A:Infrared Absorption á197Kñ: on the undried specimen.

B: When strongly heated,the salt chars,and on ignition leaves a more or less blackened residue having a yellow surface.The residue is soluble in warm nitric acid,and this solution,when dropped into a large excess of water,produces a white turbidity.

C: Dissolve 1g in ammonia TS.When treated with hydrogen sulfide in excess,a black precipitate is obtained.Filter this mixture,drive off the excess hydrogen sulfide by heating,and allow to cool.To a portion of this cooled solution add an excess of calcium hydroxide TS,and boil:a white precipitate is formed.Reserve a second portion of the cooled solution for the test for Limit of nitrate.

Standard solution— Prepare a solution containing 1000µg of copper per mL,a solution containing 1000µg of lead per mL,and a solution containing 1000µg of silver per mL.Transfer 3.0mLof each solution to a 2000-mLvolumetric flask,dilute with 1Nnitric acid to volume,and mix.[NOTE—The concentrations of copper,lead,and silver in this solution may be modified by using a different quantity or by further dilution to bring the absorption responses within the working range of the atomic absorption spectrophotometer.]

Test solution— Ignite about 3g of Bismuth Citrate,accurately weighed,in a porcelain crucible,cool,and cautiously add 6Nnitric acid to dissolve the residue.Add 100mLof water,and mix.Awhite precipitate forms.Filter this mixture,evaporate on a steam bath to obtain about 15mLof solution,and filter again.Dilute the filtrate with water to 20.0mL.

Procedure— Concomitantly determine the absorbances of the Standard solutionand the Test solutionat the emission lines of 324.7nm,217nm,and 328.1nm for copper,lead,and silver,respectively,with an atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering á851ñ)equipped with copper,lead,and silver hollow-cathode lamps and an oxidizing flame.The absorbances of the Test solutiondo not exceed those of the Standard solutionfor each element (10µg per g).

Standard solution— Transfer 242.0mg of bismuth nitrate pentahydrate to a 100-mLvolumetric flask.Add 3mLof 1.5Nnitric acid,swirl to dissolve,dilute with water to volume,and mix.Transfer 1.0mLof this solution to a 500-mLvolumetric flask,add 250mLof 1.5Nnitric acid,dilute with water to volume,and mix.This solution contains 2.0µg of bismuth (Bi)per mL.[NOTE—The concentration of bismuth in this solution may be modified by using a different quantity or by further dilution to bring the absorption responses within the working range of the atomic absorption spectrophotometer.]

Test solution— Prepare a mixture of 5.0g of Bismuth Citrate and 100mLof water,and stir by mechanical means the suspension thus obtained for 2hours.Pass through filter paper.Pass the filtrate thus obtained through a filter having a 0.1-µm or finer porosity.To 10.0mLof the filtrate add 0.1mLof nitric acid.

Procedure— Concomitantly determine the absorbances of the Standard solutionand the Test solutionat the emission line of 223.06nm for bismuth with an atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering á851ñ)equipped with a bismuth hollow-cathode lamp and an oxidizing flame.The absorbances of the Test solutiondo not exceed those of the Standard solution(40µg per g).