touchstone

touchstone
/tuch"stohn'/, n.
1. a test or criterion for the qualities of a thing.
2. a black siliceous stone formerly used to test the purity of gold and silver by the color of the streak produced on it by rubbing it with either metal.
[1475-85; TOUCH + STONE]
Syn. 1. standard, measure, model, pattern.

* * *

Black, silica-containing stone used in assaying to determine the purity of gold and silver.

The metal to be assayed is rubbed on the touchstone, and then a sample of metal of known purity is rubbed on the stone right next to it. The streaks of metal on the stone are treated with nitric acid, which dissolves impurities, thus increasing the contrast between the two samples when compared. Because other metals, such as copper, can be alloyed to silver without changing its colour significantly, the touchstone method is not usually used now to assay silver, though it is still used to assay gold and provides a reasonably accurate guide to quality.

* * *

      black siliceous stone used to ascertain the purity of gold and silver. assaying by “touch” was one of the earliest methods employed to assess the quality of precious metals. The metal to be assayed is rubbed on the touchstone, adjacent to the rubbing on the touchstone of a sample of a metal of known purity. The streaks of metal left behind on the touchstone are then treated with nitric acid, which dissolves impurities, and thus, when the streaks are compared, the contrast between pure and impure metal is heightened. Because other metals, such as copper, can be alloyed to silver without significantly changing its colour, the touchstone method is not usually employed now to assay silver. It is still used, however, to assay gold and provides a reasonably accurate guide to quality.

* * *


Universalium. 2010.

Игры ⚽ Нужен реферат?
Synonyms:

Look at other dictionaries:

  • Touchstone — Pictures (engl. touchstone = „Prüfstein”), auch bekannt als Touchstone Films, ist eine US amerikanische Filmproduktionsfirma mit Firmensitz in Burbank, Kalifornien, die zur Walt Disney Company gehört. Inhaltsverzeichnis 1 Firmengeschichte 2… …   Deutsch Wikipedia

  • Touchstone — Touch stone , n. 1. (Min.) Lydian stone; basanite; so called because used to test the purity of gold and silver by the streak which is left upon the stone when it is rubbed by the metal. See {Basanite}. [1913 Webster] 2. Fig.: Any test or… …   The Collaborative International Dictionary of English

  • TouchStone — is a 1980s rock band out of Vienna, Austria. The group was made up of founding member and singer/song writer Dain Turner, guitarist Hossein Yasery Manesh, keyboardist Christian Skokan, bassist Günter Kopler, and drummer Alfred Vollbauer. In 1982… …   Wikipedia

  • touchstone — index standard Burton s Legal Thesaurus. William C. Burton. 2006 …   Law dictionary

  • touchstone — (n.) late 15c., from TOUCH (Cf. touch) (v.) + STONE (Cf. stone) (n.). Black quartz, used for testing the quality of gold and silver alloys by the color of the streak made by rubbing them on it. Cf. also BASALT (Cf. basalt). Figurative sense is… …   Etymology dictionary

  • touchstone — *criterion, *standard, gauge, yardstick Analogous words: test, proof, trial, demonstration (see under PROVE) …   New Dictionary of Synonyms

  • touchstone — ► NOUN 1) a piece of fine grained dark schist or jasper formerly used for testing alloys of gold by observing the colour of the mark which they made on it. 2) a standard or criterion …   English terms dictionary

  • touchstone — [tuch′stōn΄] n. 1. a type of black stone formerly used to test the purity of gold or silver by the streak left on it when it was rubbed with the metal 2. any test of genuineness or value …   English World dictionary

  • Touchstone — A touchstone is a small tablet of dark stone such as fieldstone, slate, or lydite, used for assaying precious metal alloys. It has a finely grained surface on which soft metals leave a visible trace.Probing with a touchstoneBy rubbing a metal on… …   Wikipedia

  • Touchstone — Cette page d’homonymie répertorie les différents sujets et articles partageant un même nom. Touchstone peut désigner: Le studio de cinéma Touchstone Pictures La filiale télévision de ce studio Touchstone Television renommé ABC Television Studio… …   Wikipédia en Français

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”