Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/369

 Haüy. I have however been able to perceive only a simple refraction in this substance.

C. Chemical.

Action of acidss. None, when the bardiglione is pure.

Action if Heat. A moderate degree of heat renders such of its varieties as are indeterminate of a dull white colour; but has no such effect on those that are crystallized; yet when the crystalline variety of the salt-works of Bex, enclosed in a mass of compact bardiglione mixed with gypsum and sea-salt, is exposed to heat, it gives both to its crystal and to their fragments whitish tint, frequently accompanied with a pearly lustre.

When the heat of the blowpipe is applied to the thin edges of this substance, it appeared to me to act in the same manner as it does on gypsum: the bardiglione passing, without any ebullition, into a very friable white enamel. The resistance of this substance to fusion, when tried on large pieces, added to the friability of the enamel, is no doubt the reason why several mineralogists have said it was infusible by the blowpipe; but if its action be applied, as I have mentioned, to the thin edges, their blistered appearance instantly demonstrates its fusibility.

Analysis. In the first analysis of bardiglione, Klaproth found 15 parts of sea-salt, 27 of gypsum, and 58 of sand; but the specimen analysed by him must certainly have been very impure. Vauquelin, after having freed it from the sea-salt, which is foreign to its composition, found it to consist of 40 parts of lime and 69 of sulphuric acid.