GALLIUM IN QUARTZ

Hawera Star, Volume XLVI, 8 January 1927, Page 10

GALLIUM IN QUARTZ

LATEST THING IN THERMOMETERS. CAPABLE OF REGISTERING VERY HIGH TEMPERATURES. A thermometer, similar in appearance to the usual mercurv-in-glass thermometer,v but capable of registering a temperature of more than. 1800 (leg. Fahrenheit, has- been invented. Instead of glass, which would melt at far lower temperatures, the thermometer bulb and stem are made of clear fused quartz; and instead of mercury, which would boil and cause the thermometer to explode at such a temperature, gallium, one of the rare metals, is used. A temperature of 1000 deg. Fahrenheit is the maximum with the mercury-in-glass thermometers, and at such high temperature they are inaccurate (states The Digest). By the use of mer-cury-in-quartz,, German scientists attained a previously maximum temperature reading of about, 1300 degrees Fahrenheit. The ordinary household thermometer depends upon a vacuum in the stem above the mercury, and the usual hightemperature instrument uses gas underpressure in the. .stem. The new gallium thermometer returns to the first principle, with a vacuum or only slight amount of gas above the registering column. The discovery of a method for tire commercial production or clear fused quartz as tubing was the important development that made the new instruments possible. The other necessary study was in regard to the physical and chemical properties of the rare metal, gallium. This metal is similar to mercury in appearance, but is much lighter in weight. It melts at a temperature of 100 degrees Fahrenheit, but can be cooled to about 40 degrees before solidifying. Gallium boils at about 8600 degrees, so that it is not necessary to have it under pressure in the thermometer; In making the thermometers it is necessary to have the gallium very pure, since slight traces of certain impurities so affect the metal -that it .-•ticks To or ; wets" either glass or quartz. ‘‘Wetting” makes a metal unsuitable for use in thermometers. It was therefore necessary for the company’s scientists to investigate the properties of the metal before a proves- could be developed whereby the pure gallium could be obtained within tic- stem o ; the thermometer. liven further research was necessary, however, since it. is not possible to etc-li the .scale marks on quartz in the way that glass is etched in thermometer manufacture. It was found that cold hydro-fluoric acid, used for glass, ; attacks the entire quartz surface in spite of protective coatings. The etching was accomplished by using hot 1 dilute hvdro-fluoric acid, with a very i special oil as a protective coating. To «

—WB—mm ■ WWWM———MIIM! ■ \ make the scale easily visible a composition of sand and copper oxide is used to produce grayish black marks; this substance not only withstands the intense heat, but also resists most chemical reagents. Such devices a-s thermocouples and pyrometres have been resorted to heretofore for high-temperature readings. The new thermometer permits accurate high-temperature determination in the same manner as ordinary thermometers record moderate temperatures. One advantage of the use of quartz is it- low co efficient of expansion. It is not affected by sudden changes of temperature such as would shatter glass. Gallium-in-quartz thermometers are the latest or a number of instruments made possible by clear fused quartz. Other recent developments have included quartz lenses for motion picture projectors. improved astronomical mirrors, a large variety of medical and surgical instruments, and quartz window panes for securing the medical effect of ultra-violet light from ordinary sunshine.