CHLORIDE 201 



Powdered Silver Chromate. Add slowly 200 ml. 5.5% potassium 

 chromate to 100 ml. boiling 10% silver nitrate soln. Add drops of 

 the chromate soln. until a slight excess is present as indicated by a 

 yellow color. Cool, wash the precipitate with water, and air-dry 

 on a Buchner funnel. 



Diphenylcarbazide Reagent. Dissolve 0.5 g. syw-diphenylcarba- 

 zide {Eastman Kodak Co.) in 70 ml. 95% alcohol; add 25 ml. 

 glacial acetic acid, and make up to 100 ml. with distilled water. 

 This reagent is stable at 20° for only 3 hr. 



PROCEDURE 



1. Since it will be necessary to measure columns of liquid longer 

 than the diameter of the optical field of the microscope, mount a 15 

 cm. steel rule, graduated in 0.5 mm., on the microscope stage. 



2. Fill a 10-12 cm. capillary tube (0.35 mm. inside diameter) to 

 nearly half its length with water from the water manipulator, and 

 adjust the tube so that its open end is in the optical field over the 

 zero mark of the stage micrometer and adjacent to the zero of the 

 steel rule. 



3. Introduce a 2-3 mm. column of zinc sulfate-sodium hydroxide 

 supernatant (page 200) or other fluid to be analyzed and measure its 

 length accurately, then introduce just nine times as much distilled 

 water. If the concentration of the unknown corresponds to less than 

 0.1% sodium chloride, less water will be required; if higher than 

 0.7%, more water must be used. 



4. Draw the liquid in 2 cm. from the open end, break off the 

 portion of the tube containing the added liquids, seal the ends in a 

 flame, and mix well by eight brief centrifugations, reversing the tube 

 after each one. 



5. Seal one end of a larger capillary tube (0.6 mm. inside diam- 

 eter), place a few grains of dry silver chromate in it and tap the 

 tube to get the material down to the closed end. Take care that none 

 of the substance is left near the open end; cut off a little of the tube 

 if necessary. 



6. Cut off the end of the first (smaller) tube above the column 

 of liquid, insert the open end into the silver chromate tube so that it 

 projects into it for about 1 cm. and fasten the two tubes together 

 with a ring of DeKhotinsky cement. 



7. Centrifuge with the larger tube down for a moment so that 



