Bark and Bai'k- stripping. 825 



of sloes , and his frieDcl Mr. Poole, of Stowey, made the more palatable 

 discovery that it exists in port wine. 



Hides stripped of the hair and outer skin consist wholly of gelatine, 

 which is easily soluble m water, and which forms when combined with 

 water the jelly called glue. The tannin of bark, which is an antiseptic, 

 is also readily soluble in water, and then combines with the gelatine of 

 the hide, and the two together produce a substance highly imputrescent. 

 The fixed acids, querci-tannic and gallic, have the power of preventing 

 decay in animal and vegetable fibre, and are abundant in oak bark. 



While the tannin principle of the bark, by contracting the pores, 

 enables the leather to resist the action of air and water, and to with- 

 stand putrescent tendencies, softness and durability in the leather 

 produced are to a great extent due to the presence of another substance 

 found in bark, and called by the chemists extractive. This substance 

 resides mainly in the brown or middle part of the bark ; while the 

 white cortical layers next the alburnum, or sapwood, and which are 

 generally most abundant in young trees, contain the largest amount of 

 tannin. The epidermis, or skin, supplies neither. 



Leather prepared by most of the chemical substances now so freely 

 used, or by an infusion of galls, cracks ; and that prepared with birch 

 bark is more or less fragrant. 



It has been ascertained that the bark of trees under twenty years 

 old has not arrived at perfection ; while after thirty years it becomes 

 more corky, and diminishes in the yield of both tannin and extractive. 

 Spring-stripped bark, also, contains more than four times the quantity 

 of tannin which can be found in tlie same weight of bark cut from the 

 trees in winter. The astringent property varies according to the age 

 of the trees, being most abundant in those of middle age and vigour. 



When the cost of labour was much lower than at present, and bark 

 realized a higher price in the market, a considerable quantity of oak 

 coppice was cultivated principally for its bark, and rotations of twenty- 

 four or twenty-six years were found most remunerative. The stools 

 were generally most productive at distances of about 8 feet apart ; and 

 the shoots were thinned out at the end of the second year and 

 subsequently pruned. The great reduction in price consequent upon 

 the large importations of foreign bark, and the free use of chemicals, 

 have materially lessened such cultivation. 



Monteath maintained that the bark from a natural stool of oak wood, 

 at the age of twenty-four years, equalled in weight that from an oak 

 tree fifty years old, while the quality of the former was greatly 

 superior. 



At one time, any kind of bark containing a considerable per-centage 

 of tannin was marketable, including the Spanish chestnut, willow, and 

 mountain ash, and later still the birch and larch. But the large 



