CELLS AND MANOMETER ATTACHMENTS. 13 



that current will eventually maintain in the furnace. In the case 

 of the instrument here mentioned, from 7 to 9 hours were required 

 for that purpose. A close regulation of the temperature was there- 

 fore impossible. Another objection to this furnace was its waste- 

 fulness. At 1250° the consumption of electrical energy was equivalent 

 to 1200 watts. The furnace was improved to some extent by certain 

 modifications which were introduced, but not sufficiently to justify its 

 continued use. It was therefore abandoned for one of our own con- 

 struction,* in which the wires were all exposed in the space to be heated. 

 The saving in electricity thereby effected was over 50 per cent. The 

 new furnace is shown in Figures 5 A, 5 B, 5 C, and 6. It will be seen to 

 consist (Figure 5 A) of platinum wires threaded through three clay rings 

 (a, b, and c), which are held apart by three platinum rods. The rods 

 expand in the same degree as the wires, and thus keep the latter taut, 

 whatever may be the temperature of the furnace. Otherwise the wires 

 would "buckle" and short circuit at high temperatures. The wires are 

 in two pieces of equal length, so that they may be placed in series or in 

 parallel, according to the amount of current which it is desired to use. 

 Figure 5 B shows the furnace in place in the innermost (d) of the clay 

 cylinders which surround it when in use. The cover (e), the bottom 

 (/), and the truncated cones (g) on which the furnace rests are also 

 represented in the figure. Figure 5 C represents the outer clay cylinder 

 and its various accessories. In Figure 6 all the parts, lettered as in 

 Figures 5 A , 5 B, and 5 C, are assembled as a crucible furnace. The outer 

 covering (m) is a sheet-iron cylinder, which is covered, internally and 

 externally, with asbestus paper. The purpose of the remaining parts 

 (n, o, p, q, r, and s) is obvious without explanation. 



The electric kilns (of which three were usually in operation) were all 

 calibrated by means of a Le Chatelier pyrometer. They thus became, 

 in themselves, resistance pyrometers, the temperature of which could be 

 easily ascertained at all times. The electric kilns answered well the 

 purpose for which they were constructed up to about 1200°, i. e., to a 

 temperature at which platinum begins sensibly to volatilize in an 

 atmosphere containing oxygen. At higher temperatures, the loss of 

 platinum was sufficient to make an occasional recalibration necessary. 



The best results were obtained at about 1300°, i. e., between the 

 melting-points of Seger cones Nos. 8 and 9. Having ascertained the 

 most advantageous temperature for burning the cells, there was no 

 longer any good reason for baking them in the laboratory rather than 

 at the pottery. Fortunately, at the opportune time, we were offered 

 the free use of the kilns of the Chesapeake Pottery Company by the 

 late president of that concern, Mr. D. F. Haynes. A similar courtesy 

 was also extended to us by the Bennett Pottery Company. At the 



*Amer. Chem. Journal, xxxu, 93. 



