Watch glass 表面皿
(重定向自Watchglass)
A watch glass is a circular concave piece of glass used in chemistry as a surface to evaporate a liquid, to hold solids while being weighed, as a cover for a beaker, and for heating a small amount of substance. The latter use is generally applied to prevent dust or other particles entering the beaker; the watch glass does not completely seal the beaker, so gas exchanges still occur.