Transactions . ause of variation in the rate of heating or cooling of the sample mustbe eliminated. There are two further advantages gained by usingalternating current instead of direct for heating the furnace: it per-mits the use of a liquid rheostat without polarization or electrolysisand it eliminates any magnetic field about the iron sample. Thislast, if present, might conceivably influence the magnetic transforma-tion in iron. The rheostat, Fig. 6, deserves special mention, as it was. speciallydesigned to give automatically a constant rate of heating and cooling,variable at will within wi
Transactions . ause of variation in the rate of heating or cooling of the sample mustbe eliminated. There are two further advantages gained by usingalternating current instead of direct for heating the furnace: it per-mits the use of a liquid rheostat without polarization or electrolysisand it eliminates any magnetic field about the iron sample. Thislast, if present, might conceivably influence the magnetic transforma-tion in iron. The rheostat, Fig. 6, deserves special mention, as it was. speciallydesigned to give automatically a constant rate of heating and cooling,variable at will within wide limits. In addition to wire rheostats asalt-water rheostat was placed in the heating circuit. It consisted of a cypress box of two compartments, each measuring30 by 35 by 35 cm., in each of which were two copper plates (35 by26 cm.), placed 30 cm. apart at the bottom and 1 cm. apart at the metal box through which -cold water was circulated for the purpose 684 THE CRITICAL RANGES A2 AND A3 OF PURE A Marl, tie Bottle B Copper EJeetra/ej C Wedfe D Coolma Boxjps E Calibrated T7p\s F $/fihon G PVater Intel H Water Outlet I Current Lead J Fiber Insulator Fig. 0.—Kheostat. THE CRITICAL RANGES A2 AND A3 OF PURE IRON. 685 of keeping the salt water cool was placed on each side of the outside copper plate in each compartment, besides performing itsfunctions as an electrode, also formed one side of a wedge which openedat the top and could he filled with water before starting a run. Thiswas done to cause the water which was fed at a constant rate from aMariotte bottle to rise between the copper plates at a faster rate as thetemperature of the furnace increased, thus overcoming the greaterradiation losses to which the furnace is subjected at the higher tem-peratures and thereby giving a very constant rate over the whole taking cooling curves the water in the wedges was kept atthe same level as the water in the compartment by connecting thetwo with a
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
