This section is from the book "An Experimental History Of The Materia Medica", by William Lewis.
Lapis CaeRuleus; Lapis cyanus; Caeru-leum nativum. Lapis lazuli: a compact ponderous soffil; less hard than slint; of a deep blue colour, variegated commonly with gold or silver coloured points or veins; retaining its colour in a moderately strong fire, in a very strong one calcining to a brown, and at length melting into a dusky coloured glass with bluish clouds; losing its colour, and in great part dissolving, by digestion in mineral acids; said to be found in the mines of gold, silver, and copper, in the eastern countries and in somc parts of Germany (a).
This stone, levigated into an impalpable powder, and freed from the groser parts by washning with water, has been given in doses of half a dram and a dram, and said to operate strongly by stool and vomit. Some have recommended it in epilepsies and intermitting severs: Dolaeus tells us, that in this last dis-order, the above doses, taken on the approach of a fit, with two or three spoonfuls of brandy, were with him a singular secret. The ancients supposed, that it evacuates chiefly what they called melancholic humours or adust black bile, probably, as Geoffroy suspects, on account of its tinging the feces black; a property, from which it may rather be prefumed that the mineral participates of iron. The constringing power, which is likewise ascribed to it, depends perhaps on this ingredient; but neither its real medical qualities, nor its chemical composition, are as yet known. Its ferrugineous impregnation is apparent, from its yielding yellow martial flowers on sublimation with sal ammoniac, and from solu-tions of it in mineral acids affording a blue precipitate with the tincture of Prussian blue de-scribed under the article serrum. It has been generally supposed to participate pretty largely of copper; but pure lapis lazuli gives no mark of copper; and those, who speak of experiments discovering that metal in it(a), have probably taken for lapis lazuli some other blue stones, as the lapis armenus, which plainly contains copper, and which some celebrated naturalists have ranked as a species of the lazuli. The lapis armenus may be readily diftinguished, by its being less hard than the lazuli, soon losing its blue colour in moderate fire, and raising an effervefcence with acids, its basis seeming to be a calcareous earth.
(a) See Cronftedt's mineral system, and Marggras's chemical works.