Watch glass
From Wikipedia, the free encyclopedia
A watch glass is a circular, slightly concave 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.
When used as an evaporation surface, a watch glass allows closer observation of precipitates or crystallisation, and can be placed on a surface of contrasting colour to improve the visibility overall.
Watch glasses are so named because they are identical to the glass used for the front of old-fashioned pocket watches. In reference to this, large watch glasses are occasionally known as clock glasses.
Agar plate • Aspirator • Autoclave • Bunsen burner • Calorimeter • Colony counter • Colorimeter • Centrifuge • Fume hood • Incubator • Laminar flow cabinet • Magnetic stirrer • Microscope • Microtiter plate • Plate reader • Spectrophotometer • Stir bar • Thermometer • Vortex mixer • Static mixer
Laboratory glassware
Beaker • Boiling tube • Büchner funnel • Burette • Condenser • Conical measure • Crucible • Cuvette • Laboratory flasks (Erlenmeyer flask, Round-bottom flask, Florence flask, Volumetric flask, Büchner flask, Retort) • Gas syringe • Graduated cylinder • Pipette • Petri dish • Separating funnel • Soxhlet extractor • Test tube • Thistle tube • Watch glass
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