BRIDGMAN. 



A SECONDARY MERCURY RESISTANCE GAUGE. 



243 



would be beyond the accuracy of this work. Table VI shows the value 

 of p computed by the formula for the two extremes of the temperature 



TABLE VI. 



Temperature Correction for Pressure in Terms of Resistance. 



range. The observed pressures tabulated are the pressures computed 

 from the change of R 7 after correction is applied reducing to soft 

 glass. The difference column really contains, therefore, two sources 

 of error. The differences are fairly small and irregular in sign. * The 

 irregularity is doubtless due to the incomplete seasoning of the glass 

 by the previous single excursion through the pressure range, and the 

 less regular behavior of the comparison resistance in the hard glass 

 capillary. 



During the preliminary comparisons of different mercury resist- 

 ances, the effect of a known slight quantity of impurity in the mercury 

 was determined. The numerical values thus obtained are given here, 

 as they may be of interest as showing the degree of purity which it is 

 necessary to attain. It was found that metallic impurities have the 

 greatest effect. Impurities that may be absorbed from the glycerine 

 and water unavoidably in contact with the mercury appear to have 

 no effect, as is shown by the constancy of behavior of the gauge over 



