be discarded; then, the silver nitrate storage 

 bottle, the beaker, the flask and the stirring bar 

 must be cleaned thoroughly before repeating 

 step 1. 



Step 3. After the silver nitrate is in solution, 

 pour the contents of the beaker into the silver 

 nitrate storage bottle. To insure that all silver 

 nitrate is remo\'ed from the beaker, rinse it 

 several times with water from the flask, and 

 pour the rinse water into the silver nitrate 

 bottle. Then, pour the remaining water from the 

 flask into the bottle. Next, fill the volumetric 

 flask with distilled water, empty it into the silver 

 nitrate bottle; refill and empty a second time; 

 finally fill a 1 -liter volumetric flask with dis- 

 tilled water, and empty it into the silver nitrate 

 bottle to make 7 liters of solution. Shake the 

 silver nitrate bottle vigorously for at least 5 

 minutes and return it to its place in the ap- 

 paratus. After handling the equipment and 

 chemical, wash hands thoroughly with salt 

 water and rinse with fresh water. 



I-ll Standardization of Silver Nitrate So- 

 lution. — After the silver nitrate solution is pre- 

 pared, it must be standardized to determine its 

 exact concentration in parts per thousand (%c). 

 Standardization is the process of determining 

 the difference between the concentration of the 

 silver nitrate solution (A) and the chlorinity 

 of the standard sea water (N). The difference 

 is called alpha (a). To standardize a silver 

 nitrate solution, titrate a standard sea water 

 sample three times at the beginning of the 

 analysis. Standardization also is performed fol- 

 lowing the duplicate titration of approximately 

 24 water samples or at the end of each station. 



1-12 Titration of a Sea Water Sample. — 



Titration of a sea water sample (either standard 

 sea water or an unknown sea water sample) in- 

 volves the following operations: 



( 1 ) Drawing the Sample with the Automatic 

 Pipette. — Drawing the sample for analysis, 

 whether it is standard sea water or an unknown 

 sea water sample, is carried out in precisely the 

 same manner. Before titration commences, all 

 solutions, samples, and apparatus must have 

 remained in the laboratory long enough to have 

 come to the same temperature. This usually re- 

 quires 6 to 12 hours. 



Step 1. Record the sample bottle serial num- 

 ber and sample bottle number on the D-Sheet in 

 the appropriate columns. If the sample is stand- 

 ard sea water, enter the chlorinity of the stand- 

 ard (N) in the Standardization column. 



Step 2. Turn on the salt water tap to which 

 the aspirator is attached, wipe the pipette 

 delivery tube with a clean paper tissue, insert 

 the tip of the pipette into the sample bottle, and 

 turn the stopcock to the fill position (fig. 1-5). 

 Partially fill the pipette and remove the sample 



Figure 1-5. Drawing the sample with the automatic 

 pipette. 



bottle to allow thorough rinsing by the suction 

 applied. Turn the stopcock to the vent position, 

 and drain the sample water into a beaker. Dis- 

 card this water. 



Step 3. Repeat Step 2. 



Step 4. Turn the stopcock to the fill position, 

 draw 15-ml. from the sample bottle, turn stop- 

 cock to off position and wipe the pipette delivery 

 tube with a paper tissue after withdrawing the 

 bottle. 



1-5 



