or STRONTIAN EARTH, a new species of earth lately discovered at Strontian in Scotland.
Who the discoverer of this earth was we have not learned; but Dr Kirwan says, the first information he received of it was from Dr Crawford in the year 1790. In the Miners Journal for February 1791 a good description of its external appearance, with some account of its chemical properties, was published from the observations of Mr Sulzer. Dr Kirwan examined it in October 1793, and found it to be a new earth between the barytic and common limestone. Dr Hope, who is now joint professor of chemistry with Dr Black in the university of Edinburgh, read a paper on the 4th November 1793 before the Royal Society of Edinburgh, intitled "An Account of a Mineral from Strontian, and of a peculiar Species of Earth which it contains;" an abridgment of which is published in the third volume of the Edinburgh Philosophical Transactions. Mr Schmeisser read a paper on the same subject before the Royal Society of London in May 1794, which is published in their Transactions for that year, p. 418, &c.
Its external characters are these: Its colour is whitish or light green; its lustre common; its transparency intermediate between the semitransparent and opaque; its fracture striated, presenting oblong distinct concretions, somewhat uneven and bent; its hardness moderate, being easily scratched, but not scraped. It is very brittle; and its specific gravity from 3.4 to 3.644.
For a full account of its chemical qualities we must refer to the books already mentioned, as all the accounts of it which we have seen are too long to insert here, and as we do not consider the circumstance of its being a newly discovered earth a sufficient reason for running into a tedious detail till its utility be ascertained. We shall, however, mention some of its most remarkable qualities. It requires 180 times its weight of water at a low temperature to dissolve it. When dissolved in boiling water, and allowed to cool, it deposits transparent crystals, which when exposed to the air become white and powdery. It is not affected by the sulphuric acid; but when diluted, 10,000 parts of it will dissolve one of strontites. Diluted nitric acid dissolves it rapidly. The muriatic acid, whether diluted or oxygenated, dissolves it in a similar manner.
Strontites has a strong resemblance to barytes, but essentially differs from it. Its specific gravity is less; it parts with its carbonic acid when urged by heat somewhat more readily, and without suffering fusion; when calcined, it imbues moisture with vastly greater avidity, swelling and cracking with more heat and noise. Strontites dissolves much more abundantly in hot water than barytes; and the form of the crystals of these pure earths is very dissimilar.
The compounds generated by strontites differ from those of barytes. It will suffice to mention the nitrate and muriate. This earth, united to nitric and muriatic acid, forms salts that suffer changes from exposure to air, which do not happen to the nitrate and muriate of barytes. They are likewise much more soluble in water, and have crystals of a peculiar figure. The combinations of strontites with acids are not, like those of barytes, decomposed by prussiate of lime or potash. Strontites and its compounds tinge flame, which barytes does not. Lastly, these earths dilate in the order of their attractions. From these considerations it is concluded, that the mineral is not aerated barytes.
It also is distinguished from calcareous spar or limestone: for it is much heavier, and retains its fixed air with more obstinacy in the fire. The incomparably greater solubility of the pure earth in hot than in cold water, and the crystalline form it assumes, sufficiently distinguish it from lime, which the deposition of the nitrate and muriate to crystallize no less tends to do.
The most remarkable quality of strontites is that of tingling flame of a red colour. The muriate has it in the most eminent degree, and its effects are well exhibited by putting a portion of the salt on the wick of a candle, which is thereby made to burn with a very beautiful blood-red flame. The nitrate stands next, then crystallized strontites, and after it the acetate. A hundred parts of strontites are composed of 61.21 of earth, 30.20 of carbonic acid, and 8.59 of water.