Tham khảo tài liệu 'a heat transfer textbook third edition by john h lienhard iv and john h lienhard v_2', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | APPENDIX B CHEMICAL ANALYSIS PROCEDURES B-l. EXTERNAL TREATMENT PLANTS a. Test for Hardness Colorimetric Titration Method . This test is based on determination of the total calcium and magnesium content of a sample by titration with a sequestering agent in the presence of an organic dye sensitive to calcium and magnesium ions. The end point is a color change from red to blue. It occurs when all the calcium and magnesium ions are sequestered. NOTE If the testing procedure of the equipment and or reagent supplier differs from the following procedure the supplier s procedure must be used. 1 Equipment. These are supplied by commercial concerns as test kits. Equipment includes a One 25-ml burette automatic complete. b One 210-ml casserole porcelain. c One 50-ml cylinder graduated. d One stirring rod glass 2 Reagents. a Hardness indicator. b Hardness buffer. c Hardness titrating solution 1 ml - 1 mg CaCOs. 3 Procedure. Measure 50 ml of the sample in the graduated cylinder and transfer it to the casserole. With the calibrated dropper add ml of hardness buffer reagent to sample and stir. Add 4 to 6 drops of hardness hardness is present the sample turns red. Add the hardness titrating solution slowly from the burette with continued stirring. When approaching the end point the sample begins to show some blue coloration but a definite reddish tinge can still be seen. The end point is the final discharge of the reddish tinge. More hardness titrate solution does not produce further color change. In using this procedure the hardness titrating solution must be added slowly because the end point is sharp and rapid. For routine hardness determination it is suggested that 50 ml of the sample be measured but only approximately 40 to 45 ml be added to the casserole at the start of the test. Add the hardness buffer reagent and the hardness indicator as directed and titrate the mixture rapidly to the end point. Then add the remaining portion of the sample. The hardness
