sample into the waste jar. Once the titrations 

 are started, however, it is not necessary to 

 reclean the beaker after each titration unless 

 the titration has run over the end point. 

 With a proper end point the silver chloride 

 remaining stuck to tha sides of the beaker after 

 the sample has been poured out should be 

 chemically neutral and the beaker may be 

 reused for the next sample as is. 



When the end point had been exceeded, 1 

 or 2 methods must be followed before the 

 beaker can be used for further titrations. One 

 method is to add a drop or two of sea water to 

 the sample — enough to again turn the sample 

 to pale yellow. Then continue the titration to 

 the end point to neutralize the solution. Do 

 not take a burette reading for this. The sample 

 may then be discarded. The second method 

 and the one to use in the event the exceeded 

 end-point sample has been discarded before 

 carrying out the above method, is to wash the 

 beaker with tap water, rinse with distilled 

 water, and dry thoroughly before again using 

 it for titrations. 



When running sea water sample titrations a 

 minimum of two titrations of each sample must 

 be made. The burette readings of each titra- 

 tion must be within 0.02 to be acceptable. 

 Whenever the readings have a difference greater 

 than 0.02, a third or, if necessary, more titration 

 must be run until 2 readings are obtained 

 within the prescribed limits. When making 

 the initial standard sea water titrations, a 

 minimum of 3 titrations must be made for each 

 station. Single standard sea water titrations, 

 if they agree with the original, are made for 

 every sixth sea water sample. 



A summary of important points to be re- 

 membered when drawing and titrating follows: 



1. Always keep the equipment spotlessly 

 clean. 



2. Always shake the silver nitrate solution 

 bottle thoroughly for 5 minutes before running 

 each station. 



3. Always rinse the pipette twice with water 

 to be analyzed before drawing the measured 

 sample. 



4. Be sure all solutions, samples and in- 

 struments are at the same temperature. 



5. Titrate all sea water samples and standard 

 sea water in an absolutely identical manner. 



6. Be sure each titration lasts the same length 

 of time. 



7. Have the color of each end point identical 

 for all samples. 



8. Read the burette immediately after the 

 end point has been reached. 



126 



9. Run at least 2 titrations for each sample 

 and be sure they are within 0.02 of each other. 



13-30 Standardization and Adjustment of 

 the Silver Nitrate Solution. — Before the titra- 

 tions of sea water samples are run to determine 

 chlorinity, the silver nitrate solution must be 

 standardized to learn its exact concentration in 

 parts per thousand (°/oo) ■ Also in order to carry 

 out the calculations required to determine 

 chlorinity, this concentration must fall within 

 — 0.150°/oo to 0.145°/oo of the chlorinity of 

 standard sea water. The latter is usually 

 about 19.380°/ooi the exact chlorinity always 

 being given on the label of each vial. It is 

 important to keep the silver nitrate concentra- 

 tion within the limits of the Hydrographical 

 tables, usually referred to as Knudsen's tables, 

 to find a correction value k necessary for the 

 calculations given below. 



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) which is exactly 

 known. The difference is called alpha (a). 

 Standardization is expressed by the following 

 formula: 



(N)-(A)=a. 

 For example: 



Chlorinity of standard sea (N) = 19. 395 



water. 

 Burette reading of titration. (A) = 19. 37 



also 



Alpha. 



(a) = +.025 



Chlorinity of standard sea (N) = 19. 395 



water. 

 Burette reading of titration. (A) = 19. 40 



Alpha (a) = -.005 



An average alpha is obtained from the three 

 best titrations of the standard sea water. This 

 average alpha is the value used to obtain the 

 correction k from Knudsen's tables, which in 

 turn is applied to the burette readings of the 

 sea water samples to obtain chlorinity. 

 For example: 



(N)- (A)= (a) 



19.395 19.38 0.015 



19. 395 19. 36 . 035 



19. 395 19. 37 . 025 



. 025 (average) 

 Or where alpha comes out negative: 



(N) 

 19. 395 

 19. 395 

 19. 395 



(A)= (a) 

 19.42 -0.025 

 19.42 - .025 

 19.47 - .075 



(poor run- 

 card) 



-dis- 



H. O. 607 



