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MR. W. R. BOUSFIELD AND DR. T. M. LOWKY OX THK ELECTRICAL 



difference curves had the advantage that they could be plotted on a larger scale than 

 the densities, and they were found to be much simpler in form than the sensitive 

 curves described in Part II. of the paper. Where measurements of density had not 

 been made at the exact temperatures chosen for the isothermal curves, values for 

 these temperatures were calculated by means of the cubic or quadratic formulae 

 described in the preceding paragraph ; the interpolated values, being based to some 

 extent on the whole series of measurements, were at least equal, and probably 

 superior, in value to the individual observations of the series. The difference curves 

 served the double purpose of bringing into relief the experimental errors in measuring 

 the change of density with temperature, and of providing a means of deducing by 

 interpolation the densities for exact percentages at the exact temperatures chosen. 



TABLE VII. Soda Densities, Observed and Calculated. 



