Electrochemical and metallurgical industry . inversely pro- 136 AND METALLURGICAL INDUS TRY. | Ill, No. 4. portional to ilioir resistances, the latter should be inverselyproportional to the heating surfaces. If r, is the resistanceof the upper, and r, the resistance of the lower resistor,tlien n 53-2 r> 437 = Therefore the proper thickness for the ui)i)er resistor would be3-2 = 2.() cms. Still another complication exists, for hitherto we have that the resistivities of both resistors would be thes;ime. This, however, will not he the case, for
Electrochemical and metallurgical industry . inversely pro- 136 AND METALLURGICAL INDUS TRY. | Ill, No. 4. portional to ilioir resistances, the latter should be inverselyproportional to the heating surfaces. If r, is the resistanceof the upper, and r, the resistance of the lower resistor,tlien n 53-2 r> 437 = Therefore the proper thickness for the ui)i)er resistor would be3-2 = 2.() cms. Still another complication exists, for hitherto we have that the resistivities of both resistors would be thes;ime. This, however, will not he the case, for the resistivityof the lower resistor will he less than that of the upper re-sistor, because of the greater pressure on the former by themnfHes and their contents. This effect cannot be calculated,so it seemed best to leave the determination of the size forthe upper resistor to experiment. Alterations in the upper re-sistor could easily be made by removing the top of the fur-nace. In Fig. .1 there is shown a general view of the .vmufHe fur-. FIC. 3.— VIEW OF FURNACE. race. The three bricks projecting from the side wall of thefurnace indicate the position of the muffles, as these could beremoved so that the interior of the muffles might be lK)tt<)m of this furnace was only 7 cms. thick, and it wasobserved that after a nui of a few hours the loss of heatthrough the bottom was very great, hence, a considerablygreater thickness was used in building the next furnace. Thefirst stage in the construction of the furnace now under con-sideration is shown in Fig. 4. The lower resistor is in place,and the five muffles, the openings into the latter being scoop is lying on the top of the muffles In Fig. 5 issh<)wn the same side of the furnace as in Fig. 4 after thebuilding was finished. In Fig. 6 the other side of the furnaceis shown with the rod h projecting and connected with the\oltmeter. At the left side is shown the regulating resistorwith bricks l
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