_Touchstone_ (Vol. vii., p. 82.).--I think your correspondent ALPHAGE is
mistaken in alleging that the word _touchstone_ is so called because it
"gives a musical sound when touched with a stick."
The _touchstone_ is the dark-coloured flinty slate or schistus (the _Lapis
Lydius_ of the ancients), which has been used from the remotest ages, down
even to our own days, for testing gold. By touching the black stone with
the metal, it leaves behind a clear mark, the colour of which indicates the
distinction between the pure and alloyed. Pliny describes it (lib. xxxiii.
cap. 43.):
"Auri argentique mentionem comitatur lapis quem coticulam appellant,
quondam non solitus inveniri, nisi in flumine Tmolo, ut auctor est
Theophrastus: nunc vero passim; quem alii Heraclium, alii Lydium
vocant. His coticulis periti, cum e vena ut lima rapuerint
experimentum, protinus dicunt quantum auri sit in ea, quantum argenti
vel æris, scripulari differentia, mirabili ratione, non fallente."
This is the substance referred to in the apothegms of Lord Bacon, that
"gold is tried by the _touchstone_, and men by gold."
The French, from the same practice, know the same substance by the name of
_Pierre de touche_. The use of the touchstone, at the present day, is thus
described by Ure in his _Dictionary of Arts and Mines_, under the head of
"Assay:"
"In such small work as cannot be assayed, by scraping off a part and
cupelling it, the assayers endeavor to ascertain its fineness or
quality by the touch. This is a method of comparing the colour and
other properties of a minute portion of the metal, with those of small
bars, the composition of which is known. These bars are called _touch
needles_, and they are rubbed upon a smooth piece of black basaltes, or
pottery, which _for this reason is called the touchstone_."