£onstilue7it Tarts of astringent Vegetalles. 75 



and the salts ; and that, of these compounds, such as con- 

 tahi tin are sUghtly soluble in water, whilst those that con- 

 tain iron are almost wholly insoluble. 



In examining the action of animal substances upon the 

 infusion of galls, with the view of ascertaining the compo- 

 sition of the compounds of gelatine and of skin with tan- 

 nin, I found that a saturated solution of gelatine, which 

 contained the soluble matter of 50 grains of dry isinglass, 

 produced from the infusion a precipitate that weighed nearly 

 91 grains; and in another instance, a solution jontaining 

 30 grains of isinglass gave abr^ut oQ grains ; so that, taking 

 the mean of the two experiments, and allowing for the small 

 quantity of insoluble matter in isinglass, we may conclude 

 that 1 00 grains of the compound gelatine and tannin, formed 

 bv precipitation from saturated solutions, contain'about 54 

 grains of gelatine, and 46 of tannin. 



A piece of drv calf-skin, perfectly free from extraneous 

 matter, that weighed ISO grains, after being prepared for 

 tannins: by long immersion in water, was tanned m a por- 

 tion of the infusion, being exposed to it for three weeks. 

 When dry, the leather weighed 295 grains ; so that, con- 

 sidering this experiment as accurate, leather quickly tanned 

 by means of an infusion of galls consists of about 61 grains 

 of skin, and 39 of vegetable matter, in 100 grains. 



After depriving a portion of the infusion of all its tanning 

 matter, by repeatedly exposing it to the action of pieces of 

 skin, 1 found that it ,gave a much slighter colour to oxy- 

 genated sulphate of iron than an equal portion of a similar 

 infusion which had been immediately precipitated by solu- 

 tion of isinglass ; but I am inclined to attribute this effect, 

 not to any absorption of gallic acid by the skin, but rather 

 to the decomposition of it by the long continued action of 

 the atmosphere; for much insoluble matter had been pre- 

 cipitated during the process of tanning, and the residuum 

 contained a small portion of acetous acid. 



In ascertaining the quantity of tannin in galls, I found 

 that 500 grains of good Aleppo galls gave, oy lixiviation 

 with pure u ater till their soluble parts were taken up, and 

 subsequent slow evaporation, 185 grains of solid mattcr- 

 And this matter, examined by analysrs, appeared to consist 

 Of tannin _ - - - _ 130 grs. 



Of mucilage, and matter rendered insoluble by 



evaporation - - - - 12 



Of gallic acid, with a little extractive matter - 31 

 Kinialnder, calcareous earth and saline matter 12 

 7J^c HulU obtiiined bv the Ijist lixiviatioii of galls, as 



M. Devcux 



