Abstract

High Temperature Thermometers. The thermometer resembles that of the mercury in glass type but is graduated to 1000°C. It uses fused quartz as the container and the rare metal gallium as the filling liquid.

The paper includes a brief description of the Properties of Gallium with reference to its use in thermometers. Gallium is the only metal with a low melting point (29.7°C) and high boiling point (1500–2000°C). Together with these unusual properties and that of undercooling (−20°C or below) which makes it an ideal thermometric liquid if it were not for the tendency to wet glass and quartz surfaces.

The experimental investigation recounts the method for overcoming the wetting property whereby additional information was obtained on the properties of gas solution; surface oxidation, undercooling of liquid gallium and the effect of impurities on increasing the wetting property.

The filling operation in preparing the thermometer and the successful method of etching quartz and marking the graduations are briefly described.

© 1926 Optical Society of America

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