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