Chap. 44.] THE DIFFERENT KINDS OF SILVER. 125 



plan of substituting an inferior material, as already men- 

 tioned. 84 



CHAP. 43. TOUCHSTONES FOR TESTING GOLD. 



A description of gold and silver is necessarily accompanied 

 by that of the stone known as " coticula." 8 * In former times, 

 according to Theophrastus, this stone was nowhere to be 

 found, except in the river Tinolus, 86 but at the present day it is 

 found in numerous places. By some persons it is known as 

 the " Hcraclian," 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 lias lain 

 facing the sun is superior* 7 to that which has lain next to the 

 ground. Persons of experience in these matters, when they 

 have scraped a particle oil' 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 mis- 

 taken. 



CHAT. 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 lictitious whiteness. There is also a kind of test with 

 reference to polished silver : when the human breath comes 



81 In Chapter 32. He alludes to the use of glair of ejrgs. 



w 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 rub- 

 bing the metal across it, indicates to the experienced eye' the amount of 

 the alloy." Dana, Svst. Mineral, p. 242. 



66 Ju'Lydia. See li. v. cc. 30, 31. 



h7 As a test. At the present day, concentrated nitric acid is dropped rn 

 the mark left by thr metal ; and the more readily the mark is effaced, the 

 less pure is the metal. 



