1915] Michael, ft al.: Hijdrographic Eccards of Scripps Institution 31 



averaged. Assuming other sources of error to be constant (see p. 38), 





 the specific gravity, iS' — , is obtained from the following formula : 

 4 



8^ ^B—[k+a {e°—n°5)] 



4 



where R is the hydrometer reading. 6 the temperature at the time of 

 observation, and A' and a ealibration constants depending upon the 

 particular instrument used. These constants were determined from 

 a series of readings made with each hydrometer on water samples whose 

 specific gravities had previously been measured with a pycnometer. 



An estimate of the accuracy of this hydrometer method was made 

 hy comparing a series of specific gravities determined with a pyc- 

 nometer with those computed from hydrometer readings of the same 

 samples. The following list, for example, shows such a comparison 

 with respect to the values obtained with two hydrometers (nos. 1 and 

 2) each having a range from 1.024 to 1.031, the calibration formulae 

 being 



no. 1, .S'-^ =i?— [0.00167+0.000029 (r— 17?5)] 



no. 2, S - = E— [0.00175+0.000029 (r— 17?5)] 

 4 



List of Comparative Determinations 



Pycuometer No. 1 hydrometer No. 2 hy4lrometer 



