Watch Glass Definition and Meaning
Although one may think that a watch glass is very simple in its structure, this laboratory glassware is very useful in several ways, which scientists would require. In a more formal description, this is a circular, more often than not concave shape structure that is usually made from glass and other transparent materials. Literally from its name one infers that the watch glass is used mainly in sample preparation evaporation, weighing, and as a cover. This article discusses in detail what a watch with glass is, how it is used, what benefits it brings, the types available, and the safety aspects of the use of such glass.
What is a Watch Glass?
A watch glass is a type of container (glass) that is round and shaped like a dome albeit less pronounced and it further resembles a pocket watch lid which accounts for the origin of the watch glass. They are usually made from soda-lime glass or borosilicate glass. Because of its rounded shape, it can be used to store small amounts of liquid or solids without any risk of spillage. It is commonly used to increase the rate of evaporation of a liquid, as a lid for beakers, to balance items as well, and to support small reaction vessels.
Watch glasses tend to have a few standard sizes which will generally fall in the range of 50mm to 150mm for use in different laboratories. They are usually clear in color observing the sample effortlessly without hindrance. Though normally found in chemistry laboratories, glasses are used in biological, environmental, and even educational labs.
Key Features of a Watch Glass
Material Composition
- Watch glasses are usually made up of borosilicate glass. This type of glass cannot be easily broken by heat or chemically damaged.
- Ancillary, some glasses are manufactured with quartz to help in environments with more elevated temperatures for special experiments.
- It is easy to see the contents without the picked lid up due to the clarity which the close cover has.
Concave Shape
- This little inclination serves two purposes retaining liquids without pouring out and aiding in evaporation by increasing the area of the surface.
- In addition, it retains particles or contaminants from going out or coming in when it is employed to cover.
Variety of Sizes
- Various sizes of watch glasses are available such as beaker covers, or for carrying out simple experiments extending their use to other laboratory functions.
Uses of Watch Glass Chemistry Laboratories
Irrespective of the simplicity, the watch glass is one of such items in the laboratory that has a variety of functions. Here are some of the more popular ones:
Evaporating of Solvent: Typically, the watch glass is used for evaporating solvents or small amounts of liquid. The convex shape makes it more difficult to hold a small liquid about the amount of liquid in the concave glass which will make evaporation easy. This is more important in the qualitative aspect of chemical analysis where there is a need to concentrate or even dry some substances.
Determination of Small Amounts: Because of its lightweight and flat shape, a watch glass is usually utilized for weighing small solids or powders. It can be placed on an analytical balance to hold the sample during weighing for measurement to avoid inaccuracies and contamination.
Lid for Beakers and Flasks: Watch glasses are also used as lids while carrying out a reaction in a beaker or machine flask, That helps prevent contaminating the mixture but allows for gas exchange, which is not available with a tight lid. Also, when carrying out an acid-base titration or boiling solution in a flask, a watch glass concave slides over the mouth to prevent spilling without closing the flask.
Small Reactions Frequently Occurring: When performing tiny reactions or microscale reactions, Watch glass is used as a reaction medium. They are transparent and therefore it is easy to observe the color change, formation of a precipitate, and other changes that occur during the reaction.
Holding Samples: Now, watch glasses are also employed as small holding and drying vessels for small solid samples that may have been filtered or spun down by using a centrifuge. As they are often utilized in gravimetric analysis for holding the precipitate which will be subsequently weighed.
Crystallization: In some situations, glasses act as lids to prevent spillage while a solution is evaporated slowly to promote crystallization.
Types of Watch Glasses
There are different types of glasses available, each with certain functions in the laboratory:
Standard Borosilicate Watch Glass.
This is the most commonly used type for various activities such as evaporation, weighing and even covering a beaker in general laboratory use. Borosilicate glass comes as a very strong and shock-resistant material that withstands both heat and cold in use.
High-Temperature Quartz Watch Glass
Quartz glasses are suitable for high temperatures with an application to a reaction or an experiment that requires temperatures of more than glass for instance borosilicate glass.
Frosted Watch Glass.
Frosted glasses have a matte finish on one side and this can be helpful in areas where standard clear glass and glare or reflection is a limitation.
Colored Glasses
While this type is not very popular, some watch glasses are produced in colors for certain experiments that are light sensitive and where the standard boring light would spoil the results.
Advantages of Using Watch Glasses in any Laboratory Setting
Heat Resistance: Also known as low-expansion glass, Borosilicate glass tolerates heat well and is useful for conducting heat-activated experiments without breaking down. The material maintains stability and resistance in thermal expansion allowing lower chances of shattering.
Chemical Resistance: It can withstand the most reactive species, a property that ensures that the periodical glasses do not react with the substances that they are being used to test or hold.
Ease of Use: This is lightweight, quick in preparation, easy to clean, and simple to handle, and thus such implements are essential both for elementary and complex activities within the laboratory.
Economical: With minimal cost and great strength, watch glasses are therefore reasonable and adequate for a variety of laboratory needs.
Non-reactive Surface: Glass is inert so it will not corrupt the material and interfere with the materials being worked on.
Factors to Remember Regarding the Use
Watch glasses are quite safe for day-to-day activities, but a few recommendations should be followed.
Use Gently: Most glasses made of glass would break when dropped or mistreated hence use safe precautions at all times. Always ensure that the watch glass is handled with utmost care to prevent such accidents from happening.
Avoid Rapid Temperature Changes: Though made from heat-tolerant borosilicate glass, exposing it to extreme thermal changes can easily break or shatter the glass. After taking away the heat from the glassware start heating it slowly.
Appropriate Tools That Need to Be Used: During the manipulation of circular watch glass be sure to utilize tongs or heatproof gloves to prevent any chances of sustained burns.
Do Not Overheat: Yes, watch glasses can withstand heat, but this is only to a certain point. Heat them too much, and they may also get damaged due to thermal stress.
Storage: Protect the watch glasses from cracking or breakage by keeping them in a safe place where no impact or pressure will be applied.
Conclusion
The watch glass is one of the most important equipment in any laboratory regardless of its relatively simple build. Whether it is used for evaporation, for weighing purposes, as a cover for beakers, or carrying out microscale reactions, their versatility makes this piece of glassware a necessity. The glass made of synthetic materials like borosilicate or quartz is mesoporous and chemically resistant, thus making it effective in a wide range of research and experimental applications due to its high-temperature tolerance. Knowing how it is utilized, different varieties and how safe it is will promote performing these activities well in the laboratory.
