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In making a determination of the H-ion concentration of a solution by the electrometric method, the actual measurement is one of potential difference, or voltage, between a hydrogen and a calomel electrode in contact with the solution. The H-ion concentration, or the Ph value, must then be found by reference to conversion tables or by calculation from an equation.

The H-ion Calculator is a slide rule, which, with one setting, converts the measured voltage into the corresponding PH or Ch+ values. The conversion may be made accurately to the second decimal place.

The Calculator is very quick and convenient in operation. It is made of heavy celluloid, and measures 6 inches by 6 inches.

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SCIENCE

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Repeated object lessons have demonstrated that nearly all progress in science has resulted in important advances in industry

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G-E Research Laboratory

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Among the many products developed by the General
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