File:Transactions (1871) (14586574277).jpg

Identifier: transactionsmining23amer (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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f the thermo-j unction may differ very considerably fromthat of the bar under treatment. It does not suffice simply to lay the junctioji against the bar, unlessthe latter be at the same temperature as the surrounding atmosphereand walls. If it be not, then the junction will be at a temperatureintermediate between that of the bar and that of the surroundingobjects. It is difficult to have the bar and the surrounding objectsat the same temperature, unless a muffle be used; and even with amuffle it is possible only when the temperature is stationary or atmost moving very slowly. But by imbedding the junction betweentwo like bars, which are under like conditions as regards heat, itstemperature is but slightly affected by that of other objects. Never-theless, even with the arrangement shown here, the influence of thewalls of the inner muffle is not wholly effaced during rapid changesof temperature. The galvanometer shows at any moment the temperature of the 536 THE HEAT-TREATMENT OF STEEL.
Text Appearing After Image:
fcT & THE HEAT-TREATMENT OF STEEL. 537 therrao-junctiou itself, unless the leading-in wires be short-circuited ;if they are, the galvanometer shows their temperature at the point ofshort-circuiting. Now the leading-in wires, small though they be,are good conductors of heat, and with the very great differences oftemperature which often exist between neighboring parts of appa-ratus for high-temperature experiments, they may conduct enoughheat to the thermo-j unction or away from it to affect its temperatureseriously. For instance, it was actually found that, if the double-bored clay tube, O, was broken, so that the leading-in wires were ex-posed to the flame, they conducted so much heat to the thermo-junc-tion that the readings of the galvanometer were much too high. Oncutting off the gas the temperature of the couple would drop 4° oreven 6° instantaneously, clearly because the wires, superheated bythe naked flame, had been conducting heat to the thermo-junction,and raising its te

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