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a <br /> 14 6.3 Test RMedure. Pipette 10 al. of the dilute test solution (see <br /> 4.5,i) into a 250 al. beaker. Using red litmus as an indicator, add ammo- <br /> nium hydroxide until the last drop changes the litmus to blue. Then add to <br /> the solution 30 ml. of the buffer solution (4,5.6.1.1) and 15 to 20 drops of <br /> Eriochrame Black T indicator (4.5.6.1.2). Titrate with the standard ethyl-• <br /> enedipwine tetraacetate disodiuo solution (4.5.6.1.3) until the color dust <br /> chang,s from purple to grey. Calculate the percent zinc as follows: <br /> Percent zinc = (B)(Z)(100) <br /> Where: Z = zinc factor (see 4.5.6.2) <br /> B = ml, of ethylenediamine tetraacetate disodium <br /> solution used to reach the end point <br /> 4.5.7 Extraneous elements determination. Extraneous elements (see 3.3) <br /> shall `te deterr-ined as follows: <br /> 4.5,7.1 Arsenic determination. The arsenic content shall be determined <br /> using the following procedure, and a blank determination shall be run. <br /> 4.5.7.1.1 Test procedure. Place 10 grams of the undiluted sample in a <br /> 200 mi. flask. Add 5 grams of cuprous chloride and 75 ml. of concentrated <br /> hydrochloric acid. Mix well and insert a thermometer. Arrange a flask and <br /> a condenser for downward distillation. All rubber stoppers to be used must <br /> be wast-.ed in carbon disulfide, boiled in 61 hydrochloric acid and dried <br /> thcrca�hly. Distil 35 m1. of the mixture into a 400 ml. beaker containing <br /> 150 of cold eater. Before distilling, the beaker and Eater should be <br /> cooed in an ice bath. During distillation, the condenser tip mist to below <br /> the st:.rface of the water in the beaker, and the process mu.-, be vatcac-! care- <br /> fully tu <br /> o avoid sckbsck. if the temperature cf tae vapor ex.e�ws 1C °_ <br /> at any time, cease the distillation icssiiately, cc_1 tic and <br /> add al, of concentrated hydrochloric acid. Then the dictillat.on rX1f be <br /> coati_-_ed. After completing the distillation, caref'�lly aid must f: iect <br /> 25 percent sodium hydroxide to turn red litmus to blue. Then add �i t enot.gh <br /> 6N :,;;:i..-ochloric acid to change the solution back to acli. Aid 15 to <br /> of :old saturated sodium bicarbonate solution, one Ram of potassium _glide <br /> cryst" and 5 al. of a one percent starch solution. Stir Lntil the potas- <br /> siva iodide crystals have dissolved. Titrate the mixture with 0.03Y iodine <br /> solution until the color becomes slightly purple. Calculate the percent <br /> arsenic as follovs: <br /> Percent arsenic •75 (A)(N) <br /> W <br /> Where: A - al. of iodine solution used <br /> M • normality of iodine solution <br /> Y = veight of sample in Rams <br /> 10 <br /> 1�tb <br />