As it is a fact generally admitted, that minium is a poison,[1034] I look upon all the recipes given as highly dangerous which recommend its employment for medicinal purposes; with the exception, perhaps, of those cases in which it is applied to the head or abdomen, for the purpose of arresting hæmorrhage, due care being taken that it is not allowed to penetrate to the viscera, or to touch any sore. Beyond such cases as these, for my own part, I should never recommend it to be used in medicine. CHAP. 42.—THE METHOD OF GILDING SILVER. At the present day silver is gilded almost exclusively by the agency of hydrargyros;[1035] and a similar method should always be employed in laying gold leaf upon copper. But the same fraud which ever shows itself so extremely ingenious in all departments of human industry, has devised a plan of substituting an inferior material, as already mentioned.[1036] CHAP. 43.—TOUCHSTONES FOR TESTING GOLD. A description of gold and silver is necessarily accompanied by that of the stone known as “coticula.”[1037] In former times, according to Theophrastus, this stone was nowhere to be found, except in the river Tmolus,[1038] but at the present day it is found in numerous places. By some persons it is known as the “Heraclian,” and by others as the “Lydian” stone. It is found in pieces of moderate size, and never exceeding four inches in length by two in breadth. The side that has lain facing the sun is superior[1039] to that which has lain next to the ground. Persons of experience in these matters, when they have scraped a particle off the ore with this stone, as with a file, can tell in a moment the proportion of gold there is in it, how much silver, or how much copper; and this to a scruple, their accuracy being so marvellous that they are never mistaken. CHAP. 44.—THE DIFFERENT KINDS OF SILVER, AND THE MODES OF TESTING IT. There are two kinds of silver. On placing a piece of it upon an iron fire-shovel at a white heat, if the metal remains perfectly white, it is of the best quality: if again it turns of a reddish colour, it is inferior; but if it becomes black, it is worthless. Fraud, however, has devised means of stultifying this test even; for by keeping the shovel immersed in men’s urine, the piece of silver absorbs it as it burns, and so displays a fictitious whiteness. There is also a kind of test with reference to polished silver: when the human breath comes in contact with it, it should immediately be covered with steam,[1040] the cloudiness disappearing at once. CHAP. 45. (9.)—MIRRORS.