. The melting points of fire brick . p. 712, 1901; Ann. , 10, p. 225; 1902. Waidner and Burgess: Bull. Bureau of Standards, 1, No. 2; 1904. Mendenhall:Phys. Rev., 33, p. 74; 1911. Henning: Zs. f. Instrumentenkunde, 30, p. 61; 1910. Kanolt] Melting Points of Fire Bricks mm. The crucibles were heated or cooled gradually, while obser-vations were made every 10 to 20 seconds, and the resulting heatingor cooling curves were plotted. A typicalcurve is shown in Fig. 3. In this diagram achange of temperature of 1 ° corresponds toa change of current of about means of the three k
. The melting points of fire brick . p. 712, 1901; Ann. , 10, p. 225; 1902. Waidner and Burgess: Bull. Bureau of Standards, 1, No. 2; 1904. Mendenhall:Phys. Rev., 33, p. 74; 1911. Henning: Zs. f. Instrumentenkunde, 30, p. 61; 1910. Kanolt] Melting Points of Fire Bricks mm. The crucibles were heated or cooled gradually, while obser-vations were made every 10 to 20 seconds, and the resulting heatingor cooling curves were plotted. A typicalcurve is shown in Fig. 3. In this diagram achange of temperature of 1 ° corresponds toa change of current of about means of the three known temperatures,the relation between the current in the lampand the temperature was expressed in theform, C = a + bt + cf. This method presented two possiblesources of error to be especially considered,namely, the conduction of heat along theinner graphite tube, and the departure of the interior of this tubefrom black-body conditions. If the conduction of heat along thetube introduced appreciable error, the observed temperatures. .50 \ \ \ ^ r > 0 r k u v .49 .47 4MINUTES Fig 3.—Calibration of lamp at freezing point of silver would be too high with rising temperature, when the furnace heaterwould be hotter than the metal, and too low with falling tempera-ture, when the reverse would be true. The fact that the resultsfrom the heating curves obtained with copper and silver were invery close agreement with those from the cooling curves showsthat the errors from conduction are negligible; and these and i o Technologic Papers of the Bureau of Standards [No. JO numerous other observations have indicated that such a tubewhen made of graphite, which is itself nearly perfectly black, is avery good black body. Using the copper-silver eutectic somewhatunsatisfactory results were obtained with heating curves, the troubleappearing to be in the behavior of the alloy rather than in the tem-perature measurement. In this case only cooling curves were usedfor the calibration. The calibra
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