38 ANIMAL PROTEINS 



The manufacture is also similar to that of chestnut 

 extract, but decolorization is often omitted, and greater 

 care has to be taken and in other ways to keep the colour 

 within limits. One of these is to strip the wood more 

 completely of bark. Another is to operate at as low a 

 temperature as possible, about 110 C. The extraction is 

 made in large circular vats about 14 feet high and holding 

 about two tons material. A battery is composed of about 

 eight vats or extractors. Open extraction is used, and 

 the liquor is passed forward after 2-3 hours' boiling, so 

 that the material is spent in about 24 hours. A liquor of 

 about 5 Be (36 Bkr.) is obtained, and the strength of the 

 material reduced from 4 to J per cent, of tannin. Getting 

 rid of insoluble matter is a difficulty, and is attained by 

 settling, by rapidly cooling, and then passing through a 

 filter press of wood. For evaporation a double-effect 

 vacuum pan is preferred, which operates first at about 

 113 F., and afterwards at 140 F. with a higher vacuum. 

 The liquor is concentrated from 5 to 25 Beaume (s.g. 

 1/036 and i -210 respectively). 



The extract has a much higher colour than chestnut, 

 and is not used now as much as some years ago. As the 

 principal supply was German, it has been unavailable. 



Quebracho Extract is made from the wood of the 

 South American tree Loxopteryngium Lorenzii, which con- 

 tains about 20 per cent, of a typical catechol tan. It is 

 associated with a little catechin, much phlobaphene, but 

 practically no sugar. The tannin is very astringent, 

 penetrates quickly and gives a firm red leather which darkens 

 on exposure to light. It is not noted for weight-giving 

 powers. The wood itself, as chips or shavings, has been 

 used in British tanneries, to a limited extent, but the great 

 bulk of the material is made into extract chiefly in South 

 America. The crude " extract," made by evaporating 

 aqueous infusions of the wood, is largely exported for 

 refinement in Europe. It is also refined on the spot to a 

 large extent and converted into solid extract containing 

 60 per cent, of tannin. 



The great difficulty with quebracho has been the disposal 



