Safe Use Of Glassware
When heated with proper care Glassware will give long and satisfactory service. The following notes assist users in obtaining the maximum life and performance from their Glassware.
Heating And Cooling
Glass may suffer damage in three ways :
- It may break under thermal stress in the `steady state`.
- It may break under sudden heating or cooling.
- Glass if heated beyond certain temperature, may acquire a permanent stress on cooling which could cause subsequent failure.
The following suggestions will help in avoiding failures during heating and cooling procedures.
- During evaporation, never leave vessel unattended. Lower the temperature gradually as the liquid level drops, to avoid dryness condition, otherwise glass vessel may crack or explode.
- Always use caution when placing heated vessel on a cold or damp surface. Sudden temperature may cause the vessel to break.
- Always cool vessels slowly to avoid thermal breakage.
- Never apply heat to badly scratched or etched vessel to prevent chance of breakage.
- Avoid point source of heating to a vessel and always diffuse it by using a metal gauge or air/water bath. Alternatively ensure uniform heating of the vessel by slow movement of the vessel in relation the heat source.
- Uniform heat is critical factor for some chemical reactions. For this adjust large soft flame of Bunsen burner to heat slowly but also more uniformly.
- Adjust the flame contacts and heat the vessel below the liquid level to avoid breakage of the vessel.
- Always use anti-bumping devices in the vessel, such as pumice or glass wool when rapid heating of the vessel and contents is required and to prevent internal abrasions of the vessels.
- Thick walled glassware are best heated with the use of an electric immersion heater and should not subjected to direct flame or other localized heat source.
- Do not heat glassware`s over electric heaters with open elements to avoid localized stress and chances of breakage.
- Always ensure that the surface of the hot plate is larger in area than the base of the vessel being heated to prevent uneven heating and glassware breakage.
- When using electrical appliances always ensure to follow manufacturer`s instructions.
Mixing And Stirring
- When using a glass vessel with a magnetic stirrer always uses a covered follower to prevent abrading the inside of the vessel.
- Before using glass or metal mechanical stirrer in a glass vessel, predetermine the height of the stirrer to ensure there is no contact between the stirrer blades and the bottom or sides of the vessel.
Vacuum And Pressure
- Always follow safety measures when working with glassware subjected to pressure or vacuum.
- Never use glassware beyond the recommended safe limit.
- Gradually apply and release positive and negative pressures and never subject to sudden pressure changes.
Personal Safety
- To prevent accidents use tongs or asbestos gloves to remove all glassware from heat source.
- Follow safety measures.
- Before opening Acid bottle, always flush the outside of bottle with water.
- All mercury containers should be kept well stoppered. Mercury toxicity is cumulative and element`s ability to amalgamate with a number of metals is well known.
- Never taste or smell chemicals for identification and never drink from a beaker.
- Label all containers before filling. Never fill unlabeled containers and throw away contents of unlabeled containers.
- Do not permit glass-to-metal contact when clamping glassware, and do not excessively tighten the clamps to avoid breakages.
- Splattering from acids, caustic materials and strong oxidizing solutions on the skin or clothing should be washed off immediately with large quantities of water.
- When working with chlorine, hydrogen, sulphide, carbon monoxide, hydrogen cyanide and other very toxic substances, always use a protective mask or perform these experiments under a fume hood in a well-ventilated area.
- In working with volatile materials, remember that heat causes expansion and confinement of expansion results in explosion.
- Perchloric acid is especially dangerous because it explodes on contact with organic materials. Do not use perchloric acid around wooden benches or tables. Keep perchloric acid bottles on glass or ceramic trays having enough volume to hold all the acid in case the bottle breaks. When using perchloric acid, always wear protective clothing.
- When using hot plates and other electrical equipment, ensure the wire and plugs are in good condition. Never handle electrical connection with damp hands.
Cleaning
Successful experimental results can only be achieved by using a clean apparatus. In all instances laboratory glassware must be physically clean, in nearly all cases it must be chemically clean and in specific cases it must be bacteriological clean or sterile. There must be no trace of grease and safest criteria of cleanliness are the uniform wetting of the glass surface by distilled water. Any prevention of uniform wetting of the surface will introduce errors such as distortion of the meniscus and accuracy of volume.
General Cleaning
- Experienced personnel must solely undertake. cleaning of glassware, which contain hazardous materials.
- Most new glassware is slightly alkaline in reaction. For precision chemical tests, new glassware should be soaked several hours in acid water (1% solution hydrochloric acid or nitric acid) before washing.
- Glassware, which is contaminated with blood clots, culture media, etc., must be sterilized before cleaning.
- If glassware becomes unduly clouded or dirty or contains coagulated organic matter, it must be cleaned with chromic acid cleaning solution. The dichromate`s should be handled with extreme care because it is a powerful corrosive.
- Wash glassware, as quickly as possible after use but if delays are unavoidable, the articles should be allowed to soak in water.
- Grease is removed by weak sodium carbonate solution or acetone or fat solvents. Never use strong alkalis.
- Hot water with recommended detergents should be used and if glass is exceptionally dirty a cleaning powder with a mild abrasive action can be applied – provided the surface is not scratched.
- During the washing all parts of the article should be thoroughly scrubbed with a brush selected for the shape and size of the glassware. Brushes should always be in good condition to avoid any abrasion of the glassware.
- When chromic acid solution is used, the item may be rinsed with the cleaning solution or it may be filled and allowed to stand-the amount of time depending on amount of contamination on the glassware.
- Special types of precipitate material may require removal with nitric acid, aqua regia or fuming sulphuric acid. These are very corrosive substances and should be used only when required.
- It is imperative that all soap detergents and other cleaning fluids be removed from glassware before use. This is especially important with the detergents, slightly traces of which will interfere with serological and culture reactions. After cleaning, thoroughly rinse with tap water ensuring that containers are partly filled water, shaken and emptied several times. Finally rinse with demonized or distilled water.
- Drying can be undertaken either in baskets or on pegs in air or at a temperature not exceeding 120 OC.
- Always protect clean glassware from dust by use of temporary closures or by placing in a dust free cabinet.
