Laboratory glassware and plastic wares are widely used in medical laboratories. Glasswares are usually manufactured from boro-silicate glass. Boro – silicate glass is a material with the following defined characteristics:
- Resistant to the action of chemical with the exception of hydrofluoric and phosphoric acid,
- Made to withstand mechanical breakage,
- Made to withstand sudden change of temperature.
Glassware produced from the soda lime type of glass does not fit the above requirements and is easily broken by mechanical stress produced by a sudden change of temperature. Hardened glasses, such as Pyrex, monax, and firmasil have low soda-line content and are manufactured especially to resist thermal shock (high temperature). The walls of these vessels are generally thicker than those made from soda lime. The high proportion of boro – silicate increases the chemical durability of the glasswares
- All glasswares must be handled carefully.
- Breakage can sometimes be dangerous and may result in the loss of valuable and irreplaceable materials.
- Flasks and beakers should be placed on a gauze mat when they are heated over a Bunsen flame. Gauze mat is made from asbestos and its function is to distribute the heat evenly.
- Test tubes exposed to a naked flame should be made of heat resistant glasses.
- If liquids are to be heated in a bath or boiling water, the glass contents should be heat resistant. N.B: Sudden cooling of hot glass should be avoided.
- When diluting concentrated acids, thin walled glassware should be used since the heat evolved by the procedure often cracks thick glasswares. Examples: – hydrochloric and sulfuric acid.
- Heat- expansion is liable to crack bottles if their caps are screwed on tightly so if heat is to be applied, flasks should