Note note 37, p. 252 — BOOK VII.

[Pg 252][37] Historical Note on Touchstone. (Coticula. Interpretatio,—Goldstein). Theophrastus is, we believe, the first to describe the touchstone, although it was generally known to the Greeks, as is evidenced by the metaphors of many of the poets,—Pindar, Theognis, Euripides, etc. The general knowledge of the constituents of alloys which is implied, raises the question as to whether the Greeks did not know a great deal more about parting metals, than has been attributed to them. Theophrastus says (78-80): "The nature of the stone which tries gold is also very wonderful, as it seems to have the same power with fire; which is also a test of that metal. Some people have for this reason questioned the truth of this power in the stone, but their doubts are ill-founded, for this trial is not of the same nature or made in the same manner as the other. The trial by fire is by the colour and by the quantity lost by it; but that by the stone is made only by rubbing the metal on it; the stone seeming to have the power to receive separately the distinct particles of different metals. It is said also that there is a much better kind of this stone now found out, than that which was formerly used; insomuch that it now serves not only for the trial of refined gold, but also of copper or silver coloured with gold; and shows how much of the adulterating matter by weight is mixed with gold; this has signs which it yields from the smallest weight of the adulterating matter, which is a grain, from thence a colybus, and thence a quadrans or semi-obolus, by which it is easy to distinguish if, and in what degree, that metal is adulterated. All these stones are found in the River Tmolus; their texture is smooth and like that of pebbles; their figure broad, not round; and their bigness twice that of the common larger sort of pebbles. In their use in the trial of metals there is a difference in power between their upper surface, which has lain toward the sun, and their under, which has been to the earth; the upper performing its office the more nicely; and this is consonant to reason, as the upper part is dryer; for the humidity of the other surface hinders its receiving so well the particles of metals; for the same reason also it does not perform its office as well in hot weather as in colder, for in the hot it emits a kind of humidity out of its substance, which runs all over it. This hinders the metalline particles from adhering perfectly, and makes mistakes in the trials. This exudation of a humid matter is also common to many other stones, among others, to those of which statues are made; and this has been looked on as peculiar to the statue." (Based on [Pg 253]Hill's trans.) This humid "exudation of fine-grained stones in summer" would not sound abnormal if it were called condensation. Pliny (XXXIII, 43) says: "The mention of gold and silver should be accompanied by that of the stone called coticula. Formerly, according to Theophrastus, it was only to be found in the river Tmolus but now found in many parts, it was found in small pieces never over four inches long by two broad. That side which lay toward the sun is better than that toward the ground. Those experienced with the coticula when they rub ore (vena) with it, can at once say how much gold it contains, how much silver or copper. This method is so accurate that they do not mistake it to a scruple." This purported use for determining values of ore is of about Pliny's average accuracy. The first detailed account of touch-needles and their manner of making, which we have been able to find, is that of the Probierbüchlein (1527? see Appendix) where many of the tables given by Agricola may be found.