The Collaborative International Dictionary
Touch-needle
Touch-needle \Touch"-nee`dle\, n. (Metal.) A small bar of gold and silver, either pure, or alloyed in some known proportion with copper, for trying the purity of articles of gold or silver by comparison of the streaks made by the article and the bar on a touchstone.
Wiktionary
touch-needle
n. A small bar of gold and silver, either pure, or alloyed in some known proportion with copper, for testing the purity of gold or silver articles by comparison of the streaks made by the article and the bar on a touchstone.