BS ISO 788:2021 pdf download – Ultramarine pigments 7.2Reagents and materials Use only reagents of recognized analytical grade and water of at least grade 3 as specified in ISO 3696. 7.2.1Sodium sulfite, anhydrous,CAS-No 7757-83-7. 7.2.2 Formaldehyde solution. Dissolve 8 ml formaldehyde solution [37,0 % to40,0 %(mass fraction).CAS-No 50-00-0] and dilute to 100 ml. 7.2.3 Acetic acid solution, 30 % (volume fraction). Dissolve 30 ml acetic acid [99,5 %(mass fraction).p=1,42 g/ml , CAS-No 64-19-7] in water and dilute to 100 ml. 7.2.4 lodine solution. Weigh 0,13 g iodine (CAS-No 7553-56-2) and 0,35 g potassium iodide (CAs-No7681-11-0) and dissolve in 100 ml water, transfer into a brown bottle and dilute to 1 000 ml. 7.2.5Sodium thiosulfate standard titration solution, c (NazS203)= 0,1 mol/1. 7.2.6Soluble starch solution,5 g/l. 7.2.7 Sodium thiosulfate standard titration solution, c(NagS203)=0,002 mol/l.Dilute the sodiumthiosulfate standard titration solution (7.2.5) with water. 7.3Apparatus Use ordinary laboratory apparatus and burettes, pipettes and one-mark volumetric flasks in accordancewith the requirements of ISO 385, ISO 648 and ISO 1042, respectively, together with the following. 7.3.1 Conical flask, 250 ml with a narrow neck and equipped with a ground-glass stopper.7.3.2Volumetric flask, 250 ml. 7.3.3Pipette, 20 ml, 25 ml, 50 ml.7.3.4Electric heating board. 7.3.5 Burette, 50 ml, graduated in 0,1 ml divisions.7.3.6 Balance, with an accuracy of o,1 mg. 7.4 Procedure 7.4.1 Preparation and determination of the test solutionCarry out the determination in duplicate. Weigh about 7 g to 10 g (to the nearest 0,1 mg) of the sample into a 250 ml conical flask (7.3.1) and add 5 g of anhydrous sodium sulfite (7.2.1) and 70 ml water. Boil under reflux for about 15 min, then cool down to room temperature and transfer the mixture into a 250 ml volumetric flask (7.3.2). Dilute the solution to scale with water and mix well. Store the mixture for about 60 min or separate it using a centrifuge. Remove 25 ml of the supernatant fluid using a single-line pipette and pour it into a 250 ml conical flask. This is the test solution. Add 50 ml formaldehyde solution (7.2.2) to the test solution, shake it for 5 min. Add 5 ml acetic acid solution (7.2.3), stir the mixture evenly and add a known volume of iodine solution (7.2.4) (usually 50 ml) to ensure the presence of excessive iodine. Gently shake the solution mix it completely, add soluble starch solution (7.2.6) and titrate the excess iodine with sodium thiosulfate...

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