I said before, that siliceous earth combinedwith no acid but the fluoric; it is for this reasonthat glass is liable to be attacked by that acidonly, which, from its strong affinity for silex,forces that substance from its combination withthe potash, and thus destroys the glass.

We will now hasten to proceed to the otherearths, for I am rather apprehensive of yourgrowing weary of this part of our subject.

CAROLINE.

The history of the earths is not quite so enter-taining as that of the other simple substances.

MRS. B.

Perhaps not; but it is absolutely indispensablethat you should know something of them ; forthey form the basis of so many interesting and im-portant compounds, that their total omissionwould throw great obscurity on our general out-line of chemical science. We shall, however,review' them in as cursory a manner as the sub-ject can admit of.

Ale mine derives its name from a compoundsalt called alum, of which it forms the basis.

CAROLINE.

But it ought to be just the contrary, Mrs. B.—;