BARK. 53 



On its arrival at the works the bark usually contains from 8 to 12 

 per cent of water. Fresh bark does not } T ield the acid readily. Hence 

 when possible it is stored until fully cured, usually between one and two 

 years. It is highly important to keep it well protected from rain, for 

 it leaches easily and is soon ruined. For the same reason, bark from 

 logs which have been towed or driven is of little value. Salt water 

 ruins it entirely. If well cared for, nearly all the tannin in the bark is 

 available. A cord of Eastern bark yields from 400 to 430 pounds of 

 extract, which is sufficient to tan from 200 to 225 pounds of sole 

 leather, or a trine more of upper leather. 



At present the available supply of hides in the Pacific Northwest is 

 insufficient to support a tanning- industry of any great proportions. 

 It is probable that before there is a home market for any considerable 

 quantity of bark it will be required to supply tanneries in the East, 

 where complaint is already made of an inadequate supply. If this 

 proves true, the product must be shipped in a condensed form and 

 considerable capital will be required to develop the industry. 



EXTRACT. 



The process of making the extract is as follows: The bark is ground 

 and placed in wooden vats, where it is steeped until the acids are 

 removed. The resulting liquor is then evaporated in a vacuum at a tem- 

 perature of about 180° F. until it is reduced to a heavy, dark colored fluid 

 weighing about 10 pounds to the gallon and containing nearly all the 

 tanning properties of the bark. Assuming the unsteeped bark to have 

 10 per cent of tannic acid, 100 pounds of it would produce about 40 

 gallons of 20° liquor, which, upon analysis, would show about 2£ per 

 cent of tannin. The extract is usually shipped in 500-pound barrels 

 and brings about 2£ cents a pound. 



While the production of ground tan bark for local use is a simple 

 process, the successful manufacture of extract requires even more 

 expensive machinery than the manufacture of lumber. In the East, 

 where machinery is cheaper than on the Pacific coast, a 10-barrel 

 plant costs from $15,000 to $20,000. The leach house is much like 

 that of a tannery, but an evaporating plant is also required in which 

 all vats and pipes must be copper or brass lined, and this part of the 

 establishment representsa large proportion of the entire expense. It 

 is also customary to conduct a barrel factory in connection with the 

 plant. From these considerations, it is apparent that extract works 

 will be built only where there is certainty of a sustained bark supply 

 and that, owing to the cost of transportation. Hemlock will probably 

 be more valuable where it occurs in sufficienl quantity to support a 

 factory than in regions where the bark must be sent a distance to 

 market. 



