43. Chap. 43.-Touchstones For Testing Gold.

CHAP. 43.—TOUCHSTONES FOR TESTING GOLD.

A description of gold and silver is necessarily accompanied by that of the stone known as "coticula."[1] In former times, according to Theophrastus, this stone was nowhere to be found, except in the river Tmolus,[2] 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[3] 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.

1. Literally "whetstone." He is speaking of the stone known to us as Touchstone, Lydian stone, or Basanite—"a velvet-black siliceous stone or flinty jasper, used on account of its hardness and black colour for trying the purity of the precious metals. The colour left on the stone after rubbing the metal across it, indicates to the experienced eye the amount of the alloy." —Dana, Syst. Mineral. p. 242.

2. In Lydia. See B. v. cc. 30, 31.

3. As a test. At the present day, concentrated nitric acid is dropped on the mark left by the metal; and the more readily the mark is effaced, the less pure is the metal.