Chapter XXII The Extraction of Tanning Materials, and the Making of Extracts
Leaching — Early forms of leaches — The press-leach system — Handling of liquors — Distributing troughs and valves — Construction of leaches — Influence of temperature — Use of silent boiling jet — Closed extractors — Sprinkling leaches — Manufacture of extracts — Decolorisation of extracts — Soluble extracts — Concentration of extracts — Yaryan evaporator — Multiple effects — The use of extracts in the tannery — Effect of temperature on extraction and colour PAGE 328