SODIUM 271 



Sodium may also be determined by difference using both the Lind- 

 erstr0m-Lang method for sodium plus potassium (page 266) and the 

 Norberg method for potassium alone (page 268). A colorimetric 

 method for sodium is given on page 203. 



Lindner and Kirk Method for Sodium 



SPECIAL REAGENTS 



Calcium Hydroxide. 



0.1 N Hydrochloric Acid. 



Zinc Uranyl Acetate Solution. Prepare as described on page 203 

 and let stand 24 hr. Filter through a sintered-glass bacteria-proof 

 filter. Should turbidity appear, refilter. 



Wash Solution. Saturate 95% alcohol with sodium zinc uranyl 

 acetate and filter absolutely clear as above. 



Asbestos. Grind washed and ignited Italian asbestos in a mortar 

 until fine. Boil in successive portions of eerie sulfate soln. acidi- 

 fied with sulfuric acid. Wash well with water and store in an all- 

 glass container. 



5% Sulfuric Acid. Prepare from acid redistilled in a glass ap- 

 paratus. 



0.01 N Ceric Sulfate Solution. Standardize against pure sodium 

 oxalate or potassium ferrocyanide. 



Indicator Solution. 0.0025 M phenanthroline ferrous sulfate or 

 0.1% setopaline C (see page 275). 



Standard Sodium Chlojide Solutions. 



Spirals of Cadmium. Cut a thin ribbon from a stick of the metal 

 with a lathe tool. Flatten the helix formed to a disc^having a total 

 surface of about 2 cm.^; leave one end extending upward to serve 

 as a handle. This reductor may be used almost indefinitely. 



Water. Redistill all water used from an all-glass apparatus. 



PROCEDURE 



1. Incinerate the sample at about 450° for several hr. in a small 

 platinum crucible. 



2. Add about 50 /nl. 0.1 A'' hydrochloric acid to the cooled clean 

 white ash. 



3. Transfer with washing by means of a large capillary pipette 

 to a centrifuge cone of about 0.2 ml. capacity. Add a little calcium 

 hydroxide with a toothpick and mix well to precipitate phosphate. 



