118 A. L. Day and R. B. Sosman — 



wire into contact with an uncontaminated one in a blast flame 

 (temperature, 1460-1500 u ), the cold junction being maintained 

 constant at 0°. The absolute magnitude of the numbers in the 

 column "before heating" represents the electromotive force 

 between two uncontaminated platinum wires of (nominally) 

 equal purity. Its constant value is a measure of the homo- 

 geneity of the new wire. Its departure from this constant 

 value " after heating " is a measure of the contamination it has 

 received. Slight irregularities are the result of variations in 

 the blast flame temperature. Such observations merely serve 

 to furnish information about the distribution and approximate 

 amount of contamination received by the element, but do not 

 of themselves provide the data to correct its reading in a par- 

 ticular furnace. 



Integration of Temperatures over the Bulb. — By the method 

 which has been already described (p. 104) the differences of 

 temperature between the ends of the bulb and the middle were 

 determined differentially by means of platinum wires attached 

 to the bulb itself. Temperatures about the circumference 

 were measured by separate thermoelements, as it was not practi- 

 cable to measure these differences differentially because of the 

 necessity of passing a platinum binding wire around the bulb 

 to hold the four elements in position. A check on the accu- 

 racy of this differential method was obtained by using in one 

 case a thermoelement at the top shoulder of the bulb and 

 thus measuring the temperature at this point both directly 

 and differentially by means of the platinum wire of this ele- 

 ment. The two temperatures agreed within 0'8° when the 

 deviation from the middle was 6° ; when the temperatures at 

 the middle and top were nearly equal, the two methods agreed 

 to 0-1°. 



AE 



Table III contains values of , the rate of change of E.M.F. 



At ' & 



with temperature at various temperatures from 400° to 1500°, 

 both for the 10 per cent rhodium alloy and for the 20 per cent 



AE 

 Table III. — Values of for the alloys 90 Pt. 10 Ph. and 



80 Pt. 20 Rh. 



Temp. 90 Pt. 10 Rh. 80 Pt. 20 Rh. 



400° 9-4 11*5 



600° 10-1 12-8 



800° 10-8 14-2 



1000° 11-4 15-6 



1200° 11'8 169 



1400° 12-2 17*5 



1500° 12-4 17*8 



