- MEASUREMENT OF SALINITY OF SEA WATER 9 



connections, because the solution need not be kept for long periods. It migbt 

 be well to keep a large portion of a given sample of sea water and determine 

 its salinity at intervals with the apparatus. If the nitrate solution deteriorates, 

 there willbe an apparent increase in the salinity of the sample. The chemical 

 titration outfit here proposed may undergo many improvements. For example, 

 it may be found advantageous to use a Squibbs's automatic burette, which could 

 be connected to the aspirator bottle in such a way that the solution would not 

 come into contact with anything except glass. In the meantime, while rubber 

 connections are used, they should be renewed whenever the rubber ceases to 

 be pliable. 



The potassium chromate solution must be made up with chemically 

 pure chromate and good distilled water. Its concentration need not 

 be precise, however, and it may be made up by a pharmaci,st or other 

 competent person, as follows: Dissolve 5 grams of chemically pure 

 potassium chromate crystals in less than 100 c. c. of distilled water. 

 Add silver nitrate solution slowly until a blood-red precipitate is 

 formed that does not disappear upon .stirring. Filter and add 

 enough distilled water to the filtrate to make 100 c. c. of solution. 

 This solution should be kept in tincture bottle K. 



The outfit should now be ready for use. The procedure for deter- 

 mining the salinity of a given sample of sea water is as follows : 



1. Place some of the sample in the beaker that is toward the 

 front of the case. Rinse the evaporating di,sh, 10 c. c. pipette, and 

 stirring rod with some of the sample and then shake them clear of 

 rinsing water. 



2. Pump up a little pressure in the aspirator bottle and loosen the 

 rubber stopper at the top of the burette. Fill the burette with 

 silver nitrate solution, controlling the flow by means of the left-hand 

 pinchcock until the zero mark on the burette is precisely tangent to 

 the bottom of the meniscus of the nitrate solution. 



3. U,sing the 10 c. c. pipette, measure out 10 c. c. of sea-water sample 

 into the evaporating dish. Using the 1 c. c. pipette, add about % 

 c. c. of potassium chromate solution. 



4. Allow silver nitrate solution to run down into the evaporating 

 dish from the burette, stirring constantly, until a red tint appears 

 that does not disappear upon stirring. The reading of the burette 

 at the bottom of the meniscus will then be the salinity of the sample 

 in parts per thousand (by weight) ,of total dissolved solids. 



The solution should be stirred vigorously near the " end point " to 

 coagulate the white precipitate of silver chloride and soak out the 

 sodium chloride. 



The observer can usually estimate a minimum value for the salinity 

 and let the nitrate .solution run out of the burette rapidly down to 

 the mark on the burette corresponding to the estimated minimum 

 salinity. After that he should let the nitrate drip down drop by 

 drop. Possibly one or more drops will come down after the color 



