TANNING MATERIALS. 149 



EXPERIMENTS L^poN OAK-BARK FOR TANNING- PURPOSES, BY DR. 

 BAUER, OF WURTEMBURG. 



The growing importance of questions relating to the supply of tan- 

 ning materials, for which the forester must provide, induced Dr. Bauer, 

 one of the professors of the Forest Academy at Hoheuheim, and director 

 of experimental forest-stations in Wiirtemburg, to undertake in 1872 a 

 series of observations with a view of settling some of these questions. 

 Without following in detail the methods pursued, we will state the prin- 

 cipal conclusions at which he has arrived. It may be remarked that 

 observations were undertaken in France, in 18G6, for this same object, 

 by M. Bouvart, a forest inspector, and that there is a general agree- 

 ment of results, allowances being made for differences due to soil, ex- 

 posure, and climate between places widely separated. In fact, this 

 agreement appears to indicate that these influences have really less 

 effect than had been formerly supposed. 



It is generally admitted that we have not sufficient means for determining the vol- 

 ume and the absolute and specific weight of oak-bark, whether green or dry, or whether 

 growing in the forest or in open fields, nor to estimate the yield of bark," although all 

 of these data are of great economic and scientific importance. The forester may be 

 called upon to estimate as exactly as possible the bark on a given cutting, which may 

 jierhaps be sold in advance, because the purchasers need to know upon what to de- 

 ])eud. The manner of keeping accounts may likewise require a change of expression 

 from one unit of reckoning to another, as, for example, from quintals to cubic meters. 

 A knowledge as to the lo-s of weight in bark by drying is also of great importauce, 

 not only in a scientific but in an economical point of view, because bark in wet years 

 must often be transported in a green st.ote. Finally, we cannot exactly determine the 

 money value of oak fit for peeling without knowing the relative yield of bark and 

 wood. 



Although certain research had been made upon this subject, they needed confirma- 

 tion by new examination, for which reason the commission chai'ged with the direction 

 of certain German forestal experiments, decided to undertake more extended observa- 

 tions concerning bark suitable for tanning. To obtain a more speedy conclusion, these 

 experiments were in Prussia, made upon oJd,'^ and in Baden and Wiirtemburg upon 

 yoiuig trees. 



In Wiirtemberg, oak-bark is divided for market into the three following sorts: 



1. Glossy or shiniug hark, obtained from all trees less than 12 centimeters (4^ inches) 

 in diameter, including the bark, whether creviced or not. 



2. Average bark, i. e., bark both of stem and branches, from trees and shoots cut la 

 the working of /itfaie,^ and from 12 to 24 centimeters (4^ to 9 inches) iu thickness. 



3. Coarse bark, including the bark of trunk and of all branches of trees over 24 

 centimeters iu diameter. 



The price of the second is generally seven-tenths as much as the first, and the third 

 is sold separately, the unit in all cases being the quintal. 



Glossy bark is" found chitfly in copi>ices managed specially for the production of bark, 

 with a revolution of fifteen to thirty years, or in the underwood of coppice mingled 

 with large timber; or, less frequently, in the trees cut iu the lirst thinning of futaie 

 Average bark comes chiefly from the younger reserves of coppice, mingled with large 

 timber, and thinning of trees fifty to eighty years old. Coarse bark comes from old 

 oaks, of all descriptions, wherever it appears worth saving, The experiments reported 

 related chiefly to the first and second of these classes. 



The experiments are described in detail, and tables are given in thirty-six separate 

 cases, varied to meet as many different conditions as was practicable, and in each case 

 showing — 



The weight of green wood not peeled. 



The volume of wood not peeled. 



The specific gravity of wood not peeled. 



The weight of green wood peeled. 



' The term " Vieilles ^corces," used in the article in lievue des Eaux et Forels, from 

 which we translate, is more strictly applied to trees left at the fifth revolution or 

 thinning, by which forest-reserves are brought to their full maturity. 



"Term aijplied to a forest raised to full maturity, and from which portions are 

 thinned out from time to time. 



