Page:Proceedings of the Royal Society of London Vol 1.djvu/241

Rh portion of a grayish-black substance was produced, which was highly inﬂammable, was easily melted, and was readily dissolved in cold alcohol; from which. like the resins,_ it might be precipitated by water.

From coagulated albumen, and from prepared muscular ﬁbre, nothing but coal could be obtained.

In the above experiments there appeared to be a certain period of the process when the production of the tanning substance arrived at its maximum; after which a gradual diminution, and at length a total destruction of it, took place, and it became mere coal.

Some experiments are now related, made with nitric acid, on the elastic bitumen, and on several kinds of coal. The result was, that from elastic bitumen, common pit-coal, Cannel—coal, and asphaltum, there was obtained, not only the taming substance, but also another substance, which possessed properties intermediate between those of resin and those of vegetable extractive matter; but this substance might, by digestion in nitric acid, be converted into the tanning sub- stance. From Kilkenny—coal, and from two other kinds of coal, one from Wales, the other from North America, none of the above-men- tioned resinous substances were obtained.

hir. Hatchett now proceeds to mention a variety of experiments made on horse-chestnuts, and on their peels. From these it appeared, that the small portion of tannin originally contained in horse-chest- nut peels is destroyed by the process of roasting; but that the brown decoctions of the roasted horse-chestnuts, and of their peels, might be made to afford the tannin matter, by the addition of nitric acid. The above brown decoctions appeared to contain carbon, combined with oxygen, sufﬁcient to give it many of the pr0perties of coal; but the compound is nevertheless capable of being dissolved by water with great facility.

Solutions similar to the above may, our author thinks, he obtained whenever vegetable matter undergoes the putrefactive process, as in dunghills, 8m. He examined the brown liquor that runs from walnut- peels when kept in a heap for a certain time, and found that, like the decoctions above mentioned, it contained carbon in a state ap- proaching to coal, and that, by the addition of nitric acid, a small portion of the tanning substance might be procured from it.

Some experiments were likewise made upon galls ; the results of which showed, that the natural tannin contained in them is destroyed by nitric acid; that it is also diminished, and ultimately destroyed, by roasting; but when the galls have not been so much roasted as to destroy the whole of the tannin, the remainder of that substance is destroyed by the addition of nitric acid, whilst, at the same time, a small portion of the artiﬁcial tannin is produced.

Results nearly similar were obtained from experiments upon oakbark; and it also appeared, that when that bark was exhausted of its natural tannin, it might, by roasting and being treated with nitric acid, be made to yield the artiﬁcial tanning substance. This process was several times repeated upon the same portion of bark; and as it