ASTM-D444:88(R2020) pdf free download – Standard Test Methods for Chemical Analysis of Zinc Yellow Pigment (Zinc Chromate Yellow).
22. Reagent
22. 1 Silver Nitrate Solution (17 g/L)—Dissolve 1 7.0 g of AgNO1 in water and dilute to I L.
23. Procedure
23.1 Weigh a 10-g specimen into a 600-mL beaker. Add 200 rnL of water and 50 mL of nitric acid (HNO1) (2+3). Warm just enough to dissolve the spccimen. Filter to remove insoluble material. Add a slight excess of AgNO1 solution (17 gIL) (Note 12). Boil ftr 5 mm and let stand ft)r about 2 h.
NOTE 12—If care is exercised in adding hut a slight excess of AgNO3 solution, no silver chrornate (Ag2CrO4) will form. About 10 to 15 mL of AgNO3 solution (17 gIL) is usually not too much.
23.2 If no crystals of Ag,Cr04 are present, filter at room
temperature through a tared. tine-porosity sintered-glass crucible, using suction. Wash the precipitate free of AgNO3 with HNO (1+99). To be sure that an excess of AgNO3 was used, test the filtrate by adding a few drops of HCI (2+3). Dry the precipitate at 105 ± 2°C for 2 h, cool, and weigh as silver chloride (AgCI).
23.3 If crystals of Ag,Cr04 are present (Note 13), filter the solution through a line-porosity sintered-glass crucible and discard the filtrate containing most of the chromium. Dissolve the AgC1 precipitate by pouring 100 rnL of hot ammoniurn hydroxide (NH4OH) (1+5) slowly through the crucible while applying gentle suction. Catch the filtrate in a clean flask, taking care not to lose any of it. Wash with a few millilitres of HNO3 (sp gr 1.42) and then with a little more NH4OH (1+5).
NOTE 13—Silver chromate is difficult to dissolve completely by washing with dilute HNO3 hence, in such cases. it is necessary o dissolve in NH4OH and reprecipiate.
23.4 Transfer the solution to a beaker and make it faintly acid by adjusting with either HNO1 (1+5) or NH4OH (1+5) as required. Add a few drops of AgNO solution (17 gIL) and boil for 5 mm. Let stand at least 2 h in a dark place. Filter through a tared, line-porosity sintered-glass crucible, using suction.
24. Procedure
24.1 Weigh to 0.1 g about a I 0-g specimen (Note 14) and place in a 600-mL beaker. Add 300 mL of acetic acid (1+9). Heat the mixture to 80°C and maintain at 80 ± 5°C, while stirring, until nothing further dissolves. Filter while hot through a tared Gooch crucible. Wash the insoluble residue on the filter with hot water.
Note 14—If the pigment contains an organic treating agent, first remove this treating agent by washing with ether or chloroform.
24.2 Dry the crucible at 105 ± 2°C and weigh.
24.3 Calculation—Calculate the percent of matter insoluble in 10 % (by volume) acetic acid F as follows.