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称取试样0.1～1克置锥形瓶中,用硝酸、盐酸、氢氟酸或其混合酸,加高氯酸加热冒烟(注1、2),冷却,沿瓶壁加入25毫升水,煮沸,移火,加亚砷酸钠(1%)5毫升(注3),放1～2分钟,流水冷却(注4、5),加入硫磷混合酸(1升溶液中含硫酸磷酸各200ml)30毫升,苯代邻氨基苯甲酸指示剂(0.02%)0.5毫升(注5),用0.0025N或0.025N亚铁溶液滴定。注(1)试样0.2、0.5、1克,高氯酸分别加2、4、7毫升.用氯化钠挥发去铬时,高氯酸多加3毫升. (2)一般样品微冒烟即可.工具钢必须充分冒烟,使钨酸凝聚。 (3)样品中不含锰时,滴加5%硫酸锰5滴.含铬10～20毫克时,亚砷酸钠加10毫升。
Weigh the sample 0.1 ~ 1g Erlenmeyer flask, with nitric acid, hydrochloric acid, hydrofluoric acid or its mixed acid, add perchloric acid heating smoke (Note 1, 2), cooling, along the bottle wall by adding 25 ml of water , Boil, heat transfer, sodium arsenite (1%) 5 ml (Note 3), put 1 to 2 minutes, water cooling (Note 4,5), add phosphoric acid (1 liter of solution containing sulfuric acid Each 200 ml), 0.5 ml of benzylanthranilic acid (0.02%) (Note 5) and titrated with 0.0025 N or 0.025 N ferrous solution. Note (1) 0.2,0.5,1 g samples, respectively, add 2,4,7 ml of perchloric acid with chromium chloride volatilization, perchloric acid add 3 ml more. (2) Tool steel must be fully smoked to allow the tungstic acid to condense. (3) When there is no manganese in the sample, 5 drops of 5% manganese sulfate should be added dropwise, and 10 ml of sodium arsenite should be added when containing 10-20 mg of chromium.