When heated with proper care Laboratory Glasswares will give long and satisfactory service. The following notes assist users in obtaining the maximum life and performance from their Laboratory Glassware.
HEATING & 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 heating of the vessel by slow movement of the vessel in relation to 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 this vessel.
Always use anti - bumping devices in 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 chance 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
To, Prevent scratching the inside of vessels always use a ' policemen' or similar device on stirring rods.
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 side of the vessel.
Never mix Sulphuric acid and water inside a glass - measuring cylinder. The heat of reaction can break the base of the cylinder.
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 pressure and never subject to sudden pressure changes.
JOINING AND SEPERATING GLASS APPRATUS
When storing glass stopcocks and joints insert a thin strip of paper between joint surfaces to prevent sticking.
Never store stopcocks for long periods with lubricant still on the ground surfaces.
Glass stopcocks on Burettes and Separating Funnels should be lubricated frequently to prevent sticking.
If a ground joint sticks, the use of penetrating oil will often prove useful in helping separation. Carefully rocking the cone in the socket or gently tapping the socket flange on a wooden surface can generally achieve separation.
In using lubricants it is advisable to apply a light coat of grease completely around the upper part of the joint and avoid greasing that part of the joint, which contacts the inner part of the apparatus.
(a) Hydrocarbon grease are commonly used on standard taper joints. Most laboratory solvents, including acetone, can easily remove it.
(b) For higher temperature or high vacuum applications, silicon grease is often preferred and it can be removed readily with chloroform.
(c) For long term reflux or extraction, glycerin grease is suitable and it is soluble in water.
Wear heavy protective gloves when inserting glass tubing into a bung. The use of water, oil or glycerol is recommended on both tubing and rubber bung while carrying this operation.
To prevent accidents use tong or asbestos gloves to remove all glassware from heat sources.
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.
When using concentrated acids, alkalies or potentially hazardous materials use mechanical means or pipetting. Avoid pipetting by mouth.
Label all containers before filling. Never fill unlabeled containers and throw away contents of unlabeled containers.
Do not look down into a test - tube to avoid any type of accident while test tube being heated or containing chemicals.
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 monoxinde, Hydrogen cynide 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 equipments, ensure the wire and plugs are in good condition. Never handle
electrical connection with damp hands.
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
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 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 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 forming 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 interface with 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°C.
Always protect clean glassware from dust by use of temporary closures or by placing in a dust free cabinet. For cleaning specific type of glassware, please refer the following pages.
CLEANING SPECIFIC TYPES OF GLASSWARE
Place pipettes tips down. in a cylinder or tall jar of water immediately after use. Gently place it on a pad of cotton or wool to prevent breaking of the tips. At a convenient time, the pipettes may then be drained and placed in a cylinder or jar of dissolved detergent or, if exceptionally dirty, in a jar of chromic acid cleaning solution. After soaking for several hours, or overnight, drain the pipettes and run tap water over and through them until all trace of dirt are removed. Soak the pipettes in distilled water, for at least one hour. Remove from the distilled water, dry the outside with a cloth shake out the water and dry.
In laboratories where a large number of pipettes are used daily, it is convenient to use an automatic pipette washer. Polyethylene baskets and jars may be used for soaking and rising pipettes in chromic acid cleaning solution.
After drying, place pipettes in a dust - free drawer, Wrap serological and bacteriological pipettes in paper or place in pipettes cans and sterilize in the dry air sterilizer at 160°C for two hours. Pipettes used for transferring infectious material should have a plug of cotton placed in the mouth end of the pipettes in chromic acid cleaning solution.
BUERETTES (WITH GLASS STOPCOCK)
Remove the stopcock key and wash the burette with detergent and water.
Rinse with the tap water until all the dirt is removed. Then rinse with distilled water and dry.
Wash the stopcock key separately. Before the stopcock key is replaced in the burette, lubricate the joint with a small amount of lubricant. REMEMBER THAT BURETTE STOPCOCK KEYS ARE NOT INTERCHANGEABLE,
Always cover burettes when not in use.
Culture tubes, which have been used, previously must be sterilized before cleaning. The best general method for sterilizing culture tubes is by autoclaving for 30 minutes at 121°C (15lb Pressure). Media that solidify on cooling should be poured out while the tubes are hot. After the tubes are emptied, brush with detergent and water, rinse thoroughly with tap water, rinse with distilled water, place in a basket and dry.
If tubes are to be filled with a medium, which is sterilized by autoclaving, do not plug until the medium is added. Both medium and tubes are thus sterilized with one autoclaving.
If the tubes are to be filled with a sterile medium or if they are to be sterilized by the fractional method and sterilized the tubes in the autoclave or dry air sterilizer before adding the medium.
Serological tubes should be chemically clean but need not be sterile. However, specimens of blood, which are to be kept for some time at room temperature, should be collected in a sterile container. It may be expedient to sterilize all tubes as routine.
To clean and sterilize tubes containing blood, discard the clots in a waste container and place the tubes in a large basket. Put the basket with others, in a large bucket or boiler. Cover with water, add a fair quantity of soft soap or detergent and boil for 30 minutes. Rinse the tubes and clean with brush, rinse and dry with the usual precautions.
It is imperative when washing serological glassware that all acid, alkali and detergent be completely removed. Both acid and alkali in small amounts destroy complement and in large amounts produce hemolysis. Detergents interfere with serological reactions.
Serological tubes and glassware should be kept separate from all other glassware and used for nothing except serological procedures.
DISHES AND CULTURE BOTTLES
Sterilize and clean as detailed under culture tubes.