526 Day and Sosman — Nitrogen Thermometer Scale 



Material of the bulb : pure platinum 80 per cent 

 pure rhodium 20 per cent 

 Volume of bulb: F =205*82 cc 

 Volume of unheated space: v 1 = , 309 cc 



^r =0'00150 



Expansion coefficient of bulb material: 10 6 ^=8*79 + 0*00161 t 

 Gas: pure nitrogen. 



Initial pressure of gas (see Table I): /> =about 500 mm . 

 Pressure coefficient of gas (see Table II) : a = 0*0036679 to 

 0-0036681. 



Formula used in the computations: 





in which p and p are the corrected pressures at 0° and t respec- 

 tively. 



5. Experimental Results with Nitrate Bath. 



Table I contains the measurements of the zero-point of the 

 instrument before and after each heating and serves to show 

 that its variations are wholly within the accidental errors of 

 reading of barometer and manometer. In the third column 

 p\ is the measured initial pressure of the gas in millimeters 

 of mercury at zero degrees. The application of the correction 

 for the "unheated space" gives the pressures (p ) of column 4. 



The measurements included in Table II are introduced 

 merely as a rough check on the pressure coefficient (a) of the 

 gas. A much more accurate determination has been made of 

 this constant for nitrogen by Chappuis* and his value of it 

 (0*0036681, corresponding to a pressure of 502 mm ) was used in 

 the calculations which follow. These measurements merely 

 afford a rough confirmation of this value within the somewhat 

 larger limits of error of our instrument. Columns 3 and 4 

 cdntain the pressures at the boiling point of water corrected as 

 in Table I. 



In Table III, columns 3 and 4 contain the pressure measure- 

 ments near the three fixed temperatures of reference, reduced 

 as before ; t (column 5) is the gas thermometer temperature in 

 the nitrate bath and e (column 6) the corresponding electromo- 

 tive force of the thermoelement in microvolts ; e (column 7) is 

 the electromotive force of the same elements in benzophenone, 

 zinc and antimony respectively and the final column contains 

 the corresponding gas thermometer temperatures. 



*Trav. Mem. Bur. Int., vol. xiii, 1907. 



