This thickness gage measures the force necessary to overcome the magnetic attraction between the precision formed magnetic needle in the gage and the magnetic base material. The essential part of this gage is a magnetic needle, which is made of iron of high magnetic permeability and is fixed so as to be perpendicular to the coating to be measured. This needle is magnetized and attracted upward by the moving permanent magnet placed at the other end of the needle. To measure the thickness first the position of the permanent magnet is changed by turning the barrel. Then, the needle over the film is magnetized gradually by the moving permanent magnet. When the magnetic attraction of the magnet for the needle becomes larger than the force holding the needle to the surface to be tested, the needle with the indicater rod connected to it jumps saddenly apart separately from the film and the indicater extends above the top of the gage, which provides accurately the definite end point indication. It was found that the moving distance of the magnet is proportional to the thickness of the film.
The gage is calibrated with standard coating of known thickness. From the graduation marks on the barrel of the gage, the thickness is read directly. To rest the needle, depress the rod with the gage-end firmly against the surface to be measured.
This gage will determine coating thickness in the range from 0.002mm up to 0.5mm. In this report the effect of the magnetic properties of the base metal, the aging effect of the needle and the magnet and the error problem are also discussed.

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In the previous paper [Light metals, No. 3 (1951-V), No. 7 (1953-V), and No. 8 (1953-8)], the electro-chemical properties of Aluminum-Magnesium Alloys was reported.
This paper deals with the rerearches on the electrode potential and the hydrogen evolution of 52S.
Samples were the rolled alloy plates of 40%, 70% and 90% reduction, and then heated at 100°C and 200°C respectively. After heat-treatments, Samples were dipped in the electrolyte of 5%, 10%, 20% and 30% HCl and then the hydrogen-evolution was measured of the character of oxide films produced on aluminum-magnesium alloys in the electrolyte of 5% HCl, 5% HCl+1% K₂CrO₄ and 5% HCl+5% K₂CrO₄, was examined respectively by the electro-diffraction method.

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Cu plate for printing is generally etched with ferric chloride. In place of ferric chloride, we used nitric acid which is cheaper, and could measure the degree of deterioration more easily. We found that 20% HNO₃ solution containing 4 to 5% NaNO₂ had more excellent etching rate than 38° Be FeCl₃ solution. However, it appears that 10% HNO₃ solution containing 5% NaNO₂ is more suitable for actual etching of Cu plate for printing.

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In order to produce the film of strong adherance, the metal surface is desired to be cleaned and ronghened by possibly simple pretreatment. The authors tried several methods of pretreatment-sand-blasting, sandpaper-polishing, acid pickling and phosphate pickling-and found that sand-blasting was superior and phosphate pickling was nearly as good. as sand-blasting, while sandpaper-polishing was undesirable.

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Many chromium plated articles are often used at high temperature. In these cases various phenomena occur providing advantages or disadvantages for use. The diffusion which occurs between an electro-deposited metal and a base metal is one of the important phenomena. In the present work, pure iron directly chromium plated has been heated in a vacuum, and then the diffusion coefficient and the activation energy have been calculated.

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