Page:Proceedings of the Royal Society of London Vol 1.djvu/108

Rh Next follow the tables of the contents of six kinds of corundum, viz. the sapphire, the ruby, and the corundum from the Camatic, from Malabar, from China, and from Ava. The proportions of the ﬁrst species are 5¼ silica, 92 alumina, 1 iron, and 1¾ loss. The proportions of the other kinds do not differ very considerably from these.

The matrices of these stones being more easily fused than the six kinds above mentioned, the usual and well known mode of treatment by potash was found sufﬁcient to render them soluble in acids. Although this mode be now very familiar to chemists, the author, however, in order to leave no cause for suspicion, describes the process he used with the matrix of the corundum from the peninsula of India. The results gave 42½ silica, 37½ alumina, 15 lime, 3 iron, and 2 loss, with a trace of manganese. By similar treatment the various substances contained in this and some other matrices, viz. felspar, fibrolite, and three sorts of thallite, were analysed, and the results are given in tables. It is remarkable that while all the other substances yield in different proportions the same ingredients as the matrices themselves, the ﬁbrolite was found to consist only of silica and alumina, the quantity of iron it contained being so small as hardly to deserve notice.

In the prosecution of this inquiry Mr. Chenevix observed, that if a quantity of potash be for some time kept in fusion in a platina crucible, the latter will be found to lose some grains of its weight. The quantity of the metal thus lost he actually found in the potash: and hence he infers the afﬁnity between these two substances, which afﬁnity, it seems, is made use of by the Spaniards for detecting the platina contained in the ingots of gold sent from their American possessions. He also has occasion to show that potash which has usually been denominated a ﬁxed alkali is not so, strictly speaking, since there is a degree of heat by which it may be totally volatilized.

In a second part of the paper the author treats of the affinities which the earths are supposed to exercise towards each other When held in solution by acid or alkaline menstrua. There being a difference of opinion on this subject among some of the most eminent chemists, Mr. Chenevix has repeated many of their experiments, especially those of Guyton de Morveau. After descanting largely on the probable causes of error in this eminent chemist, as well as in Mr. Kirwan and others, he derives from his results the following general conclusions.

1st. That there exists an afﬁnity between silica and alumina.

2ndly. That there exists a very powerful afﬁnity between alumina and magnesia.

3rdly. That alumina shows an afﬁnity for lime.

4thly. That Mr. Guyton was mistaken in every instance of afﬁnity between the earths, except in one which had been observed before his experiments; and that he has attributed to a cause which does not exist, phænomena that must have resulted from the impurity of his re-agents.

And lastly, That neither the experiments of Mr. Guyton, nor an