File:Transactions (1871) (14592729038).jpg

Identifier: transactionsmining47amer (find matches)
Title: Transactions
Year: 1871 (1870s)
Authors: American Institute of Mining, Metallurgical, and Petroleum Engineers
Subjects: Mineral industries
Publisher: New York (etc.)
Contributing Library: Gerstein - University of Toronto
Digitizing Sponsor: University of Toronto

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ple. As used, it had aresistance of 57 ohms and a period of 2 sec. This sensibility, whichwas ample, could have been increased if necessary. The zero shiftwas not troublesome and the instrument was glass inclosed, reducingtemperature inequalities. The method of operation, whether for cali-bration, inverse-rate or differential curves, was to note time, prefer-ably on the chronograph, and this invariably when taking inverse-rate curves, every time the zero of the scale passed the cross hair ofthe telescope ; the dial of the potentiometer was then turned say twosteps, corresponding to about 2° C, throwing the zero of the scaleback about 25 mm., and the operation repeated indefinitely. Thesensibility is about 0.01° C. with the Pt-Rh thermocouples. The Measurements of Time.—For recording the time measurements,necessary for the inverse-rate method and convenient with the cali-bration and differential methods, use was made of a cylindrical. 680 THE CRITICAL RANGES a2 AND A3 OF PURE IRON.
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THE CRITICAL RANGES A2 AND A3 OF PURE IRON. 681 Geneva motor-driven chronograph together with a telegraph keywhich, when depressed, gave a dash on the chronograph sheet easilydistinguishable from the seconds marks made on the same sheet withthe same pen when actuated through a relay by a standard clock sit-uated in a distant constant-temperature room. The time observationswere easily obtained to 0.1 sec. The Thermocouples.—In some of the preliminary work, variousthermocouples of 0.6 mm. diameter were used, but the later morereliable measurements were all taken with three Heraeus 0.4 X 150mm. thermocouples of platinum, 90 platinum—10 rhodium, markedMv M2, and M3, and all cut off the same batch of wire. Thesecouples were frequently interchanged during the investigation. Adifferential thermocouple, M4, for measuring the difference in tem-perature between the iron sample and the platinum neutral, was madeby fusing a length of 45 mm. of 90 Pt—10 Ir wire between twolengths of platinum

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