3.3 LOW EXPANSION BOROSILICATE GLASS

From the 16th Century to, today, chemical research teams have used glass containers for a very basic reason the glass containers is transparent, almost invisible. And so the contents and the reaction are clearly visible, But because chemists must heat, cool and mix chemical substances, ordinary glass is not always adequate for laboratory works.

Laboratory works requires apparatus made in a glass - which can readily be moulded into any desired shape or from, which offers maximum inertness when in contact with the widest range of chemical substances, which can withstand thermal shock with fracture and high temperature work without deforming, and which will be resillient enough to survive the everyday knocks to which it will be subjected in normal laboratory handling, washing and sterilizing processes.

Chemical Composition

LOBAlife - Glassco Glassware is a low alkali borosilicate composition. Its typical chemical composition is given under. It is virtually free of magnesia-lime-Zinc group and contains only traces of heavy metals.

Thermal Properties

As the Coefficient of thermal expansion of Borosilicate glass is low, the thermal stresses under a given temperature gradient are consequently low and the glass can withstand higher temperature gradients and also sudden temperature changes/thermal shocks. Minute scratching of glass surface can however reduce its thermal resistance.

In general the ‘Strain Point’ should be regarded as the maximum safe operating temperature of LOBAlife - Glassco glassware. When heated above 500°C the glass may acquire permanent stresses on cooling. All LOBAlife - Glassco labware is annealed in modern ovens under strictly controlled conditions to ensure minimal residual stress in the products.

Chemical Durability

LOBAlife - Glassco Glassware in highly resistance to water, neutral and acid solutions, concentrated acids and their mixtures as well as to chloride, bromine, iodine, and organic matters. Even during extended period of reaction and at temperatures above 100°C, its chemical resistance exceeds that of most metals and other materials.

It can withstand repeated dry and wet sterilisation without surface deterioration and subsequent contamination. Resistance to attack of various chemicals is shown under. Only hydroflioric acid, very hot phosphoric acid and alkaline solutions increasinglly attack the glass surface with rising concentration and temperature.

Fabrication with 3.3 Borosilicate Glass

Due to low expansion of glass and easy workability, this glass can be shaped, formed, joined into complicated apparatus. It can be done even by an analyst in his own laboratory. He can keep on changing till he gets what he needs. In case where annealing in a controlled oven is difficult he can do so by flame annealing which is also great advantage.

Optical Properties

Laboratory glassware made from 3.3 Borosilicate Glass shows no noticeable absorption in the visible region of the spectrum. It appear consquently clear and colourless. When treated with proper care LOBAlife - Glassco laboratory apparatus will give a long and satisfactory service. The following prepared notes are to assist users in obtaining the maximum life and performance from their apparatus. Our sales department will be happy to advise on any aspect concerning the safe use of our products.

HEATING AND COOLING

• Glass may suffer damage in three ways :

• It may break under thermal stress in the steady state, that is when there is established constant thermal gradient through the glass.

• It may break under the transient stress of a ‘thermal shock’, that is sudden heating or cooling

• It may, if heated beyond certain temperature, acquire a permanent stress on cooling which could cause subsequent failure.

The following precautionary measures will assist in avoiding failures during heating and cooling procedures.

1. Never leave vessel unattended when evaporation work is being carried out. The vessel may crack or explode as dryness condition is approached if the heat source is not adjusted correctly. Lower the temperature gradually as the liquid level drops.

2. Always use caution when removing glassware from a heat source and avoid placing on a cold or damp surface. Although the ware can withstand extreme temperatures, sudden temperature changes may cause the vessel to break.

3. Always cool vessels slowly to prevent thermal breakage.

4. Never apply heat to badly scratched or etched vessel as the thermal strength will have been greatly reduced.

5. Never apply point source heating to a vessel as this will greatly increase the chance of breakage.

6. Always diffuse the heat source by using a metal gauze or air/water bath. Alternatively ensure even heating of the vessel byslow movement of the vessel in relation to the heat source.

7. Adjust Bunsen burner to get a large soft flame. It will heat slowly but also more uniformly. Uniform heat is critical factor for some chemical reactions.

8. Ensure that the flame contacts the vessel below the liquid level. Heating above that level will invite breakage of the vessels.

9. Always use anti-bumping devices in the vessel, such as powered pumice or glass wool rapid heating of the vessel and contents is required.

10. Never use material with sharp edges such as broken porcelain as an anti-bumping device. This will cause internal abrasions and reduce the mechanical and thermal strength of the vessel.

11. Thick walled glassware should not be subjected to direct flame or other localised heat source. Vessels of this type are best heated with the use of an electric immersion heater.

12. Avoid heating glassware over electric heaters with open elements. Uneven heat of this type can include localised stress and increase the chance of breakage.

13. Remember that the hot plate will retain heat long after the appliance has been switched off.

14. Always ensure that the surface of the hot plate is larger in area than the base of the vessel being heated. An under-sized plate of the job in hand will invite uneven heating and promote breakage of glassware.

15. Always ensure that manufacturer’s instructions are Bollowed when electrical heat sources.

Mixing and Stirring

1. Always use a policemen’s or similar device on stirring rods to prevent scratching the inside of a vessel.

2. When using a glass vessel with a magnetic stirrer always use a covered follower to prevent abrading the inside of the vessel.

3. When using glass or metal mechanical stirrer in a glass vessel always predetermine the height of the stirrer before use to ensure there is no contact between the stirrer blade and the bottom or sides of the vessel.

4. 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

1. Never use a glassware beyond the recommended safe limit.

2. Always use a safety screen when working with glassware subjected to pressure of vacuum,

3. Never subject glassware to sudden pressure changes. Always apply and release positive and negative pressures gradually.

Joining and Separating glass apparatus

1. When storing glass stopcocks and joints, insert a thin strip of paper between joint surfaces to prevent sticking.

2. Never store stopcocks for long periods with lubricant still on the ground surfaces.

3. Glass stopcocks on Burettes and Separation Funnels should be lubricated frequently to prevent sticking.

4. If a ground joint sticks, separation can generally be achieved by carefully recking the cone in the socket, or gently tapping of the socket flange on a wooden surface, or by heating the socket and not the cone in a localised flame. The use of penetrating oil will often prove useful in aiding separation.

5. In using lubricants it is advisable to apply light coat of grease completely around the upper part of the joint. Use only a small amount and avoid greasing that part of the joint which contacts the inner part of apparatus.

6. Three type of lubricants are commonly use on standard taper joints A) Hydrocarbon grease is the most widely used. It can be easily remove by most laboratory solvents, including acetone. (B) Because hydrocarbon grease is so easily removable, silicon grease is often preferred for higher temperature or high vacuum applications. It can be removed readily with chloroform. (C) For long term reflux or extraction reactions, a water soluble, organic and insoluble grease, such as glycerin, is suitable. Water will clean glycerin.
   There are other type of greases which can be used specifically when certain reagents are used in the Burettes or Separating Funnels.

7. The use of water, oil or glycerol is recommended on both tubing and rubber bung when inserting glass tubing into a bung. Always wear heavy protective gloves or similar protection when carrying out this operation.

8. Always fire polish rough ends of glass tubing before attempting to insert into flexible tubing. The lubricants recommended above may also prove useful.

9. Never attempt to pull a thermometer out of a rubber bung. Always cut the bung away.

PERSONAL SAFETY

1. Use tongs to asbestos gloves to remove all glassware from heat. Hot glass can cause severs burns.

2. Protective gloves, safety shoes, aprons, and goggles should be worn as safety chemical accidents, spilling or splattering.

3. Always flush the outside of acid bottle with water before opening. Do not put the stopper on the counter top where someone else may come in contact with acid residue.

4. Special care is needed when dealing with mercury. Even a small amount of mercury in the bottom of a drawer can poison the room atmosphere. Mercury toxicity is cumulative and the element’s ability to amalgamate with a number of metals is well known. After an accident involving mercury, the area should be cleaned carefully until there are no globules remaining.
   All mercury containers should be kept well-stoppered.

5. Never drink from a beaker. A beaker left specifically for drinking is a menace to the laboratory. Do not taste chemicals for identification. Smell chemicals only when necessary and by waiting a small amount of vapour towards the nose.

6. Avoid pipeting by mouth, particularly when using concentrated acids, alkalis or potentially biohazardous materials. Use mechanical means such as a rubber bulb or an automatic dispenser.

7. Never fill receptacle with material other than that called for by the label. Label all containers before filling. Throw away contents of unlabelled containers.

8. To avoid breakage when clamping glassware, do not permit glass-to-metal contact and do not use excessive force to tighten the clamps.

9. Do not look down into a test tube being heated or containing chemicals and do not point its open end at another person. A reaction might cause the contents to be ejected, resulting in injury.

10. Spattering from acids, caustic materials and strong oxidizing solutions on the skin or clothing should be washed off immediately with large quantities of water.

11. 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 on a well ventilated area.

12. In working with volatile materials, remember that heat causes expansion and confinement of expansion results in explosion. Remember also that danger exists even though external heat is not applied.

13. 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, wear protective clothing.

14. When using hot plates and other electrical equipments, 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 bacteriologically clean or sterile. There must be no trace of grease and the safest criteria of cleanliness is the uniform wetting of the glass surface by distilled water-this being of the utmost importance for glassware used for volumetric methods. Any prevention of uniform wetting of the surface will introduce errors such as distortion of the meniscus and accuracy of volume.
 

GENERAL CLEANING

1. Cleaning of glassware which has contained hazardous materials must be solely undertaken by experienced personal.

2. 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.

3. Glassware which is contaminated with blood clots, culture media, etc. must be sterilized before cleaning.

4. If glassware become induly clouded or dirty or contains coagulated organic matter, it must be cleaned with chromic acid cleaning solution. The dichromates should be handle with extreme care because it is a powerful corrosive.

5. Wash glassware as quickly as possible after use but if delays are unavoidable, the articles should be allowed to soak in water.

6. Grease is removed by weak sodium carbonate solution or acetone or fat solvents. Never use strong alkalis.

7. Hot water with recommended detergents should be used and if glass is exceptionally dirty a cleaning power with a mild abrasive action can be applied, provided the surface is not scratched.

8. During washing all parts of the article should be throughly 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 glassware.

9. 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 should depend on amount of contamination on the glassware.

10. Special type of precipitate material may required removal with nitric acid, aqua regia or fuming sulphuric acid. These are very corrosive substances and should be used only when required.

11. It is imperative that all soap detergents and other cleaning fluids be removed from glassware before use. This is especially important with the detergents, slight traces of which will interfere with serologic and culture reactions. After cleaning, thoroughly rinse with tap water ensuring that containers are partly filled with water. shaken and emptied several times. Finally rinse with deionised or distilled water.

12. Drying can be undertaken either in baskets or on pages in air or at a temperature not exceeding 120°C.

13. 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 Pipettes

1. Place pipettes tips down, in a cylinder or tall jar of water immediately after use. Do not drop them into the jar, since this may break or chip the tips and render the pipettes useless for accurate measurements. A pad of cotton or glass wool at the bottom of the jar will help to prevent breaking of the tips. Be certain that the water level is high enough to immerse the greater portion or all or each pipette. At a convenient time, the pipettes may then be drained and placed and 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 then until all traces 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.

Burettes (with glass stopcock)

1. Remove the stopcock key and wash the burette with detergent and water.

2. Rinse with tap water until all the dirt is removed. Then rinse with distilled water and dry.

3. Wash the stopcock key separately. Before the stopcock key is replaced in the buretts stopcock key are not interchangeable

4.  Always cover burettes when not in use.

Culture Tubes

1. Culture tubes which have been used previously must be sterilized before cleaning. The best general method for sterilising culture tubes is by autoclaving for 30 minutes at 121°C (15ib. pressure). Media which solidify on cooling should be poured out while the tubes are emptied, brush with detergent and water, rinse throughly with tap water, rinse with distilled water, place in a basket and dry.

2. If tubes are to be filled with a medium which is sterilized by autoclaving, do not plug until the medium is added .Both medium & tubes are thus sterilized with one autoclave.

3. If the tubes are to be filled with a sterile medium or if they are to be sterilized by the fractional method then sterilize the tubes in the autoclave or dry air sterilizer before adding the medium.

Serological Tube

1. 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 expendient to sterilize all tubes as routine.

2. 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 soap or detergent and boil for 30 minutes. Rinse the tubes and clean with brush, rinse and dry with the usual precautions.

3. 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 serologic reactions.

4. Serological tubes and glassware should be kept separate from all other glassware and used for nothing except serologic procedures.