While chemists and researchers are making increased use of plastic in the laboratory, glass is still the choice of many. Obviously, deciding whether glass or plastic is right for the job at hand depends on various elements such as instrument design, material characteristics, and cost. But glass is the choice of many for many good reasons.
Glass out-performs plastic with its high chemical resistance against many substances, including acids, alkalis, organic solvents, saline solutions, and water. The only substances that can destroy glass are hydrofluoric acid, strong alkalis used at high temperatures, and concentrated phosphoric acid.
Additional advantages to using glass in the lab include its dimensional stability, even at high temperatures, and its transparency. Other advantages include the fact that many sizes of many pieces of laboratory equipment are available, and glass is easy to clean. It is suitable for reagent and chemical storage, and Pyrex, a type of glass, is resilient to heat.
There are different kinds of technical glass types available, each with different properties, making them useful for differing applications. These are:
Soda-lime glass: eg. AR-Glas is suitable for short exposure to chemicals, and for limited heat stress because of its good physical and chemical properties. Products manufactured from this kind of glass include culture tubes and pipettes.
Borosilicate glass: eg. BORO 3.3, BORO 5.0 Once again, this type of glass has good physical and chemical properties. BORO 3.3 has the ability to withstand a high variety of chemicals and temperatures and has good thermal shock and mechanical stability capabilities.
Laboratory glassware is a large variety of equipment used in science that has, up until the advent of some plastic alternatives, been traditionally made from glass. Glass is used in analytical laboratories, as well as in chemistry and biology.
Glass can be formed into many shapes and sizes by molding, cutting, bending, and blowing. Because of the possibility of breakage, many laboratories train first-time staff in how to use glassware in the lab correctly, and about the potential hazards inherent in working with glass.
When you work with glass in the laboratory, it is important to remember its limitations in regard to mechanical stress and thermal shock. Ensure that you take strict safety measures at all times. When inducing an exothermic reaction, such as when you dilute sulphuric acid, make sure you stir and cool, and that the reaction takes place in a suitable vessel.
This could be an Erlenmeyer flask. Avoid using graduated cylinders and volumetric flasks for exothermic reactions. Do not heat volumetric instruments on heating plates or you run the risk of breakage.
Do not expose glass instruments to sudden temperature changes or to sudden pressure changes. For example, do not let air quickly into evacuated glass apparatus, and never evacuate vessels with flat bottoms. They are not designed for vacuum use. Only apply effort (not force) steadily and in a controlled manner on empty glass instruments. Use safety devices such as goggles, gloves, and screens.
In terms of thermal resistance, glass should be heated to a temperature somewhere between the lower and upper annealing point. It should be kept at that temperature for about 30 minutes. It should then be cooled according to prescribed cooling rates.
The tensile strength of glass is fairly low, a factor that is greatly enhanced by the presence of cracks or scratches. In terms of resistance to temperature changes, the glass should be properly heated and cooled so that permissible mechanical loads are not exceeded, and breakage is avoided. Different types of glass show different levels of temperature change resistance.
Glass reacts minimally with water and acids at the surface level. Only tiny amounts are dissolved from the glass, through which a layer of silica gel forms on the surface to stop a further attack.
Hydrofluoric acid and hot phosphoric acid do, however, prevent such a layer from forming. Alkalis do attack the glass surface at high concentrations and temperatures, sometimes resulting in the destruction of graduations of volumetric instruments, or a change in volume.
First of all, clean the apparatus in cold water to ensure that any protein residues are removed. Then, soak the glassware in a disinfectant solution that is mixed at the correct dilution ratio.
Use a bristle brush to remove any material adhering to the surface of the glass. Then soak again, or use an ultrasonic bath. Rinse the item in deionized water three times to remove any detergent that might be lurking. Drain on a rack, and then dry in a clean environment or a hot air oven.