2.90 NOTES ON TANNING SUBSTANCES. 



to the presence of a greater or less degree of gallic acid, is not un- 

 derstood. " Proust has supposed, in his paj)er on Tannin, that 

 there exist different species of tanning principle, possessed of different 

 properties and different powers of acting upon reagents, but all pre- 

 cipitable by gelatine. This opinion is sufficiently conformable to the 

 facts generally known concerning the nature of the substances which 

 are produced in organised matter ; but it cannot be considered as proved 

 till the tannin in different vegetables has been examined in its pure or 

 insulated state. In all the vegetable infusions which have been subjected 

 to experiment, it exists in a state of union with other principles, and its 

 properties must necessarily be modified by the peculiar circumstances of 

 its combination." — (Davy on Tanning.) 



An experienced judge can tell from the colour of his raw tanning material 

 very nearly what the colour of the leather tanned with it will be. Thus, 

 for instance, take a first-rate sample of carefully-dried English oak bark ; 

 observe the colour of the interior cortical layer, and compare it with a 

 sample of the best pure English oak-bark tanned leather, and it will be 

 seen that they are comparatively of the same colour : the leather will be 

 the darkest, owing to the red colour of the epidermis. Also compare apiece 

 of the best Sardinian cork-tree bark with the leather tanned with it : 

 the leather will be of a reddish hue, very similar in colour to the bark 

 itself. The same thing may be observed in hemlock, alder, and mimosa 

 barks, and in almost every other land of tanning material. Pure valonea- 

 tanned leather is very similar in colour to the valonea itself. The way to 

 find out what the colour of the " bloom " of any tanning material is, is to 

 make a decoction and allow it to stand a few days, when the " bloom," if 

 any, will deposit. 



Some materials simply tan leather, but will not "fill up "the pores of 

 the hide, and only make a porous and poor leather ; while others " fill up " 

 the hide, and make good and firm leather. The cause of this would form a 

 very interesting and profitable subject for investigation. 



" The Conifers are natives of various parts of the world, from the 

 perpetual snows and inclement climate of Arctic America to the hottest 

 regions of the Indian Archipelago. The principal part of the order is 

 found in temperate countries, in Europe, Siberia, China, and the temperate 

 parts of North America. The species are exceedingly abundant, and have an 

 aspect very different from that of the Southern hemisphere. In the 

 former we have various species of pines, the larch, the cedar, spruce and 

 juniper, the place of which is supplied in the latter by araucarias, podo- 

 carps, dammars, and dacryds." — (Lindley.) 



Hemlock Spruce (Abies Canadensis). — " This tree is natural to the 

 coldest regions of America, and constitutes three-fourths of the evergreen 

 woods in Nova Scotia, New Brunswick, Maine, Vermont, and part of New 

 Hampshire. It is also very common in Canada. It is less common further 

 south, but is found in the Middle and Southern States. On the Alleghanies 

 it grows to a height of 70 to 80 feet, with a uniform circumference for two- 



