220 CUVETTE COLORIMETRY 



0.1 N Ceric Bisulfate (approx.). Dissolve 29 g. anhydrous eerie 

 bisulfate in 1 A^ sulfuric acid to make 500 ml. (The greater ease 

 of solution of the bisulfate makes it preferable to the sulfate. The 

 bisulfate is obtainable in about 92% purity from G. Frederick 

 Smith Chemical Co.) Store in amber bottles and protect from 

 light. 



In preference to ceric sulfate, Kochakian and Fox (1944) have stressed the 

 greater sharpness of the end point in titration with ammonium hexanitrato- 

 cerate using setopaHne C as the indicator. Prepare a 0.01 A^ soln. by dissolving 

 6 g. ammonium hexanitratocerate, reagent grade, in about 200 ml. 1 N per- 

 chloric acid and dilute to 1 I. with the acid. Do not heat during preparation, 

 and store in a black bottle in the dark. Prepare a 0.05% setopaline C soln. by 

 adding 50 mg. of the dye (Eimcr and Amend) to 100 ml. distilled water and 

 warming on a hot plate or bath. Precipitation occurs on cooling, therefore the 

 soln. must be warmed before use and used while warm. 



0.0035 N, 0.001 N, 0.0007 N, and 0.00035 N Ceric Bisulfate 

 (approx.). Prepare these solns. just when needed from the 0.1 

 N soln. Use 0.2 A^ sulfuric acid to dilute the 0.1 A'' to 0.0035 A^. 

 Use 0.1 N sulfuric acid for dilution to the weaker concentrations. 

 Prepare the 0.007 A^ and 0.00035 A^ solns. from the 0.0035 A^ soln. 

 Store in amber bottles and protect from light. 



Standard 0.1 N Sodium Oxalate. Dissolve 3.3498 g. sodium oxalate, 

 analytical reagent grade, in 52 ml. 1 A^ sulfuric acid and add water 

 to make 500 ml. Store in amber bottle; the soln. is stable for at 

 least 6 months. 



Standard 0.0005 N, 0.00025 N, and 0.0002 N Sodium Oxalate. Pre- 

 pare fresh when needed from the 0.1 A'' soln. by dilution with 

 water. 



0.5% and 1% Potassium Iodide (approx.) Prepare fresh for use 

 from analytical reagent grade of the salt. (When tested with 

 starch, no trace of free iodine should be present.) 



95% Ethyl Alcohol. Filter through two layers of ashless filter paper 

 on a Buchner funnel. 



2% and 1% Starch (Lintner Soluble). Prepare the 2% soln. in 

 saturated sodium chloride soln. every 2 weeks by making a paste, 

 diluting to vol. and boiling for 5-10 min. Prepare the 1% soln. 

 fresh for use from the 2% soln. by diluting with water. 



