'Titanium, and Vanadium by Tliermelectronic Currents. 217 



but there was also as intense a continuous spectrum emitted 

 by the high-temperature tube-furnace, yet, in spite o£ it. the 

 complete iron spectrum, including class III. lines, stood out 

 most brilliantly. 



Now, my observations do not apparently harmonize with 

 the results obtained by Dr. King, who has photographed 

 group 4957 of iron already at temperatures of between 

 1800° and 1900° C, and in one case even at 1650° C.* 

 There can be no doubt that the range of temperatures given 

 by Dr. King's furnace is the same as that available with 

 mine — namely, from about 1500° to 2700° C, and, if the 

 emission of class III. lines of iron were solely controlled by 

 the temperature comprised within these limits, I should most 

 certainly have seen them, or secured them photographically 

 on one or other of the many records taken. The double 

 fact, that class III. lines of iron were not observed in my 

 furnace, nor in the mantles of flames at corresponding* 

 temperatures up to about 2500° C, seems to me to indicate 

 clearly that there must be some other factor present in 

 Dr. King's furnace which is responsible for the emission 

 of these lines at low temperatures. Let us then examine 

 more closely whether there is any fundamental difference 

 between the furnace arrangement used by Dr. King and 

 mine. As will be remembered, my furnace was formed by 

 a carbon tube of 14 mm. internal diameter and an effective 

 length of about 10 cm. The heated portion of the tube was 

 well protected against loss of heat by means of a thick layer 

 of carborundum powder. The heating current supplied to 

 the tube was continuous. The drop of potential along the 

 tube, for temperatures of from 2600° to 2700° C, was about 



1'05 — . On the other hand, Dr. King's furnace consists 



cm. ' fe 



of a tube of Acheson graphite having 12*5 mm. internal 

 •diameter and an effective length of about 20 cm.f The tube 

 is not protected by a carborundum jacket, but is enclosed in 

 -a steel chamber, which is pumped out to a pressure of less 

 than 2 cm. of mercury. Owing to the greater loss of heat 

 through radiation entailed by this arrangement, it requires 

 a larger current to produce the same furnace temperature 

 as with a well protected tube, such as is the case with my 

 furnace. Accordingly, a potential of 30 volts has to be 

 applied to Dr. King's tube in order to bring the temperature 

 to between 2600° and 2700° 0. This corresponds to a 



* A. S. King, Astroph. Journ. vol. xlix. p. 48 (1919). 



t A. S. King, Astroph. Journ. vol. xxxvii. p. 120: ibid. p. 240 (1913). 



