laboratory glassware; a shallow glass dish used as an
evaporating surface or to cover a beaker shallow glass dish used
to evaporate liquids, like the glass piece covering a pocket
watch A watch glass is a circular, slightly piece of glass used
in chemistry as a surface to evaporate a liquid, or as a cover
for a beaker. The latter use is generally applied to prevent
dust or other particles entering the beaker; the watch glass
does not completely seal the beaker, and so gas exchanges still
occur. a protective cover that protects the face of a watch