Melting Points of Certain Metals. 509 



purpose, we determined, on the standard element, the electro- 

 motive force corresponding to the boiling points of water, 

 naphthalene, benzophenone, and the melting point of. zinc ; 

 while for the temperatures below 100° we compared it with a 

 four-junction element belonging to Dr. W. P. White, the 

 calihration of which is known with an accuracy of a few 

 thousandths of a degree.* The values assigned to the standard 

 temperatures are as follows :f 



Naphthalene b.p 21 7"7° + 0-057 Qo — 760) 



BenzophenoneJ (Merck) b.p... 305-6° + 0-063 (/>— 760) 

 Zinc, m.p 418-2° 



All temperatures given in the present paper are referred to 

 the above fixed points; we also give the actual electromotive 

 forces observed, so that the temperature may be easily cor- 

 rected, if a change in the above reference points be rendered 

 necessary by future work. 



In all the measurements, the cold junction was immersed in 

 an ice-bath at 0°, and the electromotive force was measured by 

 means of the usual potentiometric arrangement. By this means, 

 an accuracy of 1 microvolt, corresponding to 0-02°, could be 

 easily attained. The results thus obtained for the calibration 

 of the standard element are : 



t 



e 

 (^microvolts) 



t° 



e 

 (microvolts) 











ioo-o 



4227 



24-92 



975-7 



217-7 



10119 



50-00 



2012 



305-6 



15007 



75-00 3096 418-2 21755 



Attempts were made to obtain a single equation which 

 should pass through all the points; but without success. 

 Accordingly, two cubic equations of the form e = A + Bt + 

 Cf + Df were used to calculate the electromotive force corre- 

 sponding to any given temperature; e was computed for every 

 10° from 10° to 430° ; the slight irregularities were evened 

 out by adjustment of the successive differences. From the 



*See Phys. Rev., xxxi, 159. Its calibration curve is e = 155-311 t + 

 0-183 f 2 -0-00014( 3 . 



f Cf. Sosrnan, this Journal, xxx, 6. 1910 ; Day and Sosman, ibid, xxix, 93, 

 1910. It is to be noted that up to the present there have been only two gas 

 thermometer determinations of the boiling points of naphthalene and of 

 benzophenone — one by Crafts (Bull. soc. chim., xxxix, 277-S9, 1883) and one 

 by Jacquerod and Wassmer ; the former does not claim an accuracy better 

 than 1°, so that the only accurate data at present available are those of 

 Jacquerod and Wassmer. 



JThe b.p. of benzophenone (Merck), according to Waidner and Burgess 

 (Bull. Bureau of Standards, vii, 6), is 0-2° higher than that of benzophenone 

 (Kahlbaum); the b.p. of the latter is 305-4, according to Jacquerod and 

 Wassmer. 



