36 ANIMAL PROTEINS 



are supplied in form of a solid or concentrated liquid. Such 

 extracts- only need to be dissolved in warm water in order 

 to make a tan liquor, and the cost and trouble of leaching 

 is avoided. They are a great convenience as making 

 strong liquors of definite strength. Many vegetable tanning 

 materials are too weak in tan for the tanner to leach, and 

 indeed to justify the cost of importation have been made 

 available by manufacturing an extract at the source of the 

 material. With such weak materials the extract manu- 

 facturer has had to secure a much more complete extraction 

 than in ordinary leaching, and to concentrate his infusions 

 by means of steam-heated vacuum pans. With such 

 experience he has naturally begun to make extracts also 

 from the stronger materials, such as myrabolans and 

 mimosa bark, and it is now possible to have a tannery 

 without any leaches at all. Tanners also have begun to 

 realize the advantages not only of more rapid and complete 

 extraction, but also of doing the work for themselves, and 

 extract factories are beginning to appear as an adjunct to the 

 larger tanneries. The more complete extraction of tan also 

 involves a greater extraction of unwanted colouring matters, 

 hence decolorization is a feature of extract manufacture. 



Chestnut Extract is from the wood of the Spanish 

 chestnut (Castanea vesca), which contains 3-6 per cent, of 

 a valuable pyrogallol tan very similar to that of valonia. 

 Its weight-giving and water-resisting powers are as good 

 as valonia, and its penetrating power is even better, so that 

 it forms an exceedingly suitable material for the modern 

 short tannage, and also for drum tannages. The extract 

 is manufactured extensively in France. The wood is stripped 

 of bark and usually piled for some months to dry and to 

 allow the resins to become insoluble. Some factories, 

 however, use the green wood direct. There are two methods 

 of extraction, viz. in open vats and in closed vats under 

 pressure. The two methods yield extracts which differ in 

 composition and properties. In either case the vats have 

 a capacity of up to 3000 gallons, and hold up to 6| tons 

 of wood. They are arranged in series, as in leaching, and 



