Nitrogen Thermometer from, Zinc to Palladium. 103 



.erable cooling influence on the central portion of the bottom, an 

 effect which would tend to make their results low. This effect 

 was largely obviated by using, in place of the heavy magnesite 

 tube, a thin Marquardt porcelain tube in the top of which 

 was placed a Marquardt crucible, cut out into a three-pronged 

 support. The bottom of the crucible acted as a screen to pre- 

 vent radiation from the bottom of the bulb, and the smaller 

 thickness and thermal conductivity of the tube practically pre- 

 vented the loss of heat from the bottom by conduction. Later, 

 a second diafram was added, about l cm lower down, primarily 



Fig. 1. 



Fig. la. 



10- 



--H.H 



Section. 



Fig. 1. Numbers indicate the positions of the therm oelements grouped 

 about the bulb. 



Fig. la. A photograph of the bulb made after the palladium-point deter- 

 mination showing all the elements and the diaframs in position. 



for the purpose of centering the tube and bulb in the furnace, 

 but without noticeable effect on the temperature distribution. 

 In addition to the three thermoelements mentioned, a fourth 

 was located inside the reentrant, in position 8.* Several trials 

 under varied conditions confirmed the fact that this element, 

 when the other three were set equal, was 2° to 3° hotter than 

 the one on the outside. A thorough exploration of the dis- 



* See fig. 1, and note, p. 104. 



