Page:Proceedings of the Royal Society of London Vol 1.djvu/107

Rh fragments of quartz, felspar, calcareous spar, a brownish-yellow mica, and particles of attractable oxide of iron.

The paper closes with some account of corundum, which, contrary to the received opinion, that this stone was only found in the East Indies, has been thought to exist in other parts of the world. The author dwells mostly upon the appearances of a stone he himself dis- covered in the mountainous parts of the Forez in France, and which the Abbé Hauy considers only as a species of felspar. The Count al- leges his reasons for classing it with the perfect blue corundum, known by the name of Sapphire. As to various stones found in Germany, in the Isle of Tirree on the western coast of Scotland, on Chesnut-hill near Philadelphia, and elsewhere, which have by some been considered as corundum, the author cautions us against acqui- esciug in those assertions till more conclusive arguments shall appear in their favour.

After a detail of several unsuccessful attempts to analyse this stone, which on account of its great hardness is both diﬂicult to pulverize and to be reduced by saline agents, we ﬁnd an ample description of the process, which was attended with the desired success. A piece of corundum, weighing 100 grains, Was made several times red hot, and plunged into cold water; it was then pounded, ﬁrst in a steel. and next in an agate mortar, and thus reduced into an impalpable powder. This powder was by means of dilute muriatic acid cleared from the ferruginous particles which adhered to it from the steel mortar. It was then put into a platina crucible with 200 grains of sub-horate of soda, and the mixture was exposed for anhour or two to a violent heat: the glass produced by this fusion was in about twelve hours dissolved, by boiling it in a proper quantity of muriatic acid.

The silica might now have been separated by evaporating the whole to dryness, but it was thought preferable to get rid of all the salts contained in the liquor by a precipitation effected by means of an alkaline carbonate. The precipitate thus obtained was then re- dissolved in muriatic acid, and the silica was hence cleared by eva- poration. The remaining liquor was afterwards boiled with potash, by which means the alumina was precipitated. It was then redis! solved by the excess of potash, from which the ea1th was ﬁnally ob- tained by muriate of ammonia. A small proportion of iron was se- parated by muriatic acid. Both these earths being now washed and dried, were ignited, and thus the exact weight of each was accurately ascertained. The author paid particular attention to the silica pro- duced in this process; as Mr. Klaproth, who had formerly analysed this stone, declares that he never found any of this ingredient.