126                 NATURAL HISTORY OF GEMS.
	sole use in medicine is for promoting the growth of hair, especially of the eyelashes " (xxxv. 28). But by a curious oversight Pliny has (xxxiii. 57) applied the exact words of the remainder of the same chapter of Theophrastus, describing the Cyanos, to his paint, Cœru-leum, for, after stating that it is found in silver-mines in the form of sand, he adds: " Of old time there were three kinds of it,—the Egyptian the most esteemed ; the Scythian; this is easily dissolved, and in grinding up divides itseli into four shades—a lighter, a darker, a thicker and a thinner—to the latter the Cyprian is even now preferred. To these are newly added the Spanish, and that from Pute-oli, for they have begun to manufacture it in those places. It is all, however, stained and boiled with a peculiar plant until it imbibes the colour : afterwards it is treated like the Chrysocolla. The test of the purity of Cœruleum is for it to blaze if thrown upon hot coals ; the false kind is made by mixing the water in which dried violets have been boiled with Eretrian chalk. The effect of Cajruleum in medicine is to cleanse ulcers, on which account it enters into the composition of certain ointments." All which notices go to prove that the base of the several blues of the Romans was Sulphate of Copper under various forms. And to sum up : both kiwqs and Cœruleum aro nothing more than literal translations of the Persian Azul, " blue : " a mere epithet of colour.