Page:Proceedings of the Royal Society of London Vol 1.djvu/243

Rh only remark, that a much greater proportion of coal is obtained from those substances by means of the above acid than can .be obtained by distillation.

Two experiments on the humid formation of coal are also de« scribed: from one of these it appears that oak-wood may, by sul- phuric acid, be converted into a coal which is very diﬁ'erent from charcoal, and which, by its mode of burning, and by its not affording any alkali, resembles those mineral coals that do not contain bitu- men.

The other experiment shows that oak-wood may also be converted into a sort of coal by muriatic acid; but this coal retains some vege- table characters, although no alkali can be obtained from its ashes..

Mr. Hatchett now proceeds to make some remarks on the natural formation of coal. After stating the various theories that have been formed on that subject, he considers as the most probable the theory which ascribes the principal origin of coal to vegetable substances ; that idea of its origin being, he says, corroboratedby the greater number of geological facts. The observations, however, that haver been made upon the submerged wood found at Sutton and other places, show, our author thinks, that vegetable substances, buried under the sea or under the earth, are not, merely by such means; converted even into the most imperfect sort of coal; some other process being evidently necessary to produce this change, which in a former paper he endeavoured to demonstrate to be progressive.

That some sorts of coal are of vegetable origin, there cannot, lVIr. Hatchett says, be any doubt: several of them, as the Bovey coal, the Sussex coal, the surturbrand, &c. not only still retain some of their external vegetable characters, but also yield resin,—a substance allowed to belong exclusively to organized natural bodies. Some mineralogists, however, have attempted to distinguish the above- mentioned coals from others, which they denominate True Mineral Coals: but it has in the former part of this paper been shown, that when pit—coal, Cannel-coal, and asphaltum, (which are considered as of mineral origin,) are subjected to the action of nitric acid, and the process i stopped at a proper period, there remains a substance which is intermediate between resin and vegetable extractive matter: It has also been stated, that, by similar means, a substance possessing nearly the same properties may be obtained from the known vegetable resms.

Our author indeed admits that bitumen has never been formed by any artiﬁcial process, and that he has himself attempted it, in various ways, without success: yet we may conclude, from what has been already said, that bitumen is a modiﬁcation of the resinous and oily parts of vegetables, produced by some process of nature, operated by gradual means on immense masses; and we have, he thinks, great reason to conclude that the agent employed by nature in the formation of coal and bitumen is either the muriatic or the sulphuric acid. Common salt, however, is never found in coal-mines, except when they are in the vicinity of salt-springs ; whilst, on the contrary, py-