104 Comlination of Tannin and a vegetable Matter. 



thickness, when they are boiled or evaporated. It is to this 

 that the sediments are owing which are formed in some 

 infusions when they cool, and which are dissolved after- 

 wards with more or less difficulty. It is this substance 

 also, perhaps, which, as well as some other combinations of 

 difterent vegetable principles with which it rnay be mixed, 

 has been taken for more than half a centurv for a peculiar 

 principle, and which has been denominated the extract of 

 plants. This is certainly the case with the astringent plants, 

 and particularly the roots, wood, bark, Sec. which have this 

 character. 



It would be very interesting to examine with care, and 

 with the views above pointed out, the extracts which are 

 prepared by the apothecaries, and to inquire if the name of 

 extractive matter, adopted since 1787, in order to designate 

 homogeneous principle in plants, ought to be retained ia 

 the present slate of science. 



While we expect that something more will be done on this 

 subject, we beg leave to assure our readers, that the vegetable 

 substances employed as body-colours in dyeing, and in giving 

 a brownness to common cloths, contain a combination ot" 

 tannin and animal matter: of this nuinber are chiefly the 

 bark of the alder tree, of the ash, the green shell of wal- 

 nuts, &c. : to these we may add the Indian chesnut-tree, 

 since the compound of tannin contained in its leaves unites 

 very easily with wool, silk, and even cotton ; and the co- 

 lours thus given appear very solid. 



We are inclined to think, therefore, that the theory of 

 dyeing may acquiresomeioiprovementsfrom a precise know- 

 ledge of a compound hitherto unknosvn in plants, and 

 which acts a peculiar part in the production of colours ap- 

 plied without previous preparation upon cloths. 



It results, for instance, from our inquiries, that, in order 

 to fix the colouring matter of woods and barks upon cloths 

 of vegetable origin, it would perhaps be advantageous to 

 prepare them first with animal liquors, in order to precipitate 

 more abundantly the tannin and the tannated substance, 

 which it renders more soluble: there is even reason to be- 

 lieve that this process is already in use in some manufac- 

 tories. 



Miffht we not also be permitted to ascribe to the same 

 combination a physiological use with respect to seeds, and 

 to acknowledge in the chemical composition of their en- 

 velopes an anxiety on the part of nature to preserve them by 

 covering them with an insoluble and imputrescible sub- 

 stance? What we have discovered as belonging to the skins 



of 



