Page:Proceedings of the Royal Society of London Vol 1.djvu/225

Rh the oxide. than dry wood, coal, or sulphur. A single grain of cam: phor, dissolved in an adequate portion of alcohol, was found sufﬁ- cient, when assisted by a red heat. to render all the particles of 100 grains of the oxide magnetic. But such substances as are easily sub- limed. will, by a continued application even of a low heat, quit the oxide, leaving it, as at ﬁrst, unmagnetic. Hence we may understand why Prussian blue, sulphurets, and ores of iron, containing inﬂam- mable matter, become magnetic by the agency of heat, and revert to their unmagnetic state if the heat is continued long enough to drive 03 the inﬂammable matter.

The intention of this paper, Mr. Lane says, is to prove that mere oxides of iron are not magnetic; that inﬂammable substances do not render them magnetic until such substances are, by heat, chemically combined with them; and that when the combustible substance is again separated by heat, the oxides return to their unmagnetic state.

Mr. Hatchett was, he says, at fust inclined to consider the arti- ﬁcial tanning product as exactly similar to the natural vegetable prin— ciple called tannin; but as there appeared to be a considerable dif- ference between them with respect to the eﬂ'ect of nitric acid (which acid produces the one while it destroys the other), he thought it ne- cessary to make some experiments on the comparative elfects of this acid on those substances which contain the largest proportions of tannin.

He accordingly subjected the artiﬁcial product, sometimes alone, and sometimes mixed with other substances, to the action of nitric acid; and although Mr. Hatchett cannot, he says, assert that this substance is absolutely indestructible when repeatedly distilled with that acid, yet the results of his experiments showed that the de. struction of it, by that means, would be a work of considerable time and diﬂiculty.

Muriatic acid also, appeared to have no elfect on this substance; and Mr. Hatchett remarks, that the solutions of it seem to be com- pletely imputrescible, also, that they do not become monldy, like the infusions of galls, snmach, 8w.

Some comparative experiments were then made, by means of ni- tric acid, on galls, sumach. Pegn cutch, kascutti, common cutch, and oak-bark; from which it appeared, that although the artiﬁcial pro- duct is by much the most indestructible of all the tanning substances. yet there is some difference in that respect between the various kinds of natural tannin; common cutch and the tannin of oak-bark resist- ing the elfects of nitric acid much more than galls, sumach, kascutti. and Pegu cutch.

A number of miscellaneous experiments on the substance here