BOTANICAL ASPECTS OF PAPER-PULP AND TANNING INDUSTRIES 523 



Oregon and Washington, and it was claimed that modification of prevailing 

 logging practice, which prevented peeling of bark in usable form, could 

 increase the supply to 150,000 to 200,000 tons. 



For the most part, native x\nierican tree barks used in tanning have been 

 employed in the crude form, that is, crushed in some manner and then added 

 to the tanning vats where the tannins were leached from them. Since their 

 tanning content averages 10 per cent, it has always been necessary that 

 tanneries be located as close to tanbark sources as possible in order to elimi- 

 nate transportation costs on the 90 per cent waste material. Preparing aqueous 

 extracts of the bark near the source of supply as an operation apart from treat- 

 ing hides has been the means of obviating such cost and of permitting tanneries 

 to operate nearer their markets. A leaching patent toward this end was granted 

 as early as 1791, but ninety years later the census of 1880 still recognized only 

 three tanning agents — oak bark, hemlock bark, and sumac leaves which had 

 meanwhile come into use ; bark extract had not yet acquired any importance. 

 And by 1890, a century after that*first patent, only 5.6 per cent, by value, 

 of all tanning agents used were extracts. 



Subsequent development may have been greater, but in 1950 there were 

 only three hemlock and oak bark extract plants in California, Pennsylvania, 

 and Virginia, with a combined annual capacity of 32 million pounds of 25 

 per cent extract. 



Hemlock and oak bark were the backbone of the American tanning industry 

 until importation of foreign materials, discussed later, began at the close of 

 the nineteenth century. Since then they have for many years been the second 

 and third principal domestic sources, surpassed only by chestnut wood extract, 

 discussed next. And in the entire picture of vegetable tanning materials, as 

 shown in table 1, they occupied only eleventh place as a group in 1950. 



WOOD. Perhaps the most important technical discovery in the utilization of 

 native tannin sources was that contained in the communication of William 

 Sheldon in 1819 to the American Journal of Science, wherein he presented his 

 findings and views on the "x'\pplication of Chestnut Wood to the Arts of 

 Tanning and Dyeing." The bark of the European chestnut (Castanea sativa) 

 had been used in England as a substitute for oak bark, but now, for the first 

 time, attention was directed to the wood of American chestnut, containing 

 5 to 15 per cent tannin, as a possible industrial source of the material. Similar 

 pronouncement, regarding the European chestnut, has been credited to a 

 French chemist Michel, the same or the following year; and in 1870 chestnut 

 extract was manufactured in Europe. 



Like so many other significant discoveries, Sheldon's was not followed up 

 in America until just before the twentieth century when the abundance of 

 native chestnut {Castanea dentata) in the southern Appalachians provoked 

 the establishment of numerous chestnut wood-extracting plants in North 



