Touch-needles
Used by assayers and refiners; are little bars of gold, silver, and copper combined together in all the different proportions and degrees of mixture. Their use is to discover the degree of purity of any piece of gold or silver by comparing the marks they leave on the touchstone with those of the bars. The touchstone is usually a piece of hard black basalt. See ASSAYING; BASALT.
Toughened Glass is made by plunging the glass into a bath containing an oleaginous mixture after heating almost to melting-point the articles to be toughened, the bath itself being at a high temperature, but not so high as the glass itself. Some of the articles are thus toughened without any previous annealing--simply dropping them from the workman's rod directly into the bath.