ROSA AND WOLFF: INTERNATIONAL ELECTRICAL UNITS 267 



• Summary 



Mean of 22 experiments, group 1 equals 1 .01828 6 



Mean of 13 experiments, group 3 equals 1 .01828 6 



Mean of 35 experiments, group 4 equals 1 .01833 5 



Mean of 78, giving each equal weight, equals 1.01831 



Mean of 70, giving group 4 half weight, equals 1 .01830; 



There was a difference of opinion among the delegates as to 

 how the results should be weighted in taking the mean, but for 

 the purpose of fixing the value of the Weston Normal Cell to 

 five figures it fortunately makes little difference how the results 

 are combined. If equal weight is given to all, the result is nearly 

 the same as though the weights were unequal. 



The results showed that voltameters in which filter paper is 

 used as septum lead to results which are too high. The delegates 

 were therefore unanimously of the opinion that the results of 

 experiments made under these conditions should not be used for 

 the determination of the value of the emf of the Weston Normal 

 Cell. 



The committee were of the unanimous opinion that ' ' the mean 

 of the results which they have obtained will not be modified by 

 more than several parts in one hundred thousand when the speci- 

 fications shall have been completed. 



"The committee decides to recommend to the International 

 Committee for Electrical Units and Standards the following 

 value for the emf of the Weston Normal Cell : 



E = 1.0183 international volts at 20°C." 



The delegates were unable in the light of the data at hand to 

 agree on final specifications for the voltameter. No time was 

 available for considering specifications for the standard cell. 



The work done clearly established the importance of employing 

 exceedingly pure silver nitrate for the voltameter and the need 

 for suitable tests of purity, as very slight percentages of certain 

 impurities considerably affected the amount of deposit obtained. 



Further work has been in progress in two of the laboratories 

 since the Washington meeting and it is hoped that at an early 

 date, specifications for the voltameter can be agreed upon. There 

 will then remain to be considered similar specifications for the 

 standard cell. 



