205 



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 

 off 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 the.-i 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. 



Additional Experiments and Remarks on an artificial Substance, which 

 possesses the principal characteristic Properties of Tannin. By 

 Charles Hatchett, Esq. F.R.S. Read June 27, 1805. [Phil. Trans. 

 1805,;?. 285.] 



Mr. Hatchett was, he says, at first 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 effect of nitric acid (which 

 acid produces the one while it destroys the other), he thought it ne- 

 cessary to make some experiment? on the comparative effects 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 difficulty. 



Muriatic acid also, appeared to have no effect on this substance ; 

 and Mr. Hatchett remarks, that the solutions of it seem to be com- 

 pletely imputrescible, also, that they do not become mouldy, like the 

 infusions of galls, sumach, &c. 



Some comparative experiments were then made, by means of ni- 

 tric acid, on galls, sumach, Pegu 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 effects of nitric acid much more than galls, sumach, kascutti, 

 and Pegu cutch. 



A number of miscellaneous experiments on the substance here 



