Adams and Johnston — Standard Scale of Temperatures. 535 



couples, which were then employed in determining the freez- 

 ing points of the metals tin, bismuth, cadmium and lead.* 

 This calibration has been described in the paper just referred 

 to ; but the account there given must be amplified by the fol- 

 lowing additions and corrections, which are rendered necessary 

 by the slight changes in the temperature scale resulting from 

 the new and more accurate gas thermometer determinations at 

 temperatures up to 500°. 



It has been foundf that too much reliance can not be placed 

 on the readings of copper-constantan thermoelements at the 

 zinc point (419*4°), for some diminution of electromotive force 

 sets in, not serious, but sufficient to preclude the most accurate 

 measurement. For this reason we have ceased to make use of 

 the zinc point as a calibration temperature ; for the same 

 reason, we give the calibration curve only up to about 360°. 



The calibration temperatures, expressed in the corrected 

 scale, together with the corresponding values of the electro- 

 motive force of the standard element, are given in Table I. 



Table I. — Calibration Temperatures. 



t 



e in microvolts 



Difference 



Observed 



Calculated 2 



In microvolts 1 In degrees 















o-o 



o-o 



25*00 



979 



980-0 



— 1-0 



— •025 



50-00 



2012 



2012-7 



+ 0-7 



+ •016 



75-00 



3096 



3095-8 



+ 0-2 



+ •005 



100-00 



4227 



4226-1 



+ 0-9 



+ •019 



217-95 



10119 



10119-3 



— 0-3 



— •005 



306-1 1 



15007 



15007-0 



o-o 



o-o 



1 The benzophenone used was from Merck, which melts (at 46 - 9°) 0'3° 

 lower,' and boils 0'2° higher, than that obtained from Kahlbaum (Waidner 

 and Burgess, Bull. Bur. Standards, vii, 6). The f. p. of our Merck benzo- 

 phenone was also 46"9° ; consequently we have added 0'2° to the accepted 

 b. p. (305'9°) of Kahlbaum benzophenone. 



2 From the equation e=38'105 t +0-04442 & -0-00002856 t\ obtained by 

 the method of least squares, e as measured at the zinc point (419'4°) was 

 21755 microvolts ; the equation gives 21688, which does not differ by more 

 than what one might expect in view of the extrapolation through more than 

 110°. 



To reproduce the above data, a quadratic equation is insuf- 

 ficient, except over a very short range, and so is the cubic 



*Loc. cit., p. 508. 



f Cf. Day and Sosman, preceding paper, p. 521. 



