The apparatus (see Figure 2.4.2.-1) consists of a 100 mL conical flask closed with a ground-glass stopper through which passes a glass tube about 200 mm long and of internal diameter 5 mm. The lower part of the tube is drawn to an internal diameter of 1.0 mm, and 15 mm from its tip is a lateral orifice 2 mm to 3 mm
in diameter. When the tube is in position in the stopper, the lateral orifice should be at least 3 mm below the lower surface of the stopper. The up-per end of the tube has a perfectly flat, ground surface at right angles to the axis of the tube. A second glass tube of the same internal diameter and 30 mm long, with a similar flat ground surface, is placed in contact with the first, and is held in position by two spiral springs. Into the lower tube in-sert 50 mg to 60 mg of lead acetate cotton R, loosely packed, or a small plug of cotton and a rolled piece of lead acetate paper R weighing 50 mg to 60 mg. Between the flat surfaces of the tubes place a disc or a small square of mercuric bromide paper R large enough to cover the orifice of the tube (15 mm × 15 mm).
2.4.2. 砷
方法A
设备组成（见图2.4.2.-1）：100ml具有玻璃塞的锥形瓶，塞上通过了一根长约200mm、内径5mm的玻璃管。玻璃管最下面的部分被拉至内径1.0mm，离末端15mm处有一直径为2-3mm的侧孔。玻璃管安装在瓶塞里，侧孔至少应在离塞子下部3mm处，玻璃管上部终端处完全为一平面，表面与管的轴心垂直。另一根玻璃管内径一样，长30mm，表面一样平，与第一根管相连，通过两根螺旋弹簧保持在同一位置。在玻璃管的下面装入50mg-60mg的醋酸铅棉花，松散地塞满，或一个小的棉花塞与一块重量为50mg-60mg的醋酸铅试纸。在两根玻璃管表面之间放一圆形或一小正方形的溴化汞试纸，大小足够能覆盖管子的小孔（15 mm × 15 mm）。
In the conical flask dissolve the prescribed quantity of the substance to be examined in 25 mL of water R, or in the case of a solution adjust the prescribed volume to 25 mL with water R. Add 15 mL of hydrochloric acid R, 0.1mL of stannous chloride solution R and 5 mL of potassium iodide solution R, allow to stand for 15 min and introduce 5 g of activated zinc R. Assemble the two parts of the apparatus immediately and immerse the flask in a bath of water at a temperature such that a uniform evolution of gas is maintained. Prepare a standard in the same manner, using 1 mL of arsenic standard solution (1 ppm As) R, diluted to 25 mL with water R. After not less than 2 h the stain produced on the mercuric bromide paper in the test is not more intense than that in the standard.
Introduce the prescribed quantity of the substance to be
examined into a test-tube containing 4 mL of hydrochloric
acid R and about 5 mg of potassium iodide R and add 3 mL of hypophosphorous reagent R. Heat the mixture on a water-bath for 15 min, shaking occasionally. Prepare a standard in the same manner, using 0.5 mL of arsenic standard solution (10 ppm As) R. After heating on the water-bath, any colour in the test solution is not more intense than that in the standard.
All solutions used for this test should be prepared with distilled water R.
To 0.2 mL of alcoholic calcium standard solution (100 ppm Ca) R, add 1 mL of ammonium oxalate solution R.
After 1 min, add a mixture of 1 mL of dilute acetic acid R and 15 mL of a solution containing the prescribed quantity of the substance to be examined and shake. Prepare a standard in the same manner using a mixture of 10 mL of aqueous calcium standard solution (10 ppm Ca) R, 1 mL of dilute acetic acid R and 5 mL of distilled water R. After 15 min, any opalescence in the test solution is not more intense than that in the standard.
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