HIGH TEMPERATURE OVEN 209 



AN ELECTRICAL DEVICE FOR SECURING AND MAIN- 

 TAINING CONSTANT HIGH TEMPERATURES. 



W. E. TISDALE. 



In a paper read before this Academy last year, a device for 

 controlling comparatively high temperatures (up to about 600° 

 C) was explained, together with thfj necessary auxiliary appara- 

 tus, an ordinary electro-magnet circuit breaker, and the source 

 of constant potential necessary to operate this magnet. The 

 oven described in that paper consisted of a properly insulated 

 porcelain tube 30 cm. long and 5 cm. in diameter. It required 

 10 amperes to heat it to 450° C. The dimensions of the oven 

 limited the size of the tubes in which the crystals were to be pro- 

 duced to not more than 3 cm. in diameter and 15 cm. in length, 

 and admitted but one at a time. Inasmuch as it requires sev- 

 eral months to produce crystals of a size such as is necessary 

 for optical and electrical work, the disadvantage of the oven 

 may be readily seen. 



In the catalogues of the various manufacturers of regulated 

 electrical ovens, there are no descriptions of ovens that go above 

 300° C, so that the only method of obtaining one that, would suit 

 our purposes was to manufacture it ourselves. 



Accordingly, the oven shown in figures 24* and 25 was de- 

 signed. Except for the angle irons used in the corners, and the 

 necessary bolts, it is made entirely of asbestos board three- 

 eighths inch thick. The oven is double walled, the interspace on 

 the sides being filled with loose asbestos, and that on the top 

 with air. The inside dimensions are 12x12x14 inches, the longer 

 dimension being the height. In figure 24 an elevation view is 

 shown. The asbestos board with the double row of holes shown 

 at the left in the figure is the bottom of the oven space, and be- 

 longs immediately above the heating coils, which may be seen 

 in place on the bottom. The top shown tipped up is the top of 

 the oven space, and between it and the top of the entire ap- 

 paratus (shown in the front of the oven) is a space of three 

 inches of air. The thermometer is seen projecting at the left. 

 and on the inside the controlling device (figure 26) is seen in 

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