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4 2 VolatIle matenals may be lost when the sample temperature nses durmg the sulfunc aCId addItIon step To mlmmlze thIS loss the flask should be cooled durmg additlOn of the sulfunc aCId solutlOn 43 Chlondes are quantitatively oXIdIzed by dIchromate and represent a posItive mterference Mercuric sulfate IS added to the digestlOn flask to complex the chlorides, thereby effectively ehmmatmg the mterference on all but brine and estuarine samples 5. Apparatus 5 1 Reflux apparatus Glassware should consIst of a 500 ml Erlenmeyer flask or a 300 ml round bottom flask made of heat-resIstant glass connected to a 12 mch Alhhn condenser by means of a ground glass Jomt Any eqmvalent reflex apparatus may be substituted provIded that a ground-glass connectlOn IS used between the flask and the condenser 6 Reagents 6.1 DIstIlled water SpecIal precautlOns should be taken to msure that dIstIlled water used m thIS test be low m orgamc matter 62 Standard potassIUm dIchromate solutiOn (0 250 N) DIssolve 12259 g K2Cr207, primary standard grade, previOusly dried at 103°C for two hours, m dIstIlled water and dIlute to lOOOml 63 Sulfuric aCId reagent Conc H2S04contammg 23 5g sIlver sulfate, Ag2S04, per 409kg bottle WIth contmuous stIrnng, the sIlver sulfate may be dIssolved m about 30 mmutes 6.4 Standard ferrous ammomum sulfate (025 N) DIssolve 98 0 g of Fe(NH4)2(S04)2.6H20 In dIstIlled water Add 20 ml ofconc H2S04(6 8), cool and dIlute to 1hter ThIS solutiOn must be standardIzed dally agamst standard K2Cr207 solutiOn (6 2) 64 1 StandardIzatiOn To approXImately 200 ml ofdIstIlled water add 250 ml of0 25 N K2Cr207 (62) solutiOn Add 20 ml of H2S04 (6 8) and cool TItrate wIth ferrous ammOnIumsulfate(64)usmg3dropsofferrommdlcator(66) Thecolorchange IS sharp, gomg from blue-green to redillsh-brown Normahty = (ml K,Cr,O¥O 25) ml Fe (NH.h (SO.), 6.5 Mercuricsulfate PowderedHgS04 6.6 Phenanthrohne ferrous sulfate (ferrom) mdlCator solutiOn DIssolve 148 g of 1-10 (ortho) phenanthrohne monohydrate, together wIth 0 70 g of FeS04·7H20 m 100 ml of water ThIS mdlcator may be purchased already prepared 67 SIlver sulfate Powdered Ag2S04 6.8 Sulfuric aCId (sp gr 1 84) Concentrated H2S04 7 Procedure 7 1 Place several bOllmg stones m the reflux flask, followed by 50 0 ml of sample or an alIquot dIluted to 500 ml and 1 g of HgS04(6 5) Add 50 ml conc H2S04(6 8), SWIrl untIl the merCUriC sulfate has dIssolved Place reflux flask 1ll an Ice bath and slowly add, wIth sWlrhng, 250 ml of 025 N K2Cr207 (62) Now add 70 ml of sulfuric aCId-sIlver 410 1-2 Iill 1111 III I II I11 III1 I I IIPDF Image | Methods for Chemical Analysis of Water and Wastes
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