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ASTM D50-2019 pdf free download

ASTM D50-2019 pdf free download.Standard Test Methods for Chemical Analysis of Yellow, Orange, Red, and Brown Pigments Containing Iron and Manganese
11. Reagents
11.1 Stannous Chloride Solution (SnCl 2 ·2H 2 O)—Dissolve 50 g of SnCl 2 ·2H 2 O in 300 mL of hydrochloric acid (HCl) (sp gr 1.19) and dilute with water to 500 mL. Keep the clear solution in a tightly stoppered bottle containing some metallic tin. 11.2 Mercuric Chloride Solution (HgCl 2 )—Prepare a satu- rated solution of HgCl 2 (60 to 100 g/L). 11.3 Sulfuric-Phosphoric Acid Mixture—Mix 150 mL of sulfuric acid (H 2 SO 4 ) (sp gr 1.84) with 150 mL of phosphoric acid (H 3 PO 4 ) (85 %) and dilute with water to 1 L. 11.4 Diphenylamine Indicator—Dissolve 1 g of diphe- nylamine in 100 mL of H 2 SO 4 (sp gr 1.84). 11.5 Standard Potassium Dichromate Solution (K 2 Cr 2 O 7 ) (0.1 N)—Dissolve 4.904 g of K 2 Cr 2 O 7 in water and dilute to 1 L. Standardize against the National Institute of Standards and Technology standard sample No. 27 of Sibley iron ore. 11.6 Potassium Ferricyanide Solution (K 3 Fe(CN) 6 )— Optional. Dissolve approximately 0.01 g of K 3 Fe(CN) 6 in 50 mL of water. This solution must be made fresh when wanted because it does not keep.
12. Procedure
12.1 According to the amount of iron in the pigment, weigh 0.3 to 1.0 g of the pigment and ignite in a porcelain crucible at a dull red heat to destroy organic matter. Transfer to a 400-mL beaker and add 25 mL of HCl (sp gr 1.19). Cover with a watchglass and digest just short ofboiling (80 to 90°C) until no dark specks can be seen in the insoluble residue. The addition of a few drops of SnCl 2 solution after adding the acid greatly assists dissolving ofthe iron. When the residue is light in color, the solution ofiron may be considered complete. This may take from 15 min to 1 h, or longer. 12.2 Add 25 to 50 mL of water and heat to gentle boiling (avoid vigorous prolonged boiling). Slowly add SnCl 2 solution dropwise until the last drop makes the solution colorless or free from any tinge of yellow, then add 1 or 2 drops in excess. It is best to keep the watchglass on the beaker while adding the SnCl 2 solution, with agitation ofthe hot iron solution after each addition. Iftoo much SnCl 2 is added by mistake, add potassium permanganate (KMnO 4 ) to the solution until a yellow color appears, then again add SnCl 2 dropwise until the yellow color just disappears, again adding one or two drops in excess. Dilute with 200 mL of cold water; then add all at once with vigorous stirring 15 mL of HgCl 2 solution. Let stand 3 to 4 min. A slight white precipitate should form. If none, or a heavy grayish precipitate forms, the determination should be discarded and repeated. 12.3 Add 15 mL of H 2 SO 4 -H 3 PO 4 mixture and 3 drops of diphenylamine indicator solution. Titrate with K 2 Cr 2 O 7 solution, taking the sudden change of the dark green color to a blue-black color as the end point. 12.4 If preferred, K 3 Fe(CN) 6 may be used as an external indicator. In this case omit the addition of the H 2 SO 4 -H 3 PO 4 mixture and the diphenylamine indicator. Titrate with the K 2 Cr 2 O 7 solution as in 12.3, except toward the end take out a very small drop of the solution being titrated and touch this to a drop of the K 3 Fe(CN) 6 solution, best placed on a paraffined surface. Toward the end point the blue is replaced by a bluish-green coloration, perceptible at the junction of the two solutions. Take as the end point when no trace of the bluish- green coloration can be detected.

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