Commentary Page 151



	THEOPHRASTUS ON STONES

	Crete and Mt. Taygetus in Laconia as well as the distant sources like Armenia, Cilicia, and countries beyond the Alps. There is, however, nothing remarkable about whetstones being brought from a distant place like Armenia, since such stones may have been far superior in quality to those brought from nearer places. At the present day whetstones that have desirable properties and can be obtained only in certain places are often exported to distant markets. 45. The nature of the stone which tests gold is remarkable, for it seems to have the same power as fire, which can test gold too. In this and the two following sections, Theophrastus alludes to the touchstone and its use in testing precious metals. Since these passages contain the earliest account of a method of determining the quantitative composition of an alloy, or, indeed, of a material of any sort, they are of considerable importance in the history of assaying in particular and of analytical chemistry in general. The test of gold by fire is also mentioned by a few other ancient writers. Plato³⁰⁹ apparently alludes to it, and Pliny³¹⁰ states diat fire was used to test gold, and that the purity of the metal was confirmed if it retained its original color after being heated to redness. He adds that the term obrussa was used as the name for the test. In the Leyden Papyrus X the following description of the ancient test by fire is given in recipe 43: A TEST FOR GOLD If you wish (to test) the purity of gold, remelt it or heat it. If it is pure, it keeps the same color and remains pure like coinage after heating. If it appears whiter, it contains silver; if rougher and harder, it contains copper and tin; if black and soft, it contains lead.³¹¹ Pliny³¹² gives details of the fire test as it was applied to silver, and in the Leyden Papyrus X the fire test for silver is described immediately after the one for gold that has just been quoted. It ³⁰⁹ Republic, 413 E. ³¹⁰ XXXIII, 59. ³¹¹ Translated from the text of Berthelot, Archeologie et Histoire des Sciences, pp. 284, 286. ³¹² XXXIII, 127.

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