BARK. 53 



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

 per cent of water. Fresh bark does not yield the acid readil3\ Hence 

 when possible it is stored until fully cured, usuall}^ between one and two 

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

 it leaches easilj^ and is soon ruined. For the same reason, bai'k 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 trifle more of upper leather. 



At present the available supplj^ 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 suppl}- tanneries in the East, 

 where complaint is alread}' made of an inadequate suppl3\ If this 

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

 considerable capital will be required to develop the industry. 



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 anal3"sis, would show about 2^. per 

 cent of tannin. The extract is usually shipped in 5<)0-pound barrels 

 and brings about 2i 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 represents a large proportion of the entire expense. It 

 is also customary' to conduct a barrel factorj^ 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 sufficient quantity to support a 

 factory than in regions where the bark must l)e sent a distance to 

 market. 



