19.395 19.42 



025 



— .025 (average) 

 In the event the standardization reveals that 

 the solution is not within the limits of Knud- 

 sen's tables, then the solution must be ad- 

 justed. This adjustment is made by adding 

 more silver nitrate crystals if the solution is 

 too weak, i. e., shows a negative alpha lower 

 than —0.150, or by adding distilled water if 

 too strong, i. e., shows a positive alpha of more 

 than 0.145. 



To assist in making these adjustments, two 

 linear graphs are shown in figures 13-5 and 

 13-6. The first graph shows the number of 

 grams of silver nitrate to be added to each liter 

 of solution when the titration reveals a negative 

 alpha value below the limit given in the Knud- 

 sen tables The second graph shows the 

 number of milliliters of distilled water to be 

 added to each liter of solution when the titra- 

 tion reveals a positive alpha value greater than 

 the limit given in the Knudsen tables 

 Following are examples of both cases: 



1. Weak solution with negative alpha. As- 

 sume that from the standardization the alpha 

 is —0.199. Entering the graph in figure 13-5 

 with this value it is found that 0.380 gram of 

 silver nitrate per liter of solution must be 

 added. Looking at the graduations on the 

 black-painted silver nitrate solution bottle it 

 is seen that there are about 11.0 liters of solu- 

 tion. Therefore: 11.0 liters times 0.380 gram 

 gives a total of 4.18 grams of AgNOs that must 

 be added to the solution (110X0.380=4. 18). 

 Dissolve this silver nitrate in a few ml., say 50, 

 of distilled water, add it to the bottle and 

 shake the solution thoroughly before repeating 

 the standardization. 



2. Strong solution with positive alpha. As- 

 sume that from the standardization the alpha 

 is 0.186. Entering the graph in figure 13-6 

 with this value it is found that 9.4 ml. of dis- 

 tilled water must be added per liter of solution. 

 It is found that there are 12.5 liters of solution. 

 Therefore, 12.5 1X9.4 ml.=117.5 ml. of dis- 

 tilled water that must be added to the silver 

 nitrate solution. Shake the solution thor- 

 oughly before repeating the standardization. 



13-31 Calculations for Chlorinity and Sa- 

 linity. — It is essential that all standardizations 

 and titrations of sea water samples be duly 

 noted on a log sheet. Complete instructions 

 for this are given in chapter 14. The log sheet 

 used on U. S. Navy oceanographic surveys is 

 oceanographic log sheet D (PRNC-NHO- 

 1191). After the standardizations and titra- 

 tions of the sea water samples have been made 



H. O. 607 



and the results recorded on the log sheet, first 

 compute the average burette readings for each 

 sample. The next step is to determine the 

 correction k which must be applied algebrai- 

 cally to the average burette reading to obtain 

 the chlorinity. This has been greatly simpli- 

 fied by the use of Knudsen 's tables. Using the 

 alpha determined by the standardization, 

 enter Knudsen's tables; pages 23 through 34. 

 Alpha is shown at the top of the tables. Under 

 the given alpha (make sure that the sign + 

 or — is correct) find the two figures between 

 which each average burette reading lies. The 

 correction k is given in the right-hand column 

 with its proper sign. Determine k for each 

 average burette reading and apply k alge- 

 braically to obtain the chlorinity. 

 Example: (k from Knudsen's tables) 

 Alpha is + 0.025 



Average burette reading is 19.81 



Correction k (p. 30) is +.01 



Chlorinity °/oo is 19. 82 



Example: 



Alpha is + 0.025 



Average burette reading is 19. 72 



Correction k (p. 30) is +. 02 



Chlorinity 7oo is - -- 19.74 



If the average burette reading is the same as 

 one in the alpha column of the tables then 

 select the nearest even k. 



Once the chlorinity has been determined, 

 salinity in parts per thousand can be calculated 

 by the formula: 



S°/oo=0.03+1.805 (C17oo)- 

 A simpler and quicker method is by direct 

 inspection of table 1 6 in part II, or by Knudsen's 

 tables, pages 1 through 22. Enter either table 

 directly with the chlorinity and obtain the 

 salinity from the adjacent column on the right. 

 13-32 How To Secure (he Apparatus After 

 Completing the Titrations. — After the analyses 

 of a station have been completed, or a day's 

 work has been finished, the apparatus must be 

 secured. The pipette and burette will last 

 longer between cleanings if whenever they are 

 not in use they are kept filled. Fill the pipette 

 with sea water and the burette with silver 

 nitrate, and check to see there are no air 

 bubbles. Set the upper leveling stopcock of 

 the burette to the overflow position. This 

 will allow expansion of solution in the burette 

 in the event of temperature change. Apply a 

 pinchclamp to the tubing from the silver nitrate 

 bottle. Place an empty beaker below the 

 delivery stopcock of the burette to catch any 

 leakage. Clean the table with sea water, and 



127 



