180 VEGETABLE SUBSTANCES. 



discover a substitute for oak bark. In that year the 

 Society rewarded with l()0 the person who first 

 applied oak sawdust to the purpose of tanning ; a dis- 

 covery which was adopted in Germany, and has been 

 continued with success. An attempt was likewise 

 made to apply the oak leaf to the same purpose. The 

 English tanners were, as they still are, slow to believe 

 that any thing which did not belong to the oak could 

 be efficacious in tanning. On inquiring, however, into 

 the subject, it was found that in other countries many 

 different substances were used. Heath pulverized, 

 gall-nuts, and the bark of the birch-tree, were em- 

 ployed in different provinces of Germany. In some 

 parts of Italy, myrtle leaves ; in Russia, the bark of 

 the willow ; in Corsica, dried leaves of wild laurel, 

 coarsely powdered ; in the island of St. Kilda, tor- 

 mentil root ; and in the West Indies, the bark of the 

 red mangrove tree. 



In 1766 a method was discovered of tanning leather 

 with heath boiled in a copper vessel, and applied to 

 the leather blood-hot; and a reward of ,700 was 

 granted by the Irish parliament to the inventors *. 



In order to prepare the oak bark for use, it was 

 formerly ground down by a heavy stone-wheel, turned 

 by a horse. Instead of this plan several persons now 

 use cast-iron cylinders, between which the bark is 

 passed, and it is thus more completely ground with 

 less labour. In the ordinary method of tanning, the 

 oak bark thus coarsely pulverized is put into a pit, in 

 alternate layers with the skins to be prepared. M. 

 Seguin found that much waste attended this method, 

 by which the whole of the virtues of the bark could 

 not be extracted, and that the using an infusion of 

 the bark was a much more economical practice. 



The experiments and discoveries made on this sub- 

 ject by that excellent practical chemist, were first pub- 

 * Macpherson. 



