Watch glasses are made of glass material, round, slightly concave in the middle, similar to evaporating dishes. It can be used to evaporate liquids. It can increase the surface area of liquids, thus speeding up evaporation. But it can't be heated like an evaporating dish. It needs to be covered with asbestos nets. It can be used as a cover to cover the evaporating dish or beaker to prevent dust from falling into the evaporating dish or beaker. It can be used as a container to temporarily store solid or liquid reagents for easy access. It can also be used as a carrier to carry PH test paper so that a-cid or alkali drops on the test paper do not corrode the test bench.

Wash and dry the watch glass before use. Watch glasses are widely used.However, no matter what utensil is replaced, it should be used in accordance with the use of various utensils. For gas chamber identification, two pieces of watch glass are attached to one of the above glass surface by a test paper soaked with reagents in a grinding flat synthetic gas chamber. The identified compounds are placed on the following glass surface. When necessary, they are warmed up to observe the formation of gas-es in the reaction, and the gas-es are identified by changing the color of the reagents. If a piece of black paper is placed on the bottom wall of the watch glass when observing white precipitation or turbidity, the white products can be clearly visible. If you make all kinds of instrument caps, just use its arc to put on the utensil mouth and keep it stable, but you should pay attention to the choice of watch glass according to the caliber of the utensil. Generally, the diameter of the watch glass should be larger than the caliber of the utensil 1 cm, so it is more convenient to use. If it is used as beaker cover, watch glass of different diameters should be selected according to beaker capacity.