76 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



electric current, and to make spectrophotometric comparisons of the 

 visible radiation from their surfaces with the corresponding wave lengths 

 in the spectrum of an acetylene flame. 



The carbons used for this purpose were produced by the well-known 

 process of squirting a semi-fluid carbonaceous paste through a cylindrical 

 opening. They were straight cylindrical rods 10 cm. in length, and 2 mm. 

 in diameter. Still larger rods would have been preferable, but I was 

 unable to obtain any of greater diameter than the above that were capa- 

 ble of withstanding the temperatures to which it was necessary to heat 

 them. The rods were mounted horizontally in a massive metal box 

 40 cm. in length, 20 cm. wide, and 20 cm. in height. This bos, which was 

 made especially for this investigation, had openings at the ends, through 

 which, by means of air-tight plugs, the terminals of the carbon could be 

 introduced. Through one of these plugs, likewise, the platinum and 

 platinum-rhodium wires of the thermo-element, by means of which the 

 temperature measurements were made, entered the box. In one of the 

 vertical sides of the box was a row of five circular plate-glass windows, 

 which could be removed for cleaning, through which the carbon could be 

 seen and the spectrophotometric observations couVl be made. Other 

 openings in the top of the box and through the opposite sides served to 

 connect it with a mercury air pump of the Geissler type and for the 

 introduction of manometers for the measurement of pressure. A vertical 

 cross-section of this part of the apparatus is shown in Figure 1. Attempts 



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Figure 1. 



