STRASS. - Remarkably faithful imitations of every kind of precious stone can be made from suitably prepared and, when necessary, coloured glass. The transparent basis front which artificial precious stones is prepared is called stress or paste, a material which must of necessity be the purest, most transparent, and most highly refractive glass that can be prepared. These qualities are combined in the highest degree in a flint glass of unusual density from the very large percentage of lead it contains. Among various mixtures given by Donault-Wieland as suitable for stress the following is an example : - powdered quartz 300 parts, red lead 470, potash (purified by alcohol) 163, borax 22, and white arsenic 1 part by weight. Special precautions are adopted in the melting of the materials, and the finished colourless glass is used for imitating diamonds. When employed to imitate coloured precious stones the strass is melted tilt with various metallic oxides, to which reference will be made under coloured glass. Artificial precious stones are, of course, easily distinguished from real stones by their infei jar hardnes4, and by chemical tests. They may also be generally detected by a comparatively soft warm sensation they communicate when applied to the tongue.