Leather titration

There have been approximately 80 references to oxazine dyes in the past 15 years. Several are references to their use as laser dyes and titration indicators. Thirty of these references are to oxazine dyes for either acryUc fibers or leather (qv) (7) (see Fibers, acrylic). 

Potassium chromate is used in enamels rustproof metals and leather finishes. The compound also is an indicator in argentometric titrations. 

Oxazine, azine and thiazine dyes are named for the characteristic heterocyclic ring systems 1,4-oxazine, 1,4-diazine, and 1,4-thiazine. The dyes are generally cationic (basic) or acid dyes. They also can be reduced to colorless forms, then oxidized back to the dye, as in vat dyeing. The dyes also have been used to a limited extent in disperse and fiber reactive applications. They are used as titration indicators and may be applied to acrylic fibers and leather. 

Red Dye No. 2 was formerly used in food, drugs, and cosmetics but was banned by the US Food and Drug Administration (FDA) in 1976. It is currently used in the United States for dyeing wool, silk, and other textiles as well as paper, wood, and leather products. It is also used as an indicator in hydrazine titrations and is used in color photography and in the manufacture of phenol-formaldehyde resins. Red Dye No. 2 continues to be widely used in food, drugs, and cosmetics in other countries. 

No matter what the source of chromium tannages, either from raw materials or from recycled solutions, care must be taken to maintain the quality of the leather. This can be only achieved by constant chemical analysis and chemical control. The chromium content in the solution can be tested by the following two methods, titration and atomic absorption analysis ... 

Add 30 ml of phosphoric acid (H PO, 40%) and 20 ml potassium iodide (K110%) to the solution obtained by digestion. Keep the solution standing for 5 min. Titrate the solution with a 0.1 N standard solution of sodium thiosulphate (Na SjO ) until the colour of the solution turns to yellow. Add 2-3 ml of starch solution (1% w/w) as an indicator. The colour of the solution turns to dark blue. Continue titration until the colour just disappears. Record the volume (V(,ml) used of the standard solution of Na,S, O. . The percentage of chromic oxide in leather can be calculated by the following equation ... 

Methanoic acid (HCOOH) is used in the processing of leather. To determine the concentration of methanoic acid in the process residue, chemists can titrate the residue with a base. Suppose a 75.0-mL sample of residue is neutralized by 42.0 mL of 0.200M NaOH. What is the molarity of methanoic acid in the residue (Assume the residue contains nothing hut methanoic acid and water.)... 

Protein binding has been used in various guises as a method for analysis of tannins and tannin-containing extracts. The hide powder method has been used for decades in the leather industry. More recently, methods based on the residual absorbance of unprecipitated hemoglobin (10), radiometric titration with labelled bovine serum albumin (BSA) (51), and the ferric chloride induced color of protein-tannin complexes resolubilized in alkali (50) have all been suggested as methods of tannin analysis. 

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