MEASUREMENT OF SALINITY OF SEA WATER 11 



national de la Mer. This apparatus is used by the United States 

 Geological Survey, the Bureau of Fisheries, and other organizations. 

 The outfit is described briefly by Dole and Chambers in Carnegie 

 Institution Publication No. 213, 1918, page 309, as follows : 



An essential part of the apparatus is a calibrated burette so graduated that 

 its reading is approximately grams per kilogram of chloride if 15 c. c. of sea 

 water is titrated with a solution containing about 37 grams iter liter of silver 

 nitrate. A float in the burette assists in estimating tenths of the smallest 

 divisions. The strength of the standard solution of silver nitrate is determined 

 by carefully analyzed sealed tubes of standard sea water supplied by the 

 Copenhagen Laboratory as a necessary part of the outfit. The apparatus is 

 designed and constructed with the object of attaining maximum accuracy in 

 titration. Special precautions observed in titration are precise measurement 

 of the sample in an automatic pipette, vigorous stirring of the liquid by means 

 of a glass rod flattened at the end, and observation of exactly similar tints as 

 end points. 



DIPPING REFRACTOMETER METHOD 



Figure 4 shows the Bausch & Lomb dipping ref ractometer, together 

 with the heating trough and some of the glass cups (test tubes) into 

 which the samples of liquid to be tested are placed. The dipping 

 refractometer affords a convenient means of determining the salinity 

 of sea water with fair precision, and it can be used satisfactorily on 

 board ship in very rough weather. The instrument is designed to 

 measure the refractive indices of liquids at known temperatures but 

 must be used in connection with calibration charts, since it gives 

 indications directly only in terms of an arbitrary scale. 



Looking into the telescope of the instrument the observer sees part 

 of the field illuminated and part dark, with the dark and illuminated 

 parts quite sharply separated along a chord in the focal plane of the 

 objective. In the focal plane of the objective is mounted also a scale 

 graduated from to 100. By means of a micrometer screw the 

 observer can measure to four significant figures the position on the 

 scale of the chord of separation. 



The Coast and Geodetic Survey has purchased one of these instru- 

 ments, and a careful preliminary calibration has been made, both for 

 sea water and for boiler water. This preliminary calibration was 

 carried out in July, 1927, as follows : 



A quantity of sea water of average composition was taken from 

 the Atlantic Ocean off Beaufort, N. C, and divided into four por- 

 tions ; the first portion was left as it came and was of salinity 33.90 ; 

 the second was partially evaporated to salinity 40.22; the third was 

 diluted to salinity 31.25; the fourth was diluted to salinity 5.34. 

 These four samples were standardized by the Food, Drugs, and In- 

 secticides Administration, both by chemical titration for chlorine 

 content and by pycnometer for density. 



Each of the four samples and a sample of distilled water was run 

 several times with the refractometer from 3° to 26° C. The results 



