CALCIUM 275 



8. Run a control by titrating 50 jul. of the acid with the alkali to 

 the same end point. 



note: The precautions given on page 257 for the exclusion of atmospheric 

 carbon dioxide during the titration should be followed. It would also be 

 advantageous to substitute tetramethylammonium hydroxide for the 

 sodium hydroxide in order to avoid the difficulties occasioned by the use 

 of the latter in fine-bore microburettes; thymol blue will serve as a 

 better indicator than phenolphthalein (page 291). 



Lindner and Kirk Cerinietric Method for Calcium 



SPECIAL REAGENTS 



Water. Distill all water used for reagents or otherwise from an all- 

 glass apparatus, and likewise distill all sulfuric acid used. 



4% Ammonium Oxalate. Filter through fine asbestos on a sintered- 

 glass filter. 



Wash Solution. Saturate 10% (by vol.) ammonium hydroxide with 

 freshly precipitated and washed calcium oxalate. Filter through 

 asbestos on a sintered-glass filter. Prepare fresh from time to time 

 to avoid the formation on long standing of a very fine suspension 

 that cannot be properly filtered. 



Saturated Sodium Acetate. 



0.01 N Ceric Sulfate. 



0.01 N Ferrous Ammonium, Sulfate in 0.1 N Sulfuric Acid. Store in 

 a dark bottle under illuminating gas and withdraw portions as 

 needed. The soln. is stable in contact with air for 2 weeks or longer. 



0.0025 M Phenanthroline Ferrous Sulfate. Prepare from a stock 

 soln. of 0.025 AI which is made up by dissolving 1.485 g. o-phen- 

 anthroline in 100 ml. of 0.025 M ferrous sulfate. 



The advantage of using nitro-o-phenanthroline ferrous sulfate has been 

 emphasized by Salomon et al. (1946). A 0.05% soln. of lisamine green {Bntish 

 Drug House Ltd.) gives a smaller blank than the o-phenanthroline ferrous 

 sulfate, according to Nimmo-Smith (1946), who also recommends the latter 

 reagent because it is cheaper. 



0.1 N Hydrochloric Acid. 



6 N Sulfuric Acid. 



Asbestos. Treat all asbestos used as follows: Wash and ignite 

 Italian medium fiber asbestos, and grind in a mortar. Boil in acidi- 

 fied ceric sulfate soln. and wash well with water on a sintered 

 glass filter. Store a suspension of the material in water. 



