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| [[File:lighterstill.jpg]][[File:Lake-shelbyville-illinois-touchstone-energy-balloon-fest.jpg|right|frame]] | | [[File:lighterstill.jpg]][[File:Lake-shelbyville-illinois-touchstone-energy-balloon-fest.jpg|right|frame]] |
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− | *[http://en.wikipedia.org/wiki/16th_century 1530] | + | *[https://en.wikipedia.org/wiki/16th_century 1530] |
| ==Definitions== | | ==Definitions== |
| *1: a black siliceous stone related to flint and formerly used to test the [[purity]] of gold and silver by the streak left on the stone when rubbed by the metal | | *1: a black siliceous stone related to flint and formerly used to test the [[purity]] of gold and silver by the streak left on the stone when rubbed by the metal |
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| *3: a [[fundamental]] or quintessential part or feature : basis <a touchstone [[film]] of that decade> <now considered a touchstone of the [[city]]'s life — Michael Specter> | | *3: a [[fundamental]] or quintessential part or feature : basis <a touchstone [[film]] of that decade> <now considered a touchstone of the [[city]]'s life — Michael Specter> |
| ==Description== | | ==Description== |
− | A '''touchstone''' is a small tablet of dark stone such as [http://en.wikipedia.org/wiki/Fieldstone fieldstone], slate, or [http://en.wikipedia.org/wiki/Lydite lydite], used for [http://en.wikipedia.org/wiki/Metallurgical_assay assaying] precious metal alloys. It has a finely grained surface on which soft metals leave a visible trace. | + | A '''touchstone''' is a small tablet of dark stone such as [https://en.wikipedia.org/wiki/Fieldstone fieldstone], slate, or [https://en.wikipedia.org/wiki/Lydite lydite], used for [https://en.wikipedia.org/wiki/Metallurgical_assay assaying] precious metal alloys. It has a finely grained surface on which soft metals leave a visible trace. |
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− | The ''touchstone'' was used in [http://en.wikipedia.org/wiki/Ancient_Greece ancient Greece]. Its role in the introduction of monetary [[economy]] was explored by science historian [http://en.wikipedia.org/wiki/James_Burke_(science_historian) James Burke] in the second episode of his 1978 BBC television series ''[http://en.wikipedia.org/wiki/Connections_(TV_series) Connections]''. | + | The ''touchstone'' was used in [https://en.wikipedia.org/wiki/Ancient_Greece ancient Greece]. Its role in the introduction of monetary [[economy]] was explored by science historian [https://en.wikipedia.org/wiki/James_Burke_(science_historian) James Burke] in the second episode of his 1978 BBC television series ''[https://en.wikipedia.org/wiki/Connections_(TV_series) Connections]''. |
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| It was also used by Indus Valley Civilization about 3500 BC for testing the purity of soft metals. | | It was also used by Indus Valley Civilization about 3500 BC for testing the purity of soft metals. |
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− | Drawing a line with gold on a ''touchstone'' will leave a visible trace. Because different alloys of gold have different colours (see gold) the [[unknown]] sample can be compared to samples of known [[purity]]. This [[method]] has been used since ancient times. In [[modern]] times, additional tests can be done. The trace will react differently to specific [[concentrations]] of [http://en.wikipedia.org/wiki/Nitric_acid nitric acid] or [http://en.wikipedia.org/wiki/Aqua_regia aqua regia], thereby identifying the quality of the gold. Thus, 24 carat gold is not affected but 14 carat gold will show chemical activity. | + | Drawing a line with gold on a ''touchstone'' will leave a visible trace. Because different alloys of gold have different colours (see gold) the [[unknown]] sample can be compared to samples of known [[purity]]. This [[method]] has been used since ancient times. In [[modern]] times, additional tests can be done. The trace will react differently to specific [[concentrations]] of [https://en.wikipedia.org/wiki/Nitric_acid nitric acid] or [https://en.wikipedia.org/wiki/Aqua_regia aqua regia], thereby identifying the quality of the gold. Thus, 24 carat gold is not affected but 14 carat gold will show chemical activity. |
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− | As a [[metaphor]], a ''touchstone'' refers to any [[physical]] or [[intellectual]] measure by which the [[validity]] or merit of a concept can be tested. It is similar in use to an [http://en.wikipedia.org/wiki/Acid_test_(gold) acid test], [http://en.wikipedia.org/wiki/Litmus_test_(politics) litmus test] in politics, or, from a negative perspective, a [http://en.wikipedia.org/wiki/Shibboleth shibboleth] where the criterion is considered by some to be out-of-date. The word was introduced into literary criticism by [http://en.wikipedia.org/wiki/Matthew_Arnold Matthew Arnold] in "the Study of Poetry" (1880) to denote short but distinctive passages, selected from the [[writings]] of the greatest [[poets]], which he used to determine the relative [[value]] of passages or poems which are [[compared]] to them. Arnold proposed this method of [[evaluation]] as a corrective for what he called the "fallacious" estimates of poems according to their "historic" importance in the development of literature, or else according to their "personal" [[appeal]] to an individual critic. | + | As a [[metaphor]], a ''touchstone'' refers to any [[physical]] or [[intellectual]] measure by which the [[validity]] or merit of a concept can be tested. It is similar in use to an [https://en.wikipedia.org/wiki/Acid_test_(gold) acid test], [https://en.wikipedia.org/wiki/Litmus_test_(politics) litmus test] in politics, or, from a negative perspective, a [https://en.wikipedia.org/wiki/Shibboleth shibboleth] where the criterion is considered by some to be out-of-date. The word was introduced into literary criticism by [https://en.wikipedia.org/wiki/Matthew_Arnold Matthew Arnold] in "the Study of Poetry" (1880) to denote short but distinctive passages, selected from the [[writings]] of the greatest [[poets]], which he used to determine the relative [[value]] of passages or poems which are [[compared]] to them. Arnold proposed this method of [[evaluation]] as a corrective for what he called the "fallacious" estimates of poems according to their "historic" importance in the development of literature, or else according to their "personal" [[appeal]] to an individual critic. |
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| [[Category: The Sciences]] | | [[Category: The Sciences]] |
| [[Category: Languages and Literature]] | | [[Category: Languages and Literature]] |