CHAPTER I 



SALINITY DETERMINATION OF SEA WATER SAMPLES 



I-l General. — As explained in previous chap- 

 ters, the most common method of obtaining sea 

 water samples is by means of the Nansen bottle, 

 and the water sample most frequently obtained 

 is a salinity sample. For this reason, it is very 

 important that the oceanographer develop skill 

 in perfonning salinity detenninations. 



Tlie salinity of a water sample can be deter- 

 mined by several methods, e.g., chemical titra- 

 tion, electrical conductivity, specific gravity, 

 and index of refraction. At the U.S. Naval 

 Oceanographic Office, the electrical conductivity 

 method is used for analyzing most salinity 

 samples; nevertheless, since the Knudsen titra- 

 tion method is desirable for laboratories witli a 

 sporadic incidence of salinity samples to ana- 

 lyze, the Knudsen method also is described. To 

 perform analysis by the Knudsen titration and 

 the electrical conductivity methods, a known 

 standard water sample is required. This known 

 sample, or standard, is "standard sea water." 



1-2 Standard Sea Water. — To insure world- 

 wide uniformity in chlorinity and salinity deter- 

 minations, the International Council for the 

 Exploration of the Sea jirepared a universal 

 reference, Eaih de Mer Nornuile, under the di- 

 rection of Professor Martin Knudsen in 1902. 

 A new standard, prepared in 1937 and having a 

 clilorinity of approximately 19.381 parts per 

 thousand, is used to determine the chlorinites of 

 all batches of standard sea water. Standard sea 

 water is the basis for all chlorinity titrations and 

 is tlie standard used to establish the concentra- 

 tion of the silver nitrate solution before and 

 during a series of titrations. Its chlorinity has 

 been determined with great accuracy, and it is 

 produced only by the International Association 

 d'Oceanographie, Physique (I.A.P.O.), Depot 

 d'Eau Normale, Charlottenlund Slot, Denmark. 

 Standard sea water is flame-sealed in glass vials 

 containing about 200 ml. of water. The chlo- 

 rinity, determined to three decimal places, is 

 given on the label of each vial ( fig. I-l ) . 



The standard sea water to be used sliould be 

 transferred from the vial into a sea water sam- 

 ple bottle. The bottle should be an old one, or 

 one that is well leached, be absolutely clean and 

 dry, and be provided with a good rubber gasket. 

 To transfer the standard sea water to the bottle 

 proceed as follows : 



Figure I-l. 



A vial of standard sea water and sea 

 water sample bottle. 



Step 1. With a small file, scratch a small nick 

 in the tapered tip of one neck of the standard 

 sea water vial, and with a sharp rap of the file 

 knock off the tip end of the neck. 



Step 2. Shake about 20 ml. of the standard 

 sea water into the prepared sample bottle. 

 Stopper the bottle and shake it vigorously. Pour 

 the rinse water out over the stopper. Repeat the 

 rinsing operation once more. 



Step 3. Next, scratch a nick on the closed 

 end of the vial and insert the open end into the 

 bottle. Give the scratched tip a sharp rap to 

 break it off, and drain the standard sea water 

 into the bottle. Stopper the sample bottle at 

 once to prevent evaporation. 



Step 4. Label the bottle, indicating the chlo- 

 rinity of the vial just emptied and the date. 



When a new vial of standard sea water is 

 opened, do not pour it into a bottle already 



I-l 



