TANNIN EXTRACT PROCESSES. 21 



The vapor is condensed in a receptacle high enough above the pan 

 to permit a 34-foot vertical waste pipe. This pipe, kept full of water, 

 supplies a water column sufficient to offset the atmospheric pressure 

 and maintain the vacuum. 



A cord of dry bark, 2,200 pounds, is reduced to 50 gallons of 

 extract, which weighs about 550 pounds. The extractor has a 

 capacity of 12 cords a day. 



SUPPLEMENTAL MATERIALS. 



The duration of the bark supply from tanbark oak will be extended 

 somewhat by the use of other materials as supplements or substi- 

 tutes. The superiority of the product of the tanbark oak over all 

 other Pacific coast barks is due not altogether to its high percentage 

 of tannin, but rather to the quality of the particular tannin con- 

 tained in it, and perhaps also to the presence of certain other acids, 

 such as gallic and acetic. The value of this combination is proved 

 by tanning experience. Mixing imported tanning materials, such 

 as gambier and quebracho, increases its effectiveness and counter- 

 acts some of its undesirable qualities. As tanners have learned the 

 use and value of these supplementary agents, methods have been 

 more and more adapted to them, until to-day they are regarded as 

 indispensable and the tanbark oak product is never used alone. 



As the accessible supply of tanbark oak grows scarcer and dearer, 

 the bark from other species of oak is occasionally mixed with the 

 superior material. This is especially the case in the southern dis- 

 tricts, where the tanbark oak is more nearly exhausted. The barks of 

 the California black oak and the coast live oak run so high in tannin 

 that if tannin content alone were an index of tannage value they 

 could compete with tanbark oak. They can not be used alone, 

 because they will not produce leather of goo'd quality; the live-oak 

 bark in particular imparts a gritty character to the leather, which 

 ruins the knives of the cutters, but mixed in moderate quantities 

 with the better bark they make possible a considerable saving. 



Alder bark is occasionally found in shipments of bark from tan- 

 bark oak, but the tree does not grow in sufficient quantity in Cali- 

 fornia to be a factor in bark supply. In the Mendocino woods the 

 chinquapin is often peeled, but it contains so little tannin that it is 

 practically worthless. Moreover, it is very fibrous and tough, which 

 makes it difficult for the smaller tanbark mills to handle. 



Analyses of average bark samples from the main trunks of the 

 important California trees are given in Table 10. Some of these 

 have never been subjected to commercial experiment. 



