phrastus in the next section and those made by Pliny316 show clearly that the ancients achieved results in the use of the touchstone that approached in delicacy those obtained at the present time. Since the references made by ancient authors to the touchstone and its uses show that they had no direct knowledge of the method of performing the test, it is not surprising that no mention is made by them of any standards of comparison. It is very improbable that the ancients made this method of assaying more reliable by the use of chemical reagents, since the principal reagents that are necessary, namely, nitric acid and aqua regia, were almost certainly unknown to them. It is of considerable interest to note that the method of testing gold and gold alloys by the touchstone is still very widely used at the present time, especially by jewelers and by dealers in scrap gold.
Silver and silver alloys may also be tested by the touchstone, though the method is less suitable for silver than for gold. Theophrastus shows in the next section that the ancients did use the touchstone for testing silver. Although it was also used in early modern times for assaying the alloys of silver and copper, as is shown by the detailed descriptions of the process in various early works on assaying,317 the method is no longer employed for the quantitative testing of silver alloys. It is still used, however, by jewelers and by dealers in precious metals to detect silver in various alloys, and appropriate reagents are applied to the streak left on the stone by the alloy of unknown composition. In the earlier use of the touchstone for assaying alloys of silver and copper, graded touch needles composed of alloys of silver and copper were employed, and the streak left on the stone by the unknown alloy was compared with those left by the standard alloys.
46. They say that a much better stone has now been found than the one used before; for this not only detects purified gold, but also gold and silver that are alloyed with copper, and it shows how much is mixed in each stater. Probably the touchstone was first used only in a qualitative way
sle XXXIII, 126.
317 E.g., J. Pettus, The Laws of Art and Nature in Knowing, Judging, Assaying, Fining, Refining, and lnlarging the Bodies of confin'd Metals (London, 1683), PP· 63"<>5.
