full. This will insure that all silver nitrate is 

 removed from the jar. Stir with a glass rod 

 until the crystals are dissolved, then divide 

 the solution roughly equally between two 

 2,000-ml. volumetric flasks. Add distilled 

 water to each flask (pouring it from the same 

 beaker) up to the graduation mark; thea pour 

 each into the black silver nitrate bottle. Al- 

 low the flasks to drain well. The solution must 

 be colorless. If it is cloudy or turns whitish, 

 it is contaminated and must be discarded and 

 all glassware thoroughly cleaned before using 

 again. Refill both flasks to the graduation 

 marks with distilled water and a third time 

 with 1 flask until a total of 10 liters of solution 

 is made up. Shake the bottle vigorovfily for 

 at least 5 minutes before returning the bottle 

 to its rack. Shake the bottle vigorously for 

 5 minutes before each series, or da3''s work, of 

 titrations is started. Nerer start a series of 

 titrations without shaking the silver nitrate. 



If the silver nitrate is to be weighed out 

 directly for making up the solution first, place 

 a 800- or 1,000-ml. beaker on the triple beam 

 balance, weigh it carefully to the nearest 0.1 

 gram, then add 371.1 grams to the beaker 

 weight on the scale. Add silver nitrate crys- 

 tals until balance is again obtained. Now add 

 distilled water until the beaker is three-fourths 

 full and dissolve the crystals. Make up to 10 

 liters by adding distilled water as described 

 above. 



.Silver nitrate is a very poisonous compound, 

 both internally and externally. Upon weigh- 

 ing out this chemical on the balance, frequently 

 tiny crystals are spilled onto the laboratory 

 bench. Therefore, the bench should always 

 be wiped carefully with a cloth soaked in sea 

 water and then with one soaked in fresh water. 

 Anyone handling the equipment or chemical 

 should wash their hands thoroughly in salt 

 water and again in fresh water afterward. 



The adjustment of the silver nitrate solution 

 to bring its strength within the range of Knud- 

 sen's Hydrographical Tables of 1901 and in- 

 structions for the use of these tables are given 

 in section 13-30. 



13-27 Standard Sea Water.— To insure 

 worldwide uniformity in chlorinity and salinity 

 determinations, the International Council for 

 the Exploration of the Sea prepared a universal 

 reference, Eau de Mer Normale, under the 

 direction of Professor Martin Knudsen in 1902. 

 A new primary standard, prepared in 1937 and 

 having a chlorinity of 19.381 %o, is used to 

 determine the chlorinities of all batches of 

 standard sea water. Standard sea water is the 

 basis for all chlorinity titrations and is the 



H. O. 607 



standard used to establish the concentration 

 of the silver nitrate solution before and during 

 a series of titrations. Its chlorinity has been 

 determined with great exactness, and it is pro- 

 duced only by the Association d'Oceanographie 

 Physique, Depot d'Eau Normale, Charlotten- 

 lund, Danemark. It is put up in flame-sealed 

 glass vials containing about 200 ml. of water. 

 The chlorinity to three decimal places is given 

 on the label of each vial. Standard sea water 

 is expensive and so must be used conservatively. 



Before the standard sea water can be used, 

 it must be transferred to a sea water sample 

 bottle. The bottle should be an old one, or 

 one that is well-leached, and provided with a 

 good rubber gasket. The bottle must be 

 ahaolutely clean and dry. To transfer the 

 standard sea water to the bottle, scratch a 

 small nick in the tapered tip of one neck of the 

 vial and then, with a sharp rap of the glass-file, 

 knock off the tip end of the neck. Shake about 

 20 ml. of the standard sea water into the pre- 

 pared sample bottle. Stopper the bottle and 

 shake it vigorously. Pour this rinse water out 

 over the stopper. Repeat this rinsing operation 

 once more. Now scratch a nick on the closed 

 end and insert the open end into the bottle. 

 Give the scratched tip a sharp rap to break it 

 off and the standard sea water will drain freely 

 into the bottle. Stopper the sample bottle 

 at once to prevent evaporation. Do not open 

 the bottle except when actually drawing a 

 sample. Label the bottle, indicating the chlo- 

 rinity of the vial just emptied and the date. 



When a new vial must be opened, do not 

 pour it into a bottle already containing standard 

 sea water but take another water sample 

 bottle, thoroughly clean and dry it and fill as 

 described above. 



13-28 Drawing the Sample With the Auto- 

 matic 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. Unless otherwise directed, 

 this technique should never vary. Before 

 any titrations are started all solutions, samples, 

 and apparatus must have remained in the 

 laboratory long enough to have come to the 

 same temperature. This should be at least 6 

 hours and preferably 12. 



The 15-ml. Knudsen automatic pipette must 

 be rinsed twice with the sample water to be 

 analyzed before the measured sample is drawn. 

 To do this, turn on the salt water tap to which 

 the aspirator is attached, insert the tip of the 

 pipette into the sample bottle and turn the 

 stopcock to the fill position. Fill the pipette 

 and lower the sample bottle to allow thorough 



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