containing standard sea water. Discard the re- 

 maining standard water and rinse the bottle 

 as described above. 



1-3 Salinity Determination by the Knudsen 

 Method. — Prof. Otto Pettersson introduced the 

 titration of chloride method for measuring the 

 salinity of sea water. Refinements were made by 

 Prof. Martin Knudsen and the present method 

 was named after him. This method is used ex- 

 tensively both in this oountiy and abroad, 

 ashore and at sea. Chlorinity is determined by 

 titrating a sample of sea water with a solution 

 of silver nitrate, the strength of which has been 

 determined against a known sample — ^standard 

 sea water. 



A general explanation of the titration of 

 chloride chemical reaction follows: (1) ^Vlien 

 silver nitrate is added to sea wat«r, white flakes 

 of silver chloride are precipitated according to 

 the general equation : 



AgNOa + NaCl^AgCU -fNaNOa 



(2) One ml. of phenosafranin solution is added 

 to the sea water as an indicator. (3) When all 

 the chloride in the sea water sample is precipi- 

 tated, a slight excess of silver nitrate gives, 

 in the presence of the phenosafranin, a blue 

 precipitate which indicates the titration is 

 comjDleted. 



1-4 Chemicals Required. — The following 

 chemicals are required for salinity titrations. 

 The amounts m parentheses are those required 

 to analyze 10 stations of 24 bottles each. 



Silver nitrate, crystals, C.P. (259.8 grams per 



jar — three jars) . 

 Phenosafranin, indicator (500 ml. bottle) .J 

 Standard sea water, Copenhagen, Eau de Mer 

 Normals (one vial per station to be ana- 

 lyzed). 



1-5 Apparatus Required. — In addition to the 

 apparatus previously listed in chapter H, the 

 following apparatus is required to cany out 

 salinity titrations by the luiudsen method : 

 Bottle, dropping, capacity : 125 ml. 

 Bottle or carboy (glass or polyethylene), 

 wide-mouth, with tubulature, capacity: 2 

 gal. 

 Bottle, glass*, narrow-mouth, S.T. ground 



flat glass stopper, capacity : 1 liter. 

 Bulb, pressure, rubber. 

 Burette, Knudsen, automatic-zeroing, range : 



12-18, 16-22, and 17-23 double ml. 

 Pipette, automatic-zeroing, acid, glass*, ca- 

 pacity: 15 ml. (or Knudsen pipette). 



1-6 Tables and Log Sheet Required.^Knud- 



sen's Hydrographical Tables of 1901 and Ocean- 



tPhenosafranin indicator usuaUy is prepared in tlie labora- 

 tory ashore. See paragraph 1-9. 



•Heat resistant borosilicate glass Is preferred. 



ographic Log Sheet-D, PRNC-NAVOCEANO 

 3167/4 (Rev. 4-63) (fig. 1-2), are required for 

 recording and computing salinity titration re- 

 sults. Knudsen's tables are used to convert 

 chlorinity to salinity and to correct for varia- 

 tions in the preparation of the titration solu- 

 tion. The Log Sheet-D is used to record the 

 titration steps and results in logical sequence. 

 Instructions for completing tlie entries on the 

 D-Sheet will be explained as the steps are per- 

 fonned. Make entries in pencil. This is a per- 

 manent record. Vessel, cruise, station, and serial 

 number are obtained from the Oceanographic 

 Log Sheet^A. 



1-7 The Automatic Pipette and Knudsen 

 Automatic Burette. — The titrations are car- 

 ried out using the automatic-zeroing pipette 

 (fig. 1-3) and the special Knudsen burette (fig. 

 1-4) . The pipette is calibrated to deliver almost 

 exactly 15 ml. of sample water. At the top is 

 a three-way stopcock for suction filling, off, and 

 delivery. Although the pipette is built to 

 deliver 15 ml., each one differs very slightly; 

 therefore, it is important that the same pipette 

 be used throughout a complete set of titrations. 

 The Knudsen burette is a very delicate piece 

 of glassware with a two-way filling stopcock 

 at the base, a three-way stopcock similar to that 

 of the pipette at the top, and a two-way delivery 

 stopcock below the graduations. It differs from 

 the ordinary burette in that it is calibrated in 

 double milliliters. A drainage value of 20.00 

 on the burette is equal to 40.00 milliliters of 

 solution. The double milliliter graduations per- 

 mit the use of a larger amount of less concen- 

 trated solution which increases the accuracy of 

 titrations. 



1-8 Setting Up the Titration Apparatus.— 



Before the pipette and burette are set up they 

 must be meticulously cleaned and the stopcocks 

 must be lubricated. Figures 1-3 and I^ show 

 schematic diagrams for arrangement of the 

 pipette and the Knudsen burette. 



Step 1. Make the light-proof, silver nitrate 

 solution storage bottle by painting the outside 

 of a 2-gallon, wide-mouth bottle or carboy with 

 several coats of black paint. Leave unpainted 

 a half-inch vertical strip up one side of the 

 bottle through which the solution may be seen. 

 Graduate the strip by liters with white paint. 

 Clean the inside thoroughly with soap and 

 water. Rinse with tap water. Finally, rinse 

 three times with distilled water before using. 



Step 2. Clamp the pipette, burette, and flasks 

 to support bars which are attached rigidly to 

 the titration table. Attach a filter pump, or 

 aspirator, to the salt water tap and connect it 

 with tygon tubing through the trap flask to 

 the pipette. Connect a piece of tygon tubing to 

 the overflow valve of the burette and terminate 



1-2 



