Page:Proceedings of the Royal Society of London Vol 1.djvu/226

Rh treated of are then described, of which we shall only mention one, made to show the effects of heat upon it.

Twenty grains of the substance, prepared by means of nitric acid from pure vegetable charcoal, were subjected to a high degree of heat in a glass retort. A small quantity of nitric acid, from which the substance had not been entirely freed, ﬁrst came over; after this a considerable quantity of ammonia was suddenly produced, which was succeeded by carbonic acid and a small quantity of nitrogen gas. A bulky coal, weighing 8% grains, remained, which, by incineration, yielded 1% grain of brownish white ashes, consisting principally of lime.

Mr. Hatchett now relates an experiment made with indigo, by which he ascertained, that a variety of the vegetable tanning sub- stance might be formed without previously converting the vegetable body into coal; and he has, he says, since discovered, that although indigo yields this substance more readily than most other vegetable bodies, yet very few of those bodies are to be considered as excep- tions. He had in his former paper stated, that in his experiments upon common resin it was necessary to develope part of the carbon in the state of coal by sulphuric acid, in order to produce the tanning substance ; but he has since found, that when the abstraction of ni- tric acid was several times repeated, that substance might be ob- tained not only from common resin, but also from several other re- sinous bodies.

In the course of these experiments Mr. Hatchett found, that by treating dragon's blood with nitric acid, a feather—like sublimate was produced, which had the aspect, odour, and properties of benzoic acid, although no vestige of this acid could be obtained by simply exposing the dragon’s blood to heat. Guaiacum, although similar in its general character to resins, when treated as above, yielded only slight vestiges of the tanning product, but, like the gums, afforded a large quantity of oxalic acid.

In the following section Mr. Hatchett observes, that the decoctions of several roasted vegetable substances did not afford any precipitate with a solution of isinglas; even a decoction of coﬁee did not afford a precipitate until several hours had elapsed; but by adding a small quantity of nitric acid to any of the above decoctions, the tanning substance might be procured from them.

Lastly, the author describes some experiments made by him in order to procure the tanning substance from camphor. For this purpose 100 grains of camphor were dissolved in sulphuric acid, and, after four days, at which time the production of sulphureous acid gas had nearly ceased, cold water was added, and the whole was subjected to distillation; by this, about 3 grains of an essential oil were obtained; and as by a second distillation with water no more essential oil came over, the residuum was treated with successive portions of alcohol until that solvent ceased to act upon it. The residuum had now the appearance of a compact coal, and after desiccation weighed 53 grains. The solution formed by alcohol, upon being