Glass types
The following are the types of glass that are commonly used to make laboratory glassware.
1. High Thermal Resistant Glass type
2. High Silica Glass
It contains 96% silica and is made from borosilicate glass by removing all elements except for silica. This heat-stable glass is used for high precision analytical work. It is also used in the manufacturing of reflectors and mirrors.
3. High Alkali Resistant Glass
It is boron free glass with much less thermal resistance and is often called µsoft glass and must be heated and cooled very carefully. Its use should be limited to procedures where strong alkalis are to be used.
4. Low Actinic Glass
It contains materials which usually impart an amber or red color to the glass and reduce the amount of light transmitted to the substance in the glassware. It is used for keeping substances that are particularly sensitive to light, such as silver nitrate.
5. Standard Flint Glass or Soda Lime Glass
It is composed of the mixture of oxides of silicon, calcium, and sodium. It is the most inexpensive glass but is less resistant to high temperatures and chemicals.THE CLEANING OF GLASSWARE
All glassware for the laboratory must be washed and cleaned thoroughly. In most cases, it must be cleaned chemically and, in some cases, it must be cleaned from micro-organisms i.e. it needs to be sterile. Glassware that cannot be cleaned immediately after use should be rinsed with tap water and left to soak in a basin to which a small amount of detergent is added. Never allow dirty glassware to dry out. New glassware is often slightly alkaline and should be soaked for several hours in a dilute hydrochloric or nitric acid solution and then washed in the usual manner.
General Cleaning Procedures
Most glassware (with the exception of pipettes) can be cleaned in the following way:
1. Put the specified amount of detergent into a dishpan containing moderately warm water.
2. Rinse the glassware in tap water & then put it in detergent solution for at least one hour.
3. Using a cleaning brush, thoroughly scrub the glassware. Avoid using abrasive cleaners.
4. Rinse glassware under running tap water. Allow water to run into each piece of glassware, pour it out & repeat several times (7-10). Rinse the outside of glassware also.
5. Rinse inside and out with distilled water.
6. Glassware may be dried in a hot-air oven at 50-100°C or at room temperature. Always dry glassware or other equipment in an inverted position to ensure complete drainage of the water as it dries.
7. Check the glassware for cleanliness by observing the water drainage--chemically cleaned glassware will drain uniformly. Dirty glassware will leave water droplets adhering to the wall of the glassware.
Cleaning Pipettes:
1. Immediately after use, place the pipettes in a special pipette container that has enough water in it to completely cover the pipettes.
2. Place them in a cleaning solution (a mixture of sulphuric acid and potassium dichromate). (A detergent solution may also be used). Soak for 30 minutes.
3. Rinse thoroughly in tap water to remove traces of the cleaning solution.
4. Rinse 2-3 times in de-ionized water.
5. Dry in a hot-air oven.
Cleaning Diluting Pipettes:
1. Rinse immediately after use.
2. First clean with tap water, then with distilled water. Finally, rinse with either alcohol or acetone.
Cleaning Photometry Cuvettes:
2. Immediately after use, rinse with tap water and fill with a mild detergent solution and place in a special test-tube rack.
3. Rinse with tap water and, finally, with distilled water.
4. Dry in a medium-hot oven (less than 100°C).
