standardization in a mass production procedure.

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In this paper, we studied on the protection methods in the Carbo-Nitriding process of steel, and found that as follows.
1. Using the painting mixture of Al₂O₃ (or SiO₂) and Na₂SiO₃, plating of Zn, Cu, Ni, and Cr, and Al metallizing process, it was found that uing the Al metallizing process was the most effective and reasonable.
2. The utility thickness of the Al metallizing layer was about 1mm., and the protective effect was found when its thickness was more than 1mm.
3. In the investigatiou on the durability of Carburizing salts in which these protection method were used, it was found that the decay of the salt was not recognized using the Al metallizing method.

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We selected several 20-27% chromium stainless steels containing 5% or 10%Ni, 1%Mo & 1%Cu, and researched the influence of heatreatment from 700°to 1100°C and the effect of decreasing chromium content on the acid resisting property in such high chromium steels. Also we researched the influence of sigma phase and various treatment upon the acid resisting property. At the same time, we researched on the influence of heat treatment upon the acid resisting property of several austenite stainless steels which were made in Japan and foreign countries.
The corrosion tests were performed in boiling 5% sulphuric acid. The results are as follows:
1) The addition of Nickel to such high chromium steels for improvement of the acid resisting property must be up to 5%. The high chromium steels containing 10%Ni formed the structure of two phase of α and γ, and so the acid resisting property was inferior to that of steels forming the structure of one phase of α or γ only. Also this steel formed sigma phase easily when heat treated from 700° to 900°C and so the acid resisting property woresened remarkably.
2) The lower limit of decreasing the chromium content is 25% in such high chromium steels containing 5%Ni, 1%Mo& 1%Cu as far as the acid resistivity is concerned.
3) Addition of Molybdenum and Copper improved remarkably the acid resisting property but the presence of Molybdenum resulted in the formation of sigma phase at the condition of long time heating at 800°C.
4) Some surface treatment removed the unstability of the acid resisting property of different charge or heat treatment near 700°C on such high chromium steel which substancially has superior acid resisting poperty.
5) The acid resisting property of austenite stainless steels containing both Molybdenum and Copper showed nearly no change by heat treatment. The weight loss by corrosion of steels which did not contain both Molybdenum & Copper or which contain Molybdenum only increased remarkably when heat treated at the carbide precipitating temperature.

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