MEASUKEMENT OF SALINITY OF SEA WATEll 7 



The arrangement of the apparatus should be clear from the figure. 

 Glass tubing is cut by marking it with a three-cornered file, placing 

 the thumb-nails opposite the file mark and pulling the ends apart 

 with a slight inclination away from the scratch. Raw ends of glass 

 tubing should be " fire polished " by heating to redness in a blowtorch 

 flame. 



It will be found convenient to set the evaporating dish in a wooden 

 block mounted in a set of boat-compass gimbals. This has not been 

 done in the outfit shown in Figure 3. The parts of the apparatus, 

 all of which appear in the figure, are designated there as follows : 



A. — ^Aspirator bottle (for silver nitrate solution). 



B. — Rubber pressure bulb (for developing a slight air pressure in the aspirator 

 bottle). 



C. — Glass elbow tube. 



D. — Burette (should be fitted with plain rubber stopper at top). 



E. — Parts of burette attachment. 



F. — Evaporating dish (the wooden block shown may be mounted in boat- 

 compass gimbals ; if the locker is made of the height shown in the figure, there 

 will be plenty of room for this change). 



Gr. — Beaker (for supply of sea-water sample). 



H. — Stirring rod (not shown in the figure; should be where J is). 



J.-^Transfer pipette, 10 c. c, for measuring out sample of sea water (out of 

 place in the figure ; should be in position j ) . 



K. — Tincture bottle (for supply of potassium chromate indicator). 



L. — Transfer pipette, 1 c. c. (for adding potassium chromate, indicator to 

 measured portion of sea- water sample in the evaporating dish). 



M. — Volumetric flask, holding exactly 2 liters of solution to etched mark in 

 neck (for use in preparing silver niti-ate solution). 



y. — Extra beaker (for use in preparing silver nitrate solution). J 



P. — ^Wash bottle (to be kept filled with distilled water). 



Before the apparatus is assembled all tubing, stoppers, and con- 

 tainers should be carefully washed and then well rinsed with distilled 

 water. 



The silver nitrate solution must be precisely of the strength already 

 mentioned, 27.09 grams of silver nitrate per liter of solution — 54.18 

 grams for one filling of the volumetric flask. Enough silver nitrate 

 solution for 50 to 60 titrations can be prepared quite easily as follows : 



Making sure that the wash bottle and volumetric flask are clean, 

 fill the wash bottle and partly fill the volumetric flask with distilled 

 water so that the volumetric flask can still receive at least a beakerful 

 of solution below the mark in the neck. See that the beaker reserved 

 for silver nitrate is clean, rinse it with distilled water, and carefully 

 empty the weighed portion of silver-nitrate crystals into the bottom 

 of it, -- Using the wash bottle, carefully rinse the inside of the bottle 

 that held the crystals and pour all the rinse water into the beaker. 



Carefully wash down the inside of the sides of the beaker by means 

 of the wash bottle and get the crystals into solution with as little 

 agitation and as little water as possible. Pour the solution carefully 



