gold-silver alloys that have a favorable range of composition, and it cannot be obtained on gold-copper alloys of any range of composition. Only under the most favorable conditions, including the use of reagents, is it possible to reach or exceed the degree of delicacy claimed by Theophrastus for the touchstone method of assaying. It is said to be possible under such conditions to estimate the gold content of alloys that are between 700 and 800 fine (70 to 80 per cent of gold) to within 1 part in 200:328 The ancients were probably able to determine differences in composition represented by the other weights named by Theophrastus when the method was applied to gold alloys. It is especially interesting to note that, when the stater is taken as the standard, the two largest weights, the tetartemorion and the hemi-obolos, correspond to the half-carat and the carat, which are used on the present English and American commercial scale to express the quality of gold alloys. It is obvious, therefore, that by means of the weight scale given by Theophrastus, the ancient Greeks could have expressed the composition of their gold alloys in much the same way as it is done today.
For silver, the touchstone method of assaying is considerably less delicate than for gold, though Professor Gowland329 shows that a skillful assayer can determine the proportion of the metals in a rich alloy of silver and copper to within 1.5 or 2 parts in 100. However, alloys poor in silver or very rich in it cannot be assayed with even this degree of accuracy. It is clear, therefore, that no difference in composition smaller than that represented by the tetartemorion could have been determined by the ancients when they were assaying silver alloys with the touchstone, and it is likely that the method was frequently not sufficiently delicate to measure difference in composition smaller than that represented by the hemiobolos when the stater was taken as the standard.
47. All such stones are found in the river Tmolos. No river of this name is mentioned by ancient writers on geography. Strabo330 applies the name to die mountain in Lydia lying between the river Hermos on the north and the Kaystros or
328 Τ. Κ. Rose, Metallurgy of Gold (London, 1915), p. 554.
329 Journal of the Institute of Metals, IV (1910), 13. 330XIII, 4, 5 and 12-13.
