ROSA, VINAL, AND McDANIEL! SILVER VOLTAMETER 53 



ing the committee's work and to make such other experiments 

 as might afford data for the voltameter specifications, not yet 

 adopted. 



The International Committee fixed the voltage of the cell to 

 five significant figures (1.0183 volts at 20°C.), but it is desirable 

 to reach an accuracy sufficient to justify recording six figures, 

 since the voltameter is a primary standard. Results are ex- 

 pressed as the voltage of the Weston Normal Cell at 20° computed 

 from the defined electro-chemical equivalent of silver, 1.11800 

 mg. per coulomb. 



The procedure was according to the best methods learned from 

 previous work. In all cases the electrolyte was carefully tested 

 for its purity and the acidity determined. The voltameters 

 used were chiefly the porous pot and Smith's form, but on several 

 occasions we used the siphon form, the modified ring-shaped 

 siphon, and the Poggendorff form. 



Since we had learned from previous work that the effect 'of acid 

 in pure electrolyte is to lower the deposit, we sought to find if 

 possible a quantitative relation between the amount of acid, ex- 

 pressed in equivalents of HNO3 per million, (X) and the decrease 

 in deposit, also expressed in parts per million, (F). As a result 

 of a large number of comparisons of neutral voltameters with 

 others made acid by varying amounts we have found the following 

 relation 



Y = -4.5X + 0.02X2 



which we think is justified by the figures given in the complete 

 paper.i 



For acidities below 10 parts per million the square term is of 

 course unnecessary. The above equation was used in comput- 

 ing a correction to each deposit, but this correction was very small 

 in all cases for the results given below. The result of 156 deposits 

 in the porous cup form is: 



1.01826- volts 

 The average deviation of a single observation from the mean is 



1 Von Steinwehr's recently expressed opinion to the contrary (Instrumenten- 

 kunde, November 1913) was based on earlier work which was not so conclusive as 

 our recent work. 



