Apparatus— The apparatus (see illustration)consists of a 50-mLflask with a side arm connected to a source of carbon dioxide humidified by bubbling through a saturated solution of sodium bicarbonate and equipped with a top-mounted stopper fitted with an exit tube connected via a T-tube to a system vent and a leveling buret and reservoir.

Reagents—

Procedure— Add 25mLof Saturated sodium bicarbonate solutionto the 50-mLflask,and flush the system by allowing humidified carbon dioxide to enter through the side arm.Close the carbon dioxide inlet and the system vent,and stir the Saturated sodium bicarbonate solutionuntil no further carbon dioxide absorption is noted from successive buret readings.Maintain atmospheric pressure in the apparatus by adjusting the Displacement solutionto the same level in both the reservoir and the buret,noting the buret reading.Open the system vent,and reintroduce humidified carbon dioxide through the side arm of the flask.Close the carbon dioxide inlet and the system vent,and stir the Saturated sodium bicarbonate solutionvigorously until no further carbon dioxide absorption is noted.Repeat the carbon dioxide absorption procedure starting with “Open the system vent”until no more than a 0.2-mLchange in buret reading is noted.Discontinue stirring,reintroduce humidified carbon dioxide through the side arm of the flask,remove the top-mounted stopper from the flask briefly,and promptly add about 10g of Sodium Bicarbonate,accurately weighed,to the flask.Replace the stopper,continue the flow of humidified carbon dioxide for about 30seconds,and then close the carbon dioxide inlet and the system vent.Stir the solution in the flask vigorously until carbon dioxide absorption ceases,noting the volume absorbed from the buret reading.Restore atmospheric pressure in the apparatus by leveling the Displacement solution in the reservoir and the buret,and discontinue stirring.Open the system vent,and flush humidified carbon dioxide through the system.Close the carbon dioxide inlet and the system vent,and stir the solution in the flask vigorously until carbon dioxide absorption ceases.Determine the total volume,V,in mL,of carbon dioxide absorbed after the addition of the specimen to the flask,and calculate the percentage of carbonate in the portion of specimen tested by the formula: in which Pis the ambient atmospheric pressure,in mm of mercury,Tis the ambient temperature,and Wis the quantity,in g,of specimen taken.[NOTE—Maintain a constant temperature during the measurement of the volume of carbon dioxide absorbed.]The limit of carbonate is not more than 0.23%.

Potassium chloride solution— Dissolve 10g of potassium chloride in 1000mLof 0.36Nhydrochloric acid.

Calcium standard preparations— Transfer 249.7mg of calcium carbonate,previously dried at 300for 3hours and cooled in a desiccator for 2hours,to a 100-mLvolumetric flask.Dissolve in 6mLof 6Nhydrochloric acid,add 1g of potassium chloride,dilute with water to volume,and mix.Transfer 10.0mLof this solution to a second 100-mLvolumetric flask,dilute with Potassium chloride solutionto volume,and mix.This solution contains 100µg of Ca per mL.Transfer 2.0-,3.0-,4.0-,and 5.0-mLportions of this solution to separate 100-mLvolumetric flasks (each containing 6mLof 6Nhydrochloric acid),dilute with Potassium chloride solutionto volume,and mix.These Calcium standard preparationscontain 2.0,3.0,4.0,and 5.0µg of Ca per mL,respectively.

Magnesium standard preparations— Place 1.000g of magnesium in a 250-mLbeaker containing 20mLof water,and carefully add 20mLof hydrochloric acid,warming if necessary to complete the reaction.Transfer this solution to a 1000-mLvolumetric flask containing 10g of potassium chloride,dilute with water to volume,and mix.Transfer 10.0mLof this solution to a 100-mLvolumetric flask containing 1g of potassium chloride,dilute with water to volume,and mix.Transfer 10.0mLof this solution to a second 100-mLvolumetric flask,dilute with Potassium chloride solutionto volume,and mix.This solution contains 10.0µg of Mg per mL.Transfer 2.0-,3.0-,4.0-,and 5.0-mLportions of this solution to separate 100-mLvolumetric flasks (each containing 6mLof 6Nhydrochloric acid),dilute with Potassium chloride solutionto volume,and mix.These Magnesium standard preparationscontain 0.2,0.3,0.4,and 0.5µg of Mg per mL,respectively.

Test preparation— Transfer 3.0g of Sodium Bicarbonate to a 100-mLvolumetric flask,add 6mLof 6Nhydrochloric acid and 1g of potassium chloride,dilute with water to volume,and mix.

Procedure for calcium— Concomitantly determine the absorbances of the Calcium standard preparationsand the Test preparationat the calcium emission line at 422.7nm with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering á851ñ)equipped with a calcium hollow-cathode lamp and a nitrous oxide–acetylene flame,using Potassium chloride solutionas the blank.Plot the absorbances of the Calcium standard preparationsversus their contents of calcium,in µg per mL,by drawing a straight line best fitting the four plotted points.From the graph so obtained determine the quantity,in µg,of Ca in each mLof the Test preparation.Calculate the percentage of Ca in the specimen taken by dividing this value by 300:the limit is 0.01%.

Procedure for magnesium— Concomitantly determine the absorbances of the Magnesium standard preparationsand the Test preparationat the magnesium emission line at 285.2nm with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering á851ñ)equipped with a magnesium hollow-cathode lamp and a reducing air–acetylene flame,using Potassium chloride solutionas the blank.Plot the absorbances of the Magnesium standard preparationsversus their contents of magnesium,in µg per mL,by drawing a straight line best fitting the four plotted points.From the graph so obtained determine the quantity,in µg,of Mg in each mLof the Test preparation.Calculate the percentage of Mg in the specimen taken by dividing this value by 300:the limit is 0.004%.

Nitric acid diluent— Dilute 40mLof nitric acid to 1000mLwith water.

Standard preparation— Transfer 1.000g of copper to a 1000-mLvolumetric flask,dissolve in 20mLof nitric acid,dilute with 0.2Nnitric acid to volume,and mix.Transfer 10.0mLof this solution to a second 1000-mLvolumetric flask,dilute with 0.2Nnitric acid to volume,and mix.This solution contains 10.0µg of copper per mL.Store in a polyethylene bottle.

Test preparation— Transfer 5.0g of Sodium Bicarbonate to a 100-mLplastic volumetric flask,and carefully add 4mLof nitric acid.Sonicate for 30minutes,dilute with water to volume,and mix.

Procedure— To 10.0mLof the Test preparationadd 20µLof Standard preparation,and mix.This Spiked test preparationcontains 0.02µg of added Cu per mL.Concomitantly determine the absorbances of the Test preparationand the Spiked test preparationat the copper emission line at 324.7nm with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering á851ñ)equipped with a copper hollow-cathode lamp and a flameless electrically heated furnace,using Nitric acid diluentas the blank.Plot the absorbances of the Test preparationand the Spiked test preparationversus their contents of added Cu,in µg per mL,draw a line connecting the two points,and extrapolate the line until it intercepts the concentration axis.From the intercept determine the quantity,in µg,of Cu in each mLof the Test preparation.Calculate the quantity of Cu in the specimen tested by multiplying this value by 20:the limit is 1µg per g.

Silver sulfate solution— Dissolve 22g of silver sulfate in 2000mLof sulfuric acid.

Indicator solution— Dissolve 1.485g of 1,10-phenanthroline and 695mg of ferrous sulfate in water to make 100mLof solution.

Standard preparation— Transfer 850.3mg of potassium biphthalate,previously crushed lightly and dried at 120for 2hours,to a 1000-mLvolumetric flask,dilute with water to volume,and mix.Transfer 6.0mLof this solution to a 100-mLvolumetric flask,dilute with water to volume,and mix.This solution contains the equivalent of 0.06mg of organics equivalents per mL.Transfer 40.0mLof this solution to a 500-mLreflux flask.

Test preparation— Transfer about 20g of Sodium Bicarbonate,accurately weighed,to a 500-mLreflux flask.Add 20mLof water,and swirl.Cautiously add 20mLof sulfuric acid,and swirl.[Caution—Perform this operation under a hood ].

Blank— Add 40mLof water to a 500-mLreflux flask.

Procedure— Concomitantly treat the Standard preparation,the Test preparation,and the Blankas follows.Add 1g of mercuric sulfate and about 5glass beads.Cool the flask in an ice bath,and add 5mLof Silver sulfate solution.While gently swirling the flask in the ice bath,add 25.0mLof 0.025Npotassium dichromate VSand,slowly,70mLof Silver sulfate solution.Fit a cold water condenser on the reflux flask,and reflux for 2hours.Allow the contents of the flask to cool for 10minutes,and wash the condenser with 50mLof water,collecting the washings in the flask.Add water to the flask to obtain a volume of about 350mL.Add 3drops of Indicator solution,and titrate,at room temperature,with 0.07Nferrous ammonium sulfate VSuntil the solution changes from greenish blue to reddish brown.Calculate the amount,in mg,of organics equivalent in the Standard preparationtaken by the formula: in which Nis the normality of the ferrous ammonium sulfate VS;and VBand VSare the volumes,in mL,of 0.07Nferrous ammonium sulfate VSconsumed by the Blankand the Standard preparation,respectively.In a suitable system,between 2.328and 2.424mg is found.Calculate the amount,in mg,of organics equivalent in the portion of Sodium Bicarbonate taken by the formula: in which VUis the volume,in mL,of 0.07Nferrous ammonium sulfate VSconsumed by the Test preparation:the limit is 0.01%.