DAY AND SOSMAN: NITROGEN THERMOMETER SCALE 169 



3. METHOD OF PROCEDURE 



In this apparatus temperatures were read simultaneously (1) 

 upon the gas thermometer, (2) upon three thermoelements dis- 

 tributed at different points in the bath — one in a reentrant tube 

 extending to the center of the bulb, and one each at the top and 

 bottom of its outside wall. 



For the measurements at 4he benzophenone boiling-point, 

 thermoelements of copper-constantan and of platinum-platin- 

 rhodium (Heraeus) were used, for the higher temperatures plati- 

 num-platinrhodium only. After a trial of the copper-constantan 

 elements at the next higher temperature (zinc) evidence of per- 

 manent changes in their readings was obtained which was more 

 than sufficient to offset their increased sensitiveness. They were 

 accordingly abandoned at the higher temperatures. 



Thru the courteous cooperation of the Bureau of Standards, 

 a sensitive resistance thermometer in charge of Dr. Dickinson and 

 Mr. Mueller of the Bureau was placed alongside the bulb during 

 a part of the measurements, and later a similar instrument in- 

 geniously constructed for the purpose by Dr. Dickinson was intro- 

 duced into the reentrant tube of the gas thermometer bulb 

 itself. The resistance thermometer, which was easily sensitive 

 to a few thousandths of a degree, revealed small temperature 

 fluctuations (0?05) in the rapidly circulating liquid* outside the 

 bulb but no systematic temperature differences. Within the re- 

 entrant tube the fluctuations were no longer felt. 



With these precautions to guard against temperature differences 

 about the bulb, temperatures were measured (1) at the boiling 

 point of benzophenone, (2) at the melting point of zinc, (3) at the 

 melting point of antimony. 4 The three thermoelements were 

 then removed from the bath next day and placed in one or other of. 

 the following: in a vapor bath of boiling benzophenone, in an 

 apparatus for determining the zinc melting point, or in a similar 

 apparatus containing antimony; after which they were returned 

 to the gas thermometer furnace for the verification of their read- 



4 The zinc and antimony were the same charges which were used in the previous 

 investigation. The analyses may be found in Pub. No. 157, pp. 87 and 88; Am. J. 

 Sci., 29: 159. 



