Treating processes, Tannin Solutizer

Hydrolysed, polynuclear Cr complexes are of considerable commercial importance in the dying and tanning industries. In the former the role is that of a mordant to the dye. In leather production it is necessai to treat animat hides to prevent putrefaction and to render them supple when dry. Traditionally, tannin was used, hence the name of the process, but this was superseded towards the end of the nineteenth century by solutions of chromium(lil) sulfate. After soaking in sulfuric acid the hides are impregnated with the Cr solution. This is subsequently made alkaline, when the polynuclear complexes form and bridge... 

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