THE 



AMERICAN JOURNAL OF SCIENCE 



[FOUR T-H SERIES.] 



Art. XXX. — The Melting Points of Minerals in the Light 

 of Recent 'Investigations on the Gas Thermometer / by 

 Arthur L. Day and Robert B. Sosman. 



When the work of the Geophysical Laboratory was begun, 

 no temperatures above 1150° C. had ever been accurately 

 measured with the nitrogen thermometer. It had been the 

 custom of the Reichsanstalt to interpret the readings of a 

 thermoelement above 1150° by first calculating the curve of 

 temperature and thermal electromotive force of the element 

 for the region between 400° and 1150°, and then extrapolating 

 this curve. The fixed temperatures commonly printed on high- 

 temperature measuring devices, like the Siemens and Halske 

 direct-reading galvanometers, are based on this extrapolation. 



The absolute accuracy of the Reichsanstalt scale (400° to 

 1150°) was estimated to be about 3° at 1150°, and the extra- 

 polation above 1150° with the thermoelement is certainly in 

 error by more than ten times this amount at the melting point 

 of platinum. It was therefore deemed necessary to undertake 

 a new investigation of the high temperature region with the 

 gas thermometer, and in particular to extend its range for a 

 considerable interval above 1150°, in order that a sound basis 

 might be established for the mineral work of this laboratory. 



Accordingly, such an investigation was begun in 1904, and 

 the final results were published within the past year.* It 

 proved possible not only to attain higher accuracy in the region 

 between 400° and 1150°, but to extend the fundamental meas- 

 urements to 1550° with an accuracy estimated at 2° at the 

 latter temperature. 



In the meantime, the temperature measurements made in 

 this laboratory with thermoelements had been interpreted in 



* Preliminary publication : Day and Clement, this Journal, xxvi, 405-463, 

 1908. Final publications : Day and Sosman, this Journal, xxix, 93-161, 

 1910 ; E. B. Sosman, ibid., xxx, 1-15, 1910. . 



Am. Jour. Sci.— Fourth Series, Vol. XXXI, No. 185. — Mat, 1911. 

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