Nitrogen Thermometer from Zinc to Palladium. 119 



alloy of which the bulb was made. The data for the 20 per cent 

 alloy (which need be only approximate) were obtained by two 

 methods : (1) An element was made up by combining a plati- 

 num wire with the 20 per cent rhodium bar used for the 

 expansion coefficient determination, and its readings compared 

 directly with those of a 10 per cent rhodium element in the 

 melting point furnace. (2) A. platinum wire was connected 

 from the stem of the gas thermometer bulb outside of the gas 

 thermometer furnace to the ice box, and the E.M.F. deter- 

 mined against the standard platinum wire attached to the 

 middle of the bulb. In both cases, the E.M.F. of the junction 

 of platinum with the rhodium alloy at room temperature was 

 applied as a correction. 



In order to obtain the true E.M.F. corresponding to the 

 temperature as measured by the pressure of the gas in the bulb, 

 it is necessary to integrate the various readings over the sur- 

 face of the bulb. The following arbitrary weights were given 

 to the different positions of elements on the surface : 



Top axis 



(position 



1) 



5 



Top shoulder 



( " 



2) 



20 



Middle 



( " 



4) 



55 



Bottom shoulder 



( " 



6) 



15 



Bottom axis 



( " 



*) 



5 



The elements on the axis at both top and bottom, although 

 sometimes deviating rather widely from the others, have com- 

 paratively small weight, as they affect only a small portion of 

 the total volume. The element at the lower shoulder of the 

 bulb is given less weight than that at the top because of 

 the smaller volume of the lower half, due to the presence of 

 the reentrant tube. 



It was easy to show experimentally that it matters very little 

 what these relative weights assigned to the different readings 

 may be, since the total correction was usually small. In a 

 number of cases, two different settings of the temperature dis- 

 tribution were made at each temperature, one in which the ele- 

 ments at the top and bottom shoulders of the bulb were made 

 equal to the middle, and one in which the elements at top and 

 bottom on the axis of the cylinder were made equal to the 

 middle. The pressures corresponding to these two settings, 

 reduced to the same reading of the standard element, are 

 shown for several typical cases in the table below. 







Pressure when 1, 



Pressure when 2, 







4, and 7 were 



4, and 6 were 



Date 



Temp. 



equal 



equal 



22 Jan. 1909 



1082° 



1038'82 mm 



1038-64 mm 



2 July 1909 



1395° 



1285-43 



1285-17 



17 Sept. 1909 



1489° 



1331-40 



1330-63 



