School Science Lessons
2024-06-23
Physics equipment, charcoal, glass cutting, microscopes, soldering
(UNPh06)
Contents
2.1.0 Charcoal, Activated charcoal
2.2.0 Equipment care
2.3.0 Glass cutting, tubing, cleaning
2.4.0 Laboratory items
2.5.0 Microscopes, care, use, staining techniques
2.6.0 Soldering, solders, fluxes
2.7.0 Tools for electrical experiments
2.8.0 Equipment for electrical experiments
2.2.0 Equipment care
2.2.1 Blueprints and diazo prints
2.2.2 Electrical outlets and equipment
2.2.3 Filtering
2.2.4 Fume cupboards, fume hoods
2.2.5 Gas installations and inspections
2.2.6 Gas-Pak
2.2.14 Prepare distilled water
2.2.7 Prepare sets of apparatus
2.2.8 Prepare stock materials and apparatus
2.2.9 Razor blades and knives
2.2.10 Stock control
2.2.11 Unpack, check and sort new equipment
2.2.12 Use safe practice and procedures
2.2.13 Water stills
2.3.0 Glass cutting, tubing, cleaning
2.3.1 Bend glass tubing
2.3.2 Cut glass tubing
2.3.3 Cut window glass with a straight cut
2.3.4 Glass cleaning
2.3.5 Cleaning agents, "chromic acid"
2.3.6 Cleaning agents, detergents
2.3.7 Cleaning agents, solvents
2.3.8 Insert glass tubing through a cork stopper
2.3.9 Potassium dichromate solution
2.3.10 Remove glass tubing from a stopper
2.3.11 Resistance wire glass jar cutter
2.4.0 Laboratory items
2.4.1 Beakers
2.4.2 Bosshead
2.4.3 Bottles, laboratory bottles
2.4.4 Bottle brushes
2.4.5 Burettes
2.4.29 Chromatography paper
2.4.6 Cork borers and sharpeners
2.4.7 Dissection kits
2.4.8 Drinking straws, soda straws, "straws"
2.4.9 Filter funnels
2.4.10 Flasks, borosilicate glass flasks
2.4.11 Hazard labels
2.4.12 Laboratory tweezers (forceps)
2.4.13 Measuring cylinders / graduated cylinder
2.4.14 Petri dishes
2.4.15 Pipettes
2.4.16 Porcelain, laboratory items
2.4.17 Retort stands, retort clamp
2.4.18 Screw clamp
2.4.19 Spatula
2.4.20 Stirrers, magnetic stirrers, hotplates
2.4.21 Stoppers, rubber stoppers
2.4.22 Test-tubes
2.4.23 Test-tube holder
2.4.24 Tongs
2.4.25 Tripod stands
2.4.26 Watch glass
2.4.27 Wire gauze mats
2.4.28 Timers, digital timers
2.5.0 Microscopes, care, use, staining techniques
2.5.1 Clean microscope slides and coverslips
2.5.2 Cut sections by hand
2.5.3 Microscopes and microscope accessories
2.5.4 Microscopes and sunlight
2.5.5 Microscopes in the tropics
2.5.6 Parts of a microscope
2.5.7 Prepare fresh material for microscope work
2.5.8 Stain onion epidermis
2.5.9 Use of a microscope
2.6.0 Soldering, solders, fluxes
2.6.1 Soldering
2.6.2 Solders
2.6.3 Flux
2.6.4 Methods of soldering
2.6.5 Soldering electrical connections
2.6.6 Torch soldering
2.2.1 Blueprints and diazo prints
It is sold as: "Sun Blueprint Paper".
A blueprint is a photographic print of a plan or technical drawing in white lines on a blue background.
1. Tape the edges and hinge two glass plates 25 cm by 35 cm along one long edge.
Put a sheet of blueprint paper, green side up, on one of the two glass plates.
Lay a flat object, e.g. a leaf, on the blueprint paper.
Hold the object in place with the second pane of glass.
Expose the plate to the sun.
Remove the blueprint paper and wash it with tap water to remove any remaining light sensitive substance.
Lay the blueprint paper on a smooth, flat table to dry.
2. Use the same procedure to make a diazo print, but after exposure to the sun do not wash the paper in tap water.
Instead, expose the blueprint paper to ammonia fumes in a large jar for several minutes, so that light can make no further changes on the blueprint paper.
(Diazo = bleaching action of ultraviolet radiation on diazonium salts)
3. Make blueprint paper.
In a dark room, dissolve 10 g of potassium ferricyanide in 50 mL of water and dissolve 10 g of ferric ammonium citrate in 50 ml of water.
Store the solutions in a dark cupboard.
In a dark room, mix equal volumes of the two solutions and place in a shallow tray.
Float a piece of paper on the mixture for a few seconds or solution or wipe the solution onto the paper with a soft brush.
Hang up the paper to dry in the dark room then store the blueprint paper in a dark place.
2.2.2 Electrical outlets and equipment
1. Permanent general purpose electrical outlets must be in a safe and operational condition.
New installations must be fitted with automatic blind outlets.
A qualified electrician should service and check all 240 V electrical equipment.
Equipment suppliers must supply schools with equipment that complies with government specifications, including appropriate earthing and use of approved insulating materials.
2. Electric current passing through the human body may cause breathing to stop, heart to stop, burns to the skin and internal organs, muscle spasm, clinical shock and falls that cause further injuries.
The danger depends on the value of the current and the body resistance.
The "let-go current" ("cannot let-go current") is the maximum current a person can tolerate when holding an electrode and still let go of this electrode using muscles directly stimulated by this current.
The value of this current is about 10 milliamperes.
Higher currents can cause muscle freezing that prevents the person releasing the hand from the conductor.
In Australia, the electricity reticulation system is MEN (Multiple Earth Neutral), i.e. the neutral wire is earthed at the powerhouse, at the point of supply to each consumer and at other points along the line between the powerhouse and consumer.
3. Electric shock may occur when a person contacts the active pin in a power point or switch or an exposed active wire in a lead.
For a touch voltage of 240 volts AC, the body resistance between its extremities is about 1000 ohms and the current flowing through the person would be 240 milliamperes causing serious results.
2.2.3 Filtering
See diagram 2.14: Folding filter paper.
Filter funnel, glass, 50 mm.
Filter funnel, polythene, 35 mm, pk 10.
Filter funnel, Buchner funnel, 52 mm diameter.
2.2.4 Fume cupboards, fume hoods
See diagram 1.13a: Simple fume hood.
Fume cupboards: Enclosed reinforced cupboard with facilities for chemical reactions and used under negative air pressure.
1. Do not use fume cupboards for long-term storage of any chemicals or as distribution areas for class sets of chemicals and equipment.
2. Most fume cupboards have an extraction fan mounted in the flue that conducts exhaust gases and vapours to the atmosphere.
Check the extraction fan regularly.
Heat-induced convection types of fume cupboards have a gas burner at the entrance to the flue to cause a rising convection current.
However, these units may be fire hazards if flammable gases or liquids are placed in the fume cupboard.
3. Fume cupboards should periodically be checked by competent safety authorities.
4. Fume cupboards provide a means of isolating hazardous gases and vapours from the classroom and dispersing them into the atmosphere.
Lock fume cupboard doors to prevent access to preparation and storage rooms from the teaching of science area.
Do not use fume cupboards for long term storage of any chemicals or as distribution areas for class sets of chemicals and equipment.
5.0 Types of fume cupboards with different methods of dispersal to the atmosphere.
5.1 Mechanical types of fume cupboards:
Most modern fume cupboards have an extraction fan mounted in the flue that creates sufficient exhaust gases and vapours to the atmosphere.
Service extraction fans periodically to remove any physical obstructions (e.g. birds' nests) and check on corrosion of the electric motor or fan.
5.2 Heat induced convection types of fume cupboards:
These older style units have a gas burner mounted permanently at the entrance to the flue.
When alight the hot gases cause a rising convection current that draws the hazardous gas or vapour through the flue.
These units pose a significant fire hazard when flammable gases or liquids are placed in the fume cupboard when the burner is alight.
Do not attempt to use the burner in these fume cupboards.
5.3 Diffusion types of fume cupboards:
A fume cupboard may have a simple flue that allows dispersal of gases and vapours by molecular diffusion.
This type of unit cannot be used to disperse gases that are heavier than air.
They will accumulate in the bottom of the unit and slowly leak back into the classroom.
These units are not acceptable for use in gas dispersion.
2.2.5 Gas installations and inspections
1. Gas bottles (9 kg or less).
The school is responsible for maintaining and filling these cylinders, and for having them tested after they are ten years old.
It is illegal for a refilling station to refill cylinders older than 10 years that have not been tested again.
2. Permanent gas installations.
These include laboratories supplied with large 45 kg cylinders of LPG or connected to natural gas or town gas.
They should service all permanent installations annually.
In this service, turrets, control valves and cylinders are checked for correct operation and leaks.
The age of cylinders is also checked.
If they are found out of date, the contractor will check with the school for the date of the last refill.
If we have not refilled the cylinders for some time, they will ask the school to organize a refill whether the cylinders are empty or not.
3. Cylinders may be refilled on site or replaced.
It is the refiller's responsibility to check the date on your cylinder and provide cylinders that are current.
4. Isolation valves.
Turn all gas off when not in use.
Areas for the teaching of science with permanent gas are fitted with isolation valves.
These may be manual, or an electronic keypad controlled, isolation valves.
All personnel who are using rooms equipped with reticulated gas supply should familiarize themselves with the various methods of isolating gas, when not in use.
2.2.6 Gas-Pak
See diagram 2.11 Gas-Pak.
Be careful! The gas forms an inflammable mixture with air.
The Gas-Pak consists of a burner connected to a small disposable can of gas.
Instructions for use.
1. Remove the cap from the Gas-Pak can.
With the control knob in the "off" position, push the plug-in valve firmly onto the can.
Close the sleeve holes.
Light a match.
Turn the control knob slowly to the "on" position until gas flows.
Light the burner.
Adjust the gas control knob and sleeve on the burner.
2. If the flame is poor, check the gas content of the can, check that the plug-in valve is seated correctly, adjust the gas control knob.
3. If the flame is still poor, turn off the gas and wait for the burner to cool.
Unscrew the burner head on the gas.
Use the jet pricker wire to clear the jet by inserting the pricker wire into the jet hole and moving it up and down until the jet is clear and the gas flow is normal.
Relight the burner as above.
4. Use the burner only in a draught free area.
Always keep the can upright when the burner is alight.
Check any warnings on the can.
Allow the burner to cool before you move or store it.
Dispose of Gas-Pak cans safely, i.e. do not puncture or incinerate them.
5. Do not turn the gas on without lighting the burner.
Do not heat low melting point objects directly over the barrel of the burner, e.g. plastics, solder, lead, because pieces may fall inside the barrel of the burner.
Instead, hold the burner at an angle to the barrel.
2.2.7 Prepare sets of apparatus
1. Consistent use in daily laboratory activities, e.g. glassware sets.
2. Occasional use in demonstrations, or in rotation by student groups.
3. Individual student use.
Issue some equipment from the store in the laboratory as permanent issue.
Issue other equipment daily from stock.
4. Sets for everyday use, e.g. glassware, measuring devices, basic chemicals.
These sets must be established and maintained as breakage and usage reduce the basic stock.
5. Sets for demonstrations.
Partially or wholly assembled equipment may be gathered and stored in a suitable location with a label showing the relevance of the material, e.g. physics apparatus for demonstrating the Bernoulli effect.
6. Sets for issue.
Many items are normally kept separate and assembled by the student as they are issued from the store, e.g. batteries, terminals and leads.
However, student kits for particular experiments are frequently stored as complete sets.
Materials from these sets should not be "borrowed" for other experiments.
2.2.8 Prepare stock materials and apparatus
1. Lengths of insulated copper wire with bared ends, or with alligator clips screwed to the ends, or with 4 mm plugs attached to the ends.
2. Standard coils, using cardboard or polythene cylinders as the core.
3. Simple wood baseboards with terminals, for making simple circuits.
4. Atomic and molecular kits into a predetermined order.
5. Collection of raw materials.
Acetate or cellophane squares, e.g. red, yellow, blue, agar jelly or gelatine, aluminium foil,
balance spring, bicycle pumps, bottles, brass gauze, brass sheet, bronze mesh, brass pins
candles, cardboard squares, clothes pegs, copper wire, copper sheet, copper turnings, corks, cork slabs, cotton reels, cardboard cylinders, chalk boxes,
dry cells, drinking glass,
fibreglass, fly screens, flannel rags, fencing wire,
G-clamp, grease-proof paper,
hacksaw blades, hand drill, hand tools,
iron filings, iron nails, iron pins, iron filings,
jam tins with press-on lids,
lubricating oil and grease, olive oil, metal sheets, metal pulley wheels, marbles, mirrors,
needles,
olive oil,
plastic lenses, ping-pong balls, pith, plastic rulers, plastic containers, paste, Plasticine (modelling clay, plastilina),
razor blades, rubber balloons, rubber bands, rubber balls, olive oil, suction cups, silk pieces, sewing needles, screw eyes, springs,
thread, thermometers, torches, table forks, tin snips.
2.2.9 Razor blades and knives
See diagram 2.10 Good and bad razor blades.
Use single edge razor blades, e.g. "Gem" brand, instead of the usual double edge razor blades.
Students find single edge blades easier to use, and they are less likely to cut themselves.
Teach students to always cut in the direction away from the body.
Use knives by cutting down on the bench.
Reduce the use of knives and razor blades by giving the students precut material.
At the end of the class check that all razor blades and knives have been returned.
2.2.10 Stock control
1. Every science department must have two stock books, one for consumable chemicals and one for apparatus and other hardware.
On taking over a laboratory, check the stock books to ensure: a stocktakel was done in the previous year, the stock as listed is correct.
Store equipment or chemicals immediately after use.
Have a designated place for each type of item.
Leaving equipment out on benches invites pilfering or breakage.
Keep a breakage book in the science room and enter all breakage as soon as practicable after they occur.
This is essential if you are to account for all apparatus at the next stocktakel.
2. When new stock arrives, enter the quantity and the date of receipt in the appropriate columns in the stock records.
Store separately any broken or unserviceable equipment other than glassware, rubber stoppers and tubing, or plastic ware.
During stocktakel all equipment should be inspected by the stocktakelr and any damaged, unserviceable or potentially dangerous equipment put aside.
This is especially necessary with equipment handled by students.
Test-tube holders, beaker tongs, and stands should all be checked, and new items ordered if any are defective.
Never allow chipped or cracked glassware to be used.
2.2.11 Unpack, check and sort new equipment
1. When equipment arrives, it must be unpacked in a location that allows the materials to be set out and checked against the enclosed invoice.
Any discrepancies or breakage should be noted and the supplier notified.
Enter the quantity and date of receipt in the appropriate columns of the stock records.
2. Some materials will act as replacements while other items will need storage space assigned to them.
Items of "short life", e.g. dry cells, should be date-stamped before storage.
Consumable stock, e.g. chemicals, should be date-stamped before storage to reduce possible wastage of those chemicals that may deteriorate with storage.
Annotate the label with a felt pen to show the year of supply.
Store stock, e.g. chemicals, with oldest stock in front to reduce wastage.
Items marked "to follow" on invoices will be supplied when obtainable, unless schools signify that they are no longer required.
2.2.12 Use safe practice and procedures
1. Dry hands thoroughly before operating any switch.
2. Do not remove the cover plates of power points or switches.
If the cover plate has been removed or damaged, do use it until repaired by a qualified electrician.
Do not attempt to repair a power point or switch yourself.
Do not attempt to repair mains-operated equipment, e.g. hot water systems, ceiling fans, refrigerators.
3. Switches must be in the "off" position before inserting plugs or removing plugs from power points.
4. When removing plugs from power points, grasp the plug firmly and pull.
Do not pull on the lead.
5. Do not let students push metal objects into power points or poke at pilot lights with metal objects.
6. Hand-held equipment, e.g. electric drills, unless double insulated, must be operated through an isolating transformer or a core balance earth leakage device to protect the operator from injury if the earth connection is faulty.
7. Avoid using 240 volt equipment near sinks or water outlets or close to gas outlets where accidental sparking may ignite gas leaks.
8. Disconnect portable appliances from the power outlet when not in use or before cleaning.
9. When connecting several appliances to the mains, use power boards, not double adapters.
10. Inspect all leads for frayed or cracked insulation.
Do not knot or sharply bend leads or nail leads to the wall.
Under the current Australian Standard International Standard the "live lead" is red to brown, the "neutral lead" is black to blue, the "earth lead" is green or yellow.
The "earth lead" is to earth the metal case of equipment to prevent shock to the user should a short circuit occur between the electrically "live" parts of the equipment and the metal case.
The other two wires carry the electric current operating the equipment.
2.2.13 Water stills
A potential exists if stills do not have an automatic power supply cut-off in case of failure of the water supply.
If the water supply fails, the unit may overheat and cause a fire.
Most models produced in the last 10 years have automatic cut-off switches fitted.
These switches should be periodically checked.
Do not operate stills overnight or leave unattended for long periods during the day.
2.2.14Prepare distilled water
See diagram 23.32: Prepare distilled water.
A kettle can be used to provide steam, which is then condensed in a jam jar fitted with a large cork and immersed in a pan of cold water.
Rubber tubing, adhesive tape or clay can be used to make the joint.
2.4.1 Beakers
Glass beakers, squat, borosilicate glass, suitable for heating, 50 mL, 100 mL, 250 mL, 600 mL, 1000 mL, 2000 mL, box / 10
Polypropylene beakers, opaque, unsuitable for heating, 250 mL, 500 mL, 1000 mL, 2000 mL
Polypropylene jug, opaque with handle, 2000 mL
Sample cups, disposable, clear plastic, 35 mL, pack / 200
Sample cups, disposable, pleated paper, 104 mL, pack /100
2.4.2 Bosshead
Bosshead, supports up to 20 mm rods, Commercial
Heavy duty, die cast alloy, nickel plated screw head, support rods to 20 mm diameter.
2.4.3 Bottles, laboratory bottles
Droplet bottles, polyethylene, clear bottles, Stuhl cap and seal, 50 mL, 125 mL
Droplet bottles, glass dropper with screw cap and plastic teat, 50 mL, amber, clear
Droplet bottles, Dropping assembly only
Laboratory bottles, borosilicate glass, non-drip, non-leak, non-venting durable cap, 250 mL, 500 mL, 1000 mL, 2000 mL
Reagent bottles, glass, narrow mouth with plastic stopper, 250 mL, 500 mL, box / 6
Reagent jars, glass, wide mouth, plastic screw cap, 60 mL, 250 mL, 500 mL
Sample vials, plastic, screw-on cap, 27 mm diameter × 80 mm height
Specimen jar, plastic, clear, stackable, screw-on lid, 65 mm diameter × 80 mm depth
Wash bottles, plastic with spout, Kartel 1633 integral with nozzle, 250 mL, 500 mL
2.4.4 Bottle brushes
Bottle brush, 17 mm diameter, 50 mm brush, 150 mm overall length
Bottle brush, 25 mm diameter, 75 mm brush, 200 mm overall length
2.4.5 Burettes
See diagram: 1.26 Burette.
Titrate dilute hydrochloric acid with sodium hydroxide solution, with a burette: 12.8.4.0.
Titrate dilute hydrochloric acid with sodium hydroxide solution, with a burette (second method): 12.8.4.1.
Glass, with Teflon tap, 50 mL, removable stopcock.
Glass, with Teflon tap, 50 mL, straight stopcock, 0.1 mL graduations, non-detachable nozzle.
Plastic, 50 ml (Not for use with organic solvents).
Burette clamp, double, metal, fisher type, with boss head.
Burette clamp, double, aluminium, plastic covered spring jaws, up to 25 mm diameter, support rod 13 mm.
2.4.6 Cork borers and sharpeners
Cork borerss, set of 12, non-serrated, cork or rubber stoppers, Commercial
Serrated borers for cork or rubber stoppers, set of six borers (5 mm to 12.5 mm), push rod.
Non-serrated borers for cork or rubber stoppers, set of twelve (5 mm to 21.5 mm), push rod, can be sharpened.
Sharpener, aluminium cone, hardened steel blade, for non-serrated borers diameter up to 27 mm.
See diagram Set of cork borers
Use of a cork borer
NEVER hold a cork in one hand and use the other hand to insert the cork borer into the cork.
Hold the cork firmlyon the laboratory table and press the cork borer down onto the cork.
Cork borers may also be used to take sample of living wood fo rtree ring analysis and taking samples of micobiology agar gel for microscope inspection of the gel.
Cork boring machines are available.
See: 2.3.8 Insert glass tubing through a cork stopper
See: 2.3.10 Remove glass tubing from a stopper
2.4.7 Dissection kit
1. Dissection kit containing scalpel, forceps, probes, scissors in zippered case.
2. Scalpel blades, sterile, suits handle number 4.
3. Scalpel handle.
4. Scalpel blade remover.
2.4.8 Drinking straws, soda straws, "straws"
White paper drinking straws, polystyrene straws (denser than water), polypropylene straws (less dense than water), articulated straws (bendable straws, hinged straws, "Bendy straws"), bio-flex straws, (bioplastic straws), bamboo straws, glass straws, stainless steel straws.
Drinking straws, regular, 200 mm, pack / 250, plastic, pk 1000.
Use drinking straws to unclog opened ketchup bottle, blow bubbles, extend oil can spout, can lengthen flower stems, substitute eyedropper, mark a knitting stitch, gather wires in a conduit.
Experiment
12.1.18 Drinking straw, finger on drfinking straw. glass tube.
2.4.9 Filter funnels
Filter funnels, polyethylene, 75 mm
Filter funnels, soda glass, 1000 mm
2.4.10 Flasks, borosilicate glass flasks
See diagram 3.2.75.2: Erlenmeyer flask, (conical flask).
See diagram 12.1.04: Round-bottom flask.
Conical flask, Erlenmeyer flask (flat bottom, conical body, cylindrical neck), 100 mL box /10, 250 mL, box /10.
Volumetric, with polyethylene stopper, 100 mL, 250 mL, 500 mL, 1000 mL.
2.4.11 Hazard labels
Hazard stickerss Commercial
Diamond shaped adhesive labels, 20 mm × 20 mm
OXIDISING AGENT, roll / 250
FLAMMABLEFl, roll / 250
TOXIC, roll / 250
CORROSIVE, roll / 250
2.4.12 Laboratory tweezers (forceps)
Make tweezers from the flexible strap iron used to put around boxes for shipment.
The tweezers shown are about 12 cm in length.
One pair shown in the diagram can be made by brazing or riveting two pieces of strap iron together, then bending and cutting to the proper shape.
The other pair shown were fashioned from a single 25 cm length of strap iron.
The round head was made by pinning the centre of the strip around an iron rod of suitable diameter.
The sides were then cut and shaped to size.
2.4.13 Measuring cylinders / graduated cylinder
Select several straight sided glass jars of assorted sizes.
Olive bottles are very useful for the making of graduated cylinders.
Paste a strip of paper about 1 cm wide vertically on the outside the bottle to within about a centimetre of the top.
Obtain a graduated cylinder of the same capacity as the bottle, pour enough water from it to fill the bottle nearly to the top of the paper scale.
Draw a line across the paper scale and mark under it the number of cubic centimetres of water poured in.
Repeat with lesser amounts of water to complete the scale.
Industrial website products:
Glass measuring cylinders: 25 mL 0.5 mL graduations, 100 mL 1 mL graduations, 250 mL 2 mL graduations, 500 mL 5 mL graduations, 1000 mL 10 mL graduations.
Polypropylene measuring cylinders with fixed base: 10 mL 2 mL graduations, 25 mL 1 mL graduations, 50 mL 2.5 mL graduations, 100 mL 5 mL graduations, 250 mL 5 ml graduations.
2.4.14 Petri dish
See diagram 9.4.10: Taped Petri dish.
Disposable, 90 × 14 mm, clear polystyrene, heat resistant to 80oC, pack / 20 (also gamma sterilized).
2.4.15 Pipettes
Battery-operated pipette filler
Glass or plastic pipettes, 25 mL
Disposable plastic Pasteur pipette type with attached bulb, 150 mL, 1 mL graduations, bulb draw of 3.1 mL
Pipette accessories
Pipette filler, rubber ball type
Pump, 25 mL, to fit straw type pipettes
Dangers of using pipettes in the laboratory
Fill pipettes with a pipette-filler and not by sucking by mouth.
Glass pipettes can cause lacerations to the hands of operators.
Using the mouth to operate a pipette is prohibited in school laboratories, so pipette aids, fillers and pumps must be used to allow users to avoid mouth contact with chemicals and biological materials.
However, injuries may occur when a glass pipette is being inserted into a pipette filler or when placing the rubber bulb onto a glass Pasteur pipette, ready for use.
Alternatives to pipettes include pipettes that use a plastic disposable tip to dispense volumes to 5 ml and repetitive dispensing from a single bottle of a solution using a dispenser.
Polycarbonate pipettes can be used to replace glass bulb and graduated pipettes.
Disposable polyethylene Pasteur pipettes can be used in place of glass Pasteur pipettes.
Disposable polyethylene Pasteur pipettes are moulded as one piece with the bulb incorporated into the body of the pipette, so it is not necessary to purchase separate bulbs.
A rubber pumpette that inserts into the end of the pipette and has no valves has no recorded pipette breakage.
However, this type of pipette aid is not suitable for pipettes that have a cotton wool plug.
Automatic pipette pumps can be used to replace pipette aids.
A pipetting station utilizing an electrically-operated or battery-operated pump can be set up to service several students.
2.4.16 Porcelain, laboratory items, Crucibles, Evaporating basin
Porcelain is a kaolin, quartz and feldspar mixture, heated to over 1, 300oC.
Evaporating Dish, evaporating basin, Commercial
Mortar and Pestle Commercial
Porous Pots Commercial
Spotting Plates Commercial
Crucibles with lid, 30 mL Commercial
Mortar and pestle 10 mm Commercial
Spotting tile, 12 depressions, 110 mm × 90 mm Commercial
Evaporating basin, bowl shape, 75 mL Commercial
2.4.17 Retort stand, retort clamp
Retort stand, 600 mm rod, with clamp and boss head, 150 mm × 250 mm base
Metal retort stand clamp, three prong, suits 5 mm to 90 mm diameter objects
Boss head, to fit 9 mm and 12 mm retort stands
Retort ring, with arm 70 mm, with fixed angle boss head, made of zinc-plated steel, 75 mm
2.4.18 Screw clamps
Screw clamp, Hoffman type, 20 mm, opening with hinged bottom, nickel-plated brass
2.4.19 Spatula
Spatulas, stainless steel, rice grain type, 8 mm × 5 mm spoon, 140 mm length Spatulas, stainless steel, double-ended, 8 mm width, 150 mm length
2.4.20 Stirrers, magnetic stirrers, hotplates
Stirring rod, PP 248 mm, polypropylene Commercial
IEC Magnetic stirrer and hotplate, with "Simmersat" temperature control, front panel mains switch, heat control and speed control, for stirring, regular high temperature alloy hot plate, 200 mm ×100 mm.
16.7.18 Iron from breakfast cereal, (magnetic stirrer).
6.7 Lactophenol cotton blue (magnetic stirrer).
3.4.11 Prepare slime balls (magnetic stirrer).
12.1.11 Rainbow reactions (magnetic stirrer).
Stirring rod, glass 6 mm outside diameter, 150 mm.
Stirring rod, glass 6 mm outside diameter, 300 mm.
2.4.21 Stoppers, cork stoppers, rubber stoppers
See diagram 2.8: 2-hole rubber stopper
Premium grade cork stoppers function as a closure for bottles, vials, laboratory and other openings.
They have fewer lenticels (crevices) than standard grade.
This means they are better suited for use as laboratory corks and for transporting many kinds of liquids.
Cork Stoppers are safe to 150oC,.
Many sizes are available to plug openings from 1/8" up to 2".
All our cork stoppers are made from 100% natural cork.
Sizes: 0000 000 00 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 22 24 26 28
Rubber stoppers, diameter measurement for the bottom, 10 mm, 13 mm, 16 mm, 18 mm, 19 mm, 22 mm, pack /10
Rubber stoppers, diameter measurement for the bottom, 25 mm single hole, pack /10
2.4.22 Test-tubes
Test-tubes, glassware and microscope slides: 3.3.1 Safety
Test-tubes, borosilicate glass with rim, 12 mm × 100 mm, box /100
Test-tubes, borosilicate glass with rim, 25 mm × 200 mm, box /100
Test-tubes, borosilicate glass with rim, 18 mm × 150 mm, box /100
Test-tubes, borosilicate glass with rim, 18 mm × 180 mm, box /100
Test-tubes, borosilicate glass with side arm, 12 mm × 100 mm, box /100
Test-tube brush, pk 10
Test-tubes, Pyrex with rim, 25 mm × 200 mm, box /50
Test-tube, "Pyrex" 75 × 10 mm, pk 100
Test-tube and burette brushes, 15 to 20 mm diameter × 50 to 250 mm + 30 mm long bristle tip
Test-tube clamps., metal, Stoddard type, with finger grips, nickel-plated steel, 13 cm length
Test-tube clamps, brass with wooden handle, safe with open flames, 22.5 cm length
Test-tube clamps, wooden strong spring, for < 19 mm diameter test-tubes, 17.8 cm length
Test-tube holder, wood, spring, pk 10
Test-tube holder, plated spring steel wire, holds up to 30 mm test-tube
Test-tube racks, polypropylene, holds 40, suits 20 mm test-tubes, suit 25 mm test-tubes
Test-tube racks, wooden with six holes and pegs, holds 25 test-tubes
Test-tube, sidearm, borosilicate glass, 125 mm, pk 10
Test-tube, soda glass, 50 × 10 mm, pk 250
Test-tube, soda glass, 100 × 16 mm, pk 100
Test-tube, stand, 6 hole, no peg
Test-tube, small test-tube, ignition tube, borosilicate or Pyrex, heat resistant glass, 75 × 8 mm, pk 100
Test-tube, medium test-tube, borosilicate or Pyrex, heat-resistant glass, 150 × 15 mm, pk 100
Test-tube, large test-tube, boiling tube, borosilicate or Pyrex, heat-resistant glass, 150 × 25 mm, pk 100
2.4.23 Test-tube holder
Clamps Commercial
Make a test-tube holder by bending into shape strong spring wire, e.g. wire from a coat hanger.
2.4.24 Tongs
Beaker tongs, stainless steel with rubber grips, for 50 mL to 2000 mL beakers
Crucible tongs, brass metal, 200 mm
2.4.25 Tripod stands
Tripod stand, triangular, 200 mm high, 125 mm side
Tripod stand, stainless steel, 200 mm high, 130 mm side, rubber feet
Tripod mesh mat, stainless steel (cannot fall off stand or be caught in cuffs)
2.4.26 Watch glass
Watch glass, soda glass watch glass, ground edge, 125 mm diameter.
2.4.27 Wire gauze mat
Wire gauze mat, 150 mm square, plain fine mesh, folded edges
Wire gauze mat, 150 mm square, non-asbestos clay centre, folded edges
Gauze mat, mesh, galvanized iron 12.5 × 12.5 cm
Gauze mat, stainless steel, 15 × 15 cm
2.4.28 Timers, digital timers
Time pendulums, stopwatch, ticker timers, Commercial
Digital timer, Counts up and down, accurate to one second, alarm
Digital timer, four channels, counts up and down, accurate to one second, with clock
2.4.29 Chromatography paper
Chromatography paper, Bonnett, 1518 Grade 1CHR, 200 mm × 200 mm, pack / 100
2.3.3 Cut window glass with a straight cut.
See diagram 2.15: Cut glass with straight cut
1. To cut window glass and Perspex (Lucite), with a straight cut.
A glass cutter does not cut glass.
It splits the glass with a tiny wheel.
A glass cutter makes a scratch or groove by crushing the surface the glass.
The sides of the glass cutting wheel act as wedges to push against the sides of the groove and start a small crack.
Experiment
Practise on scrap glass to get the pressure needed for a smooth edge.
If a crack fails to start, tap the scratch or score with the ball end of the glass cutter.
2. Perspex (Lucite), polymethyl methacrylate, is a hard plastic material, so it is not difficult to cut it with a hacksaw, but it is not easy to cut it straight.
Scribe the surface with a broken hacksaw blade.
Place it on a tabletop and align the scratch or score with the rim of the table.
Press the part on the table with your hand and quickly hit the other side of the Perspex in the air so that it separates cleanly along the scratch.
3. If the glass cutter wheel is sharp and it is drawn over the glass at the right speed and pressure, it makes a fine score or groove by slightly crushing or pulverizing the glass.
The bevelled sides of the wheel act as wedges that push against the sides of the groove and pry the glass apart so that a crack is started.
Practise on scrap glass to get the pressure needed for a smooth edge.
Before trying to make a finished cut, practise on a scrap piece to learn the speed and pressure required to obtain a smooth edge.
Ordinary window glass comes in two thickness, single light and double light.
Single light glass is thinner and easier to cut.
Plate glass up to 0.6 cm in thickness can be cut in the same manner as ordinary window glass.
Safety glass that consists of two or more glass sheets cemented together by a transparent plastic, requires special cutting equipment.
2.3.2 Cut glass tubing
Glass tubing cutter, up to 38 mm diameter Commercial
See diagram 2.16 Break or bend glass tubing.
Experiment
Use glass tubing, 6 mm outside diameter, 750 mm length.
Use plastic tubing, clear, 8 mm inside diameter, 30 metre roll.
1. One way to cut glass tubing is to score the surface with one forward stroke of a three cornered file.
Make the score mark at right angles to the centre line of the tube so that the tube will snap squarely across.
To snap the tube, place it on the bench top with matchsticks or toothpick directly beneath the upward facing score mark.
Then, holding one end securely, press down on the other end and the snap will be immediate.
2. Another method used is to scratch the glass tubing with a quick smooth file stroke, then hold the scratched tubing firmly in both hands with thumbs pointing towards each other, but on opposite sides of the scratch, and snapping the glass tubing away from this body.
Fire polish the cut ends.
3. The method of cutting a glass tube depends on its diameter.
Different methods are used to cut glass tubes of different diameters.
Place the tube flat on the table.
Measure the required length.
Hold the tube firmly and draw a triangular file across it a couple of times so that a scratch is made.
Do not saw back and forth.
One or two firm cuts are usually sufficient.
Take the tube in both hands, one each side of the scratch.
Keep your thumbs as close as possible to the scratch.
Press gently with your thumbs and pull with the fingers.
The two pieces of tubing should separate.
Brute strength is not needed.
If the tube does not break easily, make the file scratch a little deeper and longer.
Fire polish the cut ends.
Light the burner, and open the air hole.
This gives a hot blue flame.
Warm one end of the tubing by passing it through the flame a few times.
When the tubing is warm, rotate the end of the tube in the flame until the glass begins to turn yellow and melt a little.
Keep rotating the tube until the rough edges become smooth.
Do not heat too much and do not stop rotating.
Place the hot glass on a gauze mat to cool.
The end is now fire-polished.
When the tube is cool, fire polish the other cut end.
Again leave to cool.
4. Place the tube flat on the table.
Measure the required length.
Hold the tube firmly and draw a triangular file across it a couple of times so that it makes a scratch.
Do not saw back and forth.
One or two firm cuts are usually sufficient.
Take the tube in both hands, one each side of the scratch.
Keep your thumbs as close as possible to the scratch.
Press gently with your thumbs and pull with the fingers.
The two pieces of tubing should separate.
Do not use brute strength.
If the tube does not break easily, make the file scratch a little deeper and longer.
5. Fire polish the cut ends.
Light the burner, and open the air hole.
This gives a hot blue flame.
Warm one end of the tubing by passing it through the flame a few times.
When the tubing is warm, rotate the end of the tube in the flame until the glass begins to turn yellow and melt a little.
Keep rotating the tube until the rough edges become smooth.
Do not heat too much and do not stop rotating.
Place the hot glass on a gauze mat to cool.
The end is now fire polished.
When the tube is cool, fire polish the other cut end.
Again leave to cool.
Put all broken glass in a special labelled container, not in the waste paper basket.
6. Seal the end of a thin glass tube.
Place the glass tube at the top of the hot blue flame of the Bunsen burner, because the flame is the hottest there and rotate the tube to heat it uniformly.
Note that the part being heated is some part at the middle of the glass tube, not its end.
When the part being heated becomes hot and soft, clamp the two ends of the tube and pull the tube outwards so that the part being heated.
It becomes thin into a capillary.
If go on pulling, the thinnest part will fall down. So the original tube will become into two tubes and their ends have been sealed, or have became very thin.
Place one end of the tube at the top of the hot blue flame of the Bunsen burner and rotate it during heating it until the end is sealed completely, and it becomes very smooth.
Leave the tube off the flame and blow the inside of its open end while it is hot to make the end sealed smoother.
Stress relief the sealed end by gently heating, but do not soften the glass.
7. Seal the end of a thick glass tube.
Place one end of the glass tube at top of the hot blue flame of the Bunsen burner, where the flame is the hottest, and rotate the tube to heat it uniformly.
When the end is soft, lower the cool end so that the heated end is at the top.
Keep rotating and heating until the glass at the end heated becomes soft and flows into the tube so that the end is sealed completely.
2.3.1 Bend glass tubing
See diagram 2.16: Break or bend glass tubing.
Attach a flame spreader to the barrel of the Bunsen burner.
Light the burner and open the air hole to get a hot blue flame.
Using both hands, move the glass tubing back and forth through the top of the flame while rotating the tubing.
Heat about 5 centimetres of tubing.
When the tubing is warm, lower it into the dark blue cone of the flame.
Keep rotating the tubing until it glows red and becomes soft.
Take the tubing out of the flame and bend it slowly and steadily.
Do not force the bending and once bent do not reheat the tubing.
Keep holding the tubing until it starts to cool then put it on the gauze mat to cool to room temperature.
2.3.4 Glass cleaning
Glassware should be clean and dry before use.
When an experiment is completed, the students should discard leftover materials, and rinse all glassware in water.
Cleaning is best done immediately after use as this prevents the staining of work surfaces and the hardening of materials on the glass.
Strong cleaning solvents should be used by the teacher, not by students.
2.3.5 Cleaning agents, "chromic acid"
Safety Glasses Commercial
See diagram 1.13a: Simple fume hood.
Be careful! Use safety glasses and nitrile chemical-resistant gloves in a fume cupboard, fume hood.
If you splash chromic acid on your skin, wash it off immediately, with plenty of water.
This fluid will corrode skin and clothing.
Wear protective clothing.
Dissolve 10 g potassium dichromate in 50 mL water.
Add concentrated sulfuric acid very slowly, stirring, until the volume is 200 mL.
Leave to stand for 10 minutes in a fume cupboard, fume hood.
Add another 800 mL of concentrated sulfuric acid, constantly stirring and cooling in an ice bath.
Pour chromic acid into empty, dirty glassware and leave for 10 to 30 minutes.
You may reuse this chromic acid, but discard it when its colour is greenish.
BE CAREFUL! Use gloves and fume cupboard.
If you splash chromic acid on your skin, wash it off immediately, with plenty of water.
This fluid will corrode skin and clothing.
Wear protective clothing!.
2.3.6 Cleaning agents, detergents
Soak glassware in hot water with detergent.
Put liquid or powder detergent into the apparatus, add hot water and scrub with a bottle brush or a scourer.
Rinse the glassware with hot water.
Rinse with distilled water if cleaning pipettes, burettes and volumetric flasks.
Detergents are simple to use, but very hard to remove.
Do not use abrasives that scratch the glass.
2.3.7 Cleaning agents, solvents
Be careful! Ethanol, propanone and ether are highly flammable.
Extinguish all burners and gas heaters before using them.
Solvents are very useful if we know that the material to be removed is readily soluble in one or in a mixture of these solvents.
The following commonly used solvents should never be used in a practical class, but may be used in a preparation room:
4.1 Ethanol (ethyl alcohol)
4.2 Propanone (acetone)
4.3 Xylene, do not pour into the sink, keep and discard with wastes.
4.4 Hexane, do not pour into the sink, keep and discard with wastes.
4.5 Petroleum ether, do not pour into the sink, keep and discard with wastes.
Dry glassware after cleaning.
Air dry glassware on racks.
Rinse in ethanol, propanone or ether and blow air through the vessel.
Dry beakers, pipettes, and flasks in an oven at 110oC, after rinsing in water.
BE CAREFUL! Ethanol, propanone and ether are highly flammable.
All burners and gas heaters should be extinguished before using these flammable chemicals!.
Glass cleaning safety
Strong cleaning solvents should be used by the teacher, not by students.
Dissolve 100 g potassium dichromate in a solution of 100 g concentrated sulfuric acid in 1 litre of water.
Glassware can be soaked in the solution, which may be used repeatedly again.
Be careful! Take great care to avoid getting this very corrosive solution on skin or clothes.
When diluting concentrated sulfuric acid, use a stone or earthenware vessel.
Pour the acid very slowly into the water, as a great amount of heat is given out in the process.
The teacher should use his knowledge of chemistry to remove stains of known origin.
If dirty vessels have contained alkalis, or salts with alkaline reactions, then the cleaning effect of a little dilute acid should be tried first.
If the stain is due to potassium permanganate, then the effect of sodium sulfite solution, acidified with dilute sulfuric acid should be tried.
Alkalis slowly attack glass, and bottles that have contained caustic soda for a long time will never recover their original transparency.
2.3.8 Insert glass tubing through a cork stopper
See diagram 2.18 Insert glass tubing through a stopper.
Be careful! Inexperienced teachers and students should not attempt this procedure.
1. Method A.
Check that the tubing will fit into the one-hole stopper.
The ends of the tubing should be fire polished with no sharp edges.
Wet the tube and the stopper with water containing a little detergent.
This makes them slippery and s easier to get the tube through the stopper.
Use the cloth to hold the tube firmly.
Place a leather gardening glove on the hand that will hold the stopper.
Slowly rotate the stopper on the tube.
Keep wetting the stopper and tubing so that the tube slides easily.
Be careful! Never hold the palm of the hand over the end of the test-tube.
2. Method B.
Lubricate the glass tubing with glycerol or water.
Wrap glass tubing in a towel.
Hold the glass tubing with the towel, then push it through the stopper with a twisting motion.
3. Method C, Safer methods that use cork borers.
To insert glass tubing, or a thermometer, through a stopper, if the glass tubing is not a wide bore, then select a cork borer that is just wider than the glass tubing.
Push the cork borer through the hole in the stopper using a twisting action.
For wide bore glass tubing, push a smaller size cork borer through the stopper from the opposite side.
Use the next larger size borer and push this over the cork borer already in the stopper from the other side.
Use a twisting action to push it between the cork borer already in place and the stopper.
When the correct size cork borer is in place in the stopper, slide the glass tubing or thermometer into place within the stopper.
Then pull out the cork borer with a twisting action to leave the glass tubing or the thermometer in place.
3.1 Cork stoppers should be rolled before using to make them soft so that they can be inserted into a bottle easily.
Also, it is also easier to drill a hole through a rolled stopper.
3.2 Drill a hole on a stopper.
Sharpen the edge of a drill with a steel file.
Drill with only a slight force so the drilling can be corrected in case the drilling is off the centre.
Use water as lubricant for a cork stopper and alcohol for a rubber stopper.
For cork stoppers, the drill diameter should be slightly smaller than the diameter of the glass tube that will be inserted, because the cork has poor elasticity.
For rubber stoppers, the drill diameter should be the same as the glass tube to be inserted.
3.3 Fit a glass tube through a cork.
Spread water on the surface of glass tube for lubricating.
Cover the tube with cloth or put on thick gloves to protect hands.
Insert the tube into cork with the tube tightly held to reduce the possibility of tube breaking.
2.3.9 Potassium dichromate solution
Dissolve 100 g potassium dichromate in a solution of 100 g concentrated sulfuric acid in 1 litre of water.
Soak glassware can be soaked in this solution.
It may be used again repeatedly.
Be careful! Avoid getting this very corrosive solution on skin or clothes.
When diluting concentrated sulfuric acid, use a stone or earthenware vessel.
Pour the acid very slowly into the water, because a great amount of heat is given out in the process.
If dirty vessels have contained alkalis, or salts with alkaline reactions, first try the cleaning effect of a dilute acid.
If the stain is due to potassium permanganate, try using sodium sulfite solution acidified with dilute sulfuric acid.
Alkalis slowly attack glass, so bottles that have contained caustic soda for a long time may never recover their original transparency.
2.3.10 Remove glass tubing from a stopper
1. Method A: To remove the tubing from the stopper, cutting the stopper is probably the safest method.
However, you can keep the stopper with glass tubing inserted for any future use.
2. Method B: To remove glass tubing from a stopper, select the cork borer that just fits over the glass tubing.
Push this over the tubing and with a twisting action push this between the glass and the stopper.
Continue to rotate the cork borer and push it through the stopper.
Pull out the glass tubing.
Pull out the cork borer.
2.3.11 Resistance wire glass jar cutter
See diagram 2.21, Resistance wire glass jar cutter.
Be careful! Use safety glasses and thick gloves.
Use 60 cm of 24 gauge nichrome wire, and make heat proof handles, one with a switch, for the ends.
Connect to a 12 volt 5 amp power supply, e.g. a car battery or a step-down transformer.
The wire should become red hot a few seconds after switching on.
Reduce the length of the resistance wire if it still does not get hot enough.
Use a triangular file to make a small groove on the glass jar where the nichrome wire will cross.
Adjust the wire in a loop for cutting.
Do not let the wires touch where they cross in the groove.
Switch on the electric current, and after a few seconds, the glass will usually crack in a clean cut where the wire has looped the jar.
If the glass does not crack after 15 seconds, switch off the electric current, remove the nichrome wire loop and hold the jar under running water.
The contraction due to cooling will break the jar along the desired line.
Be careful! Use caution during the actual breaking operation.
2.5.1 Clean microscope slides and coverslips
1. Soak microscope slides in one of the following solutions for 24 hours:
1.1 Chromic acid
1.2 Concentrated sulfuric acid or concentrated nitric acid
1.3 Equal parts of xylene and methylated spirit
1.4 Detergent in water
Then wash in running tap water.
Rinse twice in distilled water.
Store in acid alcohol.
2. Rinse in water.
Rinse in 95% alcohol.
Wipe the slides dry with a dry, clean, lint-free cloth.
3. Coverslips are more fragile than microscope slides.
Wash coverslips in detergent in water and rinse very carefully.
Store coverslips in acid alcohol or in 70% alcohol and dry as needed.
Discard coverslips used for smears or squashes and do not use them again.
Be careful! Do not leave whole or broken coverslips on the bench, because they can be picked up by a finger nail to scratch the eye.
4. Products:
Lens Cleaner Wipes, Clearwipe, lifts grease, dust and lint without scratching lenses, infused with solution that dries instantly leaving no streaks, can be used on microscopes, 20 wipes per box.
2.5.2 Cut sections by hand
See diagram 2.28: Cut sections by hand.
1. Cut a transverse section, (T. S.), at right angles to the long axis of the organ or plant.
Cut a longitudinal section, (L S), parallel to the axis of the organ or plant.
Cut a radial longitudinal section, (RLS), as with a longitudinal section, but cut along the radius of the organ or plant.
2. Make a transverse section, (T.S.), by cutting a carrot or piece of pith in half longitudinally.
Then hold the tissue to be sectioned between the two halves of the carrot or pith and cut across, away from you, with a one-sided razor blade, e.g. "Gem".
2.5.3 Microscopes and microscope accessories
Examples of microscopes suitable for schools follow in order of cost.
1. Stereoscopic microscope, 10X wide field eyepiece, 2X and 4X objectives, 240 V input, 12 V and 10 W incident and transmitted illumination
2. Monocular tube microscope, external illumination, magnification 40X, 100X and 400X
3. Monocular tube microscope, built-in illumination source, magnification 40X, 100X and 400X
4. Binocular head microscope, inclined 45o and 36o rotating, wide field eyepieces (WF10X/18 mm), quadruple nosepiece, plan objective (PL4X)
Achromatic objectives A (10X, 40X S, 100X), S-oil coaxial coarse and fine focussing adjustment, built-in low position coaxial mechanical stage
Rack and pinion focusable (1.25 N. A. Abbe condenser), iris diaphragm with filter holder, halogen illumination (12V / 20 W with intensity control)
Mains supply 220V-240 V (CE).
5. As above, but with triocular head, inclined 45o and 36o rotating.
Microscope accessories:
Cover glass, 18 mm × 18 mm / box
Cover glass, 22 mm × 22 m / box
Lamp, IEC lamp / self-contained / 240 V, 25 W
Lamp bulbs, 2140 V, 25 W, bayonet-type
Slides, clear glass, ground edges, plain / interleaved / pack
Slides, clear glass, ground edges, single concave cavity / pack.
Wipes, "Science wipes" (4103), for optical and delicate cleaning, 120 mm × 120 mm / box
Wipes, Lens cleaner wipes, "Clearwipe", individual sachet, 20 wipes per box
"Microscope set 36PC, with variety of tools and with blank and prepared slides
"Digital microscope, with up to 5 different magnification powers, you can display the microscope image on your PC and then capture, record, print and store images or videos.".
2.5.4 Microscopes and sunlight
Do not use direct sunlight to illuminate a microscope.
Use a low watt lamp bulb, e.g. 25 watts or 40 watts.
The bulb should also be pearl, not clear.
Direct sunlight reflected in microscope mirrors can cause eye damage to the eye.
If you must use sunlight, set up the microscope in a bright position near the windows, but not in direct sunlight.
2.5.5 Microscopes in the tropics
In tropical conditions, keep microscopes eye pieces and objectives in a desiccator that contains dry silica gel to absorb water.
Some brands of silica gel, e.g. "Tell Tale", change colour when they have absorbed much water.
This is a warning that it is time to heat the silica gel in an oven to expel the absorbed water.
Fungus may grow in the cement that holds the lens in the eyepiece or objective.
If any fungus is on a lens, take the eye piece or objective to an optical equipment shop for cleaning.
A piece of string soaked in creosote and placed in the lens container with the eyepiece may retard the growth of mould.
During the rainy season, store microscopes and sensitive electrical instruments in an airtight cupboard in which a 50 watt electric bulb is kept burning.
Rub petroleum jelly in a piece of cloth and keep needles inserted in it.
Grease metal instruments, e.g. screw gauges, vernier calipers and tuning forks and put oil on all screws.
Inspect regularly all metal items to check for damage by corrosion.
2.5.6 Parts of a microscope
See diagram 2.25: Parts of a microscope.
A microscope has a heavy base to ensure stability (5).
A curved frame, the limb, sits on the base and at its other end carries the tube support (6).
The stage (9), is a flat surface that projects from the frame, on which the specimens are placed.
At the centre of the stage is an opening for light to pass through.
Two specimen clamps on the stage are for clamping microscope slides in position (3).
The eyepiece lens, ocular (1), is at the upper end of the draw tube, (2), seated on the body tube support (6).
The draw tube is movable, so it can be extended to the correct setting for the lens.
The objectives (8), are screwed into the revolving nosepiece (7).
The shorter objective contains lenses for low power magnification.
The longer objectives contain lenses for high power magnification.
The nosepiece can be revolved to swing the selected objective into the light path.
A coarse adjustment knob and a fine adjustment knob (4), alter the distance between the specimen on the stage and the objective to focus the image.
Below the stage an iris diaphragm (10), is used to control how much light passes through the specimen.
In more complicated microscopes, not in the diagram, a condenser lens system under the stage can be raised or lowered to focus light on the specimen.
Under the iris diaphragm is a round mirror (11).
It is plane on one side and curved on the other side.
It is used to direct the light path and can be turned in any direction.
2.5.7 Prepare fresh material for microscope work
See diagram 2.27.1: Wet mount.
1. Examine fresh specimens in a drop of water.
Cover the water drop with a coverslip so that no water spills out on the slide and no bubbles of air remain under the coverslip.
Put on the coverslip by resting it with one edge against the water drop and then letting it fall slowly on the object.
This method reduces the chance of enclosing air bubbles.
2. Prepare direct microscopic mounts or squash preparations
Using sterile technique, remove a small portion of the colony with an inoculation needle.
Mount in a drop of Lactophenol Cotton Blue on a clean microscope slide.
Cover with a coverslip, squash the preparation with the butt of the inoculation needle and then blot off the excess solution.
2.5.8 Stain onion epidermis
See diagram 2.30: Detach epidermis from leaf.
Methyl green: 21
Aceto-carmine: 3.3.0
Methyl green acetic acid solution and carmine acetic acid (aceto-carmine) solution, simultaneously to fix and stain.
Transfer a drop of methyl green acetic acid to a slide with a glass rod.
Detach a small piece of epidermis from the inner side of a scale of an onion.
Put it immediately into the drop of methyl green acetic acid.
Apply a coverslip and examine the preparation at a magnification of 250 X.
The cell nuclei will be stained a strong blue-green colour, while the cell walls will only be weakly tinted.
The rest of the cell contents remain unstained.
The image in the microscope will be even more contrasting if, after the desired intensity of staining has been reached, the dye solution is replaced by 2% acetic acid.
Apply a drop of 2% acetic acid to one edge of the cover glass with a glass rod, and suck it under the cover glass by applying a piece of filter paper to the opposite side.
If carmine acetic acid is used, the cell nuclei are stained a deep red.
Use methyl green acetic for more fragile plant specimens and for showing the nuclei of protozoa.
2.5.9 Use of a microscope
See diagram 2.26: Drawing stain across specimen under coverslip.
1. Carry the microscope upright with two hands.
Place it gently on the table, not near the edge.
Do not slide it across the table.
Position the microscope so that looking into the eyepiece when seated is easy.
Always sit when using a microscope.
Clean all lenses with lens paper, not paper towel.
2. Switch on the microscope lamp.
Rotate the nose piece so no objective is over the stage opening.
Place the slide within the clips and position the specimen over the centre of the opening using the stage adjustment knobs or your fingers.
Begin each microscopic examination with a low power objective.
Rotate the low power objective until it clicks into place over the slide.
3. Look down into the eyepiece and adjust the round mirror below the stage so that the circular area seen through the eyepiece, the field of view, is brightly and evenly illuminated.
Look at the microscope from the side and use the coarse adjustment to move the stage upwards, or the tube downwards, until the distance between objective and specimen is 1 mm.
Never focus downward with the coarse focus unless looking from the side.
The objective must not touch the coverslip or the specimen.
Look down the low power eyepiece and use the fine focus knob to obtain a sharper focus.
4. Regulate the light intensity with the iris diaphragm.
While watching from the side, turn the nosepiece until the high power objective clicks into place.
It must not touch the slide.
Look into the eyepiece and use the fine adjustment knob to focus on the specimen.
An indistinct image of the object is formed with the high power objective so adjust the stage or the tube to refocus and sharpen the image.
Adjust the brightness of the image with the iris diaphragm under the stage.
Never use the coarse focus when using high power.
5. Return to low power and remove the slide after moving the objective up and away from the slide with the coarse focus knob.
2.6.1 Soldering
Soldering is used to join metallic surfaces such as copper, iron, nickel, lead, tin, zinc and aluminium for making electrical connections, joining sheet metal, sealing seams against leakage.
Electric soldering irons or guns are widely used for electrical connections, but soldering may also be done with coppers that do not have an electrical heating element.
Maintain the soldering iron at the appropriate temperature, because excessive heat can produce excessive lead vapour.
Ensure adequate ventilation with a small electric fan.
2.6.2 Solders
Solder, soft Pb and Sn alloys, resin-cored solder, wire form (Soldering flux, soldering resin).
Most soft solders are alloys of tin and lead.
Solders used for joining aluminium are usually alloys of tin and zinc.
Alloys of tin and cadmium are not used much nowadays, because cadmium is too dangerous.
The melting points of most tin lead solders range from about 165oC upwards.
Tin-lead solders have two numbers stamped on them to show percentage tin, then percentage lead.
Solders with a high tin content are used for electrical joints.
Solders with high lead content are used for greater mechanical strength.
Solders with a high tin content are more expensive than solders containing much lead.
Solders that contain a high percentage of tin usually have lower melting points than solders that contain a high percentage of lead.
Solders are available in various forms, including bars, wires, ingots and powders.
Wire solder is available with or without a flux core.
Products:
Solders sticks, 250 g, 50% tin / 50% lead
Solders, Consolidated alloys, 60% tin / 40% lead, roll
Weller electric soldering iron, 240 V, 40 W, pencil grip, 400oC tip temperature, 5 mm tip.
2.6.3 Flux
A flux is a substance added to lower the melting temperature in metallurgy and soldering.
The fusion of metals to form alloys is often done under a flux that may promote liquefaction, prevent volatilization and unnecessary exposure to the air.
1. The metal to be joined, the tip of the soldering iron and the solder must be clean.
Fluxes are used to clean the joint area, to remove the oxide film that is normally present on metal, and to prevent further oxidation.
Fluxes also decrease the surface tension of the solder and thus make the solder a better wetting agent.
Use a flux that is suitable for the metal to be joined, as shown below.
To make a good joint, the metal to be joined, the tip of the soldering iron and the solder itself must be freed of dirt, grease, oxides and other foreign matter that would prevent the solder from adhering to the metal.
2. Fluxes are generally classified as corrosive, mildly corrosive and non-corrosive.
The non-corrosive fluxes are used for soldering electrical connections and for other work that must be completely protected from any trace of corrosive residue.
Rosin is the most commonly used non-corrosive flux.
In the solid state, rosin is inactive and non-corrosive.
When rosin is heated, it becomes sufficiently active to reduce the oxides on the hot metal and thus do the fluxing action.
Rosin may be obtained as powder, paste, or liquid.
Use rosin for soldering brass, copper, tin and lead.
Use zinc chloride for soldering galvanized iron, and zinc.
Use borax (hydrated sodium borate) or sal ammoniac (ammonium chloride) for soldering iron and steel.
Use a special flux for soldering aluminium.
3. Rosin fluxes often leave a brown stain on the soldered metal.
This stain is difficult to remove, but it can be prevented to some extent by adding a small amount of turpentine to the rosin.
Glycerine is sometimes added to the rosin to make the flux more effective.
Rosin is a solid amber residue made by the distillation of turpentine from pine stumps.
4. Lead fluxes may lead to kidney damage.
Do not use fluxes containing fluoride.
2.6.4 Methods of soldering
1. All surfaces to be soldered must be clean and free of oxide, dirt, grease or other foreign matter.
The materials to be soldered should be joined mechanically, so the solder fixes the joint in place, just like carpenter's glue holds a woodworking joint.
2. Use a solder and flux that are appropriate for the particular job.
The melting point of the flux must be below the melting point of the particular type of solder you are going to use.
3. Heat the surfaces just enough to melt the solder.
Solder will not stick to unheated surfaces.
Do not heat the solder ed much above the working temperature, because as the temperature of molten solder increases, the rate of oxidation is increases.
When molten solder is overheated in air, more tin than lead is lost by oxidation.
2.6.5 Soldering electrical connections
See diagram 2.32: Soldering electrical connections.
Use the rosin core solder, because washing off acid flux from electrical gear is difficult.
Any acid that remains from the soldering operation causes corrosion.
To solder electrical connections, hold the soldering iron, the copper, beneath the splice being soldered, with the greatest possible area of mechanical contact to permit maximum heat transfer.
Apply the rosin core solder to the splice.
Be careful! Do not to overheat electrical components.
2.6.6 Torch soldering
Torch soldering is often used for small jobs or for work that is relatively hard to reach.
A propane torch or an alcohol torch may be used.
The general procedure is to play the flame from the torch on to the surfaces to be joined and then apply cold solder in bar or wire form.
The heated surfaces will melt the solder.
As the solder melts, wipe off any excess solder with a damp cloth, before the solder hardens.
2.7.0 Tools for electrical experiments.
Electrical equipment Commercial
Cable knife
Circular level, 35 mm
Coil of soldering wire, 2 mm
Combination pliers, 185 mm, chrome plated, insulated
Combination pliers, length 160 mm
Hammer (engineer hammer) 200 g
Pincers, length 230 mm
Plumb bob metal, cord length 1000 mm
Rosin soldering wire, d = 1 mm
Scissors, 180 mm, universal (e.g. for metal sheet) black
Screw holder, 140 × 6 mm
Screwdriver, 125 mm × 7 mm, for slotted screws, plastic handle
Screwdriver, width 3 mm, with plastic handle
Screwdriver, 100 mm × 4 mm, for slotted screws, plastic handle
Screwdriver, size 2, for phillips screws, plastic handle
Side cutting pliers, 145 mm, chrome plated, insulated
Soldering iron, 220 v, 50 w
Spanner, 8 mm, plastic handle
Spirit level, length 200 mm
T-handle socket spanner, 5.5 mm, plastic handle
Telephone pliers, 165 mm, chrome plated, insulated
Voltage tester, screw-driver with discharge lamp, for voltages between 135 to 240 v
Watchmaker screwdriver, set of 6 Wire stripper, 165 mm, chrome plated, insulated
2.8.0 Equipment for electrical experiments
8.1 Balls
8.2 Metallic sheets, plates, foils
8.3 Threads and cords
Wire
8.4 Wire diameters, SWG
8.5 Wires, nails and rods
8.1 Balls
Steel balls
Bearing balls, hardened and polished, 25 mm, 19 mm, 13 mm, 2 mm
Lead shot 3 mm
8.2 Metallic sheets, plates, foils
Aluminium foil | Aluminium plate | Aluminium sheet | Copper sheet | Lead sheet, for analyses | Silver sheet | Steel plate | Steel sheet | Tin foil | Zinc sheet
8.3 Threads and cords
Silk thread, sewing silk
Nylon thread, 0.4 mm
Fishing line, diameter 0.7 mm, 0.5 mm
Cotton cord 2.5 mm
PVC cord 3 mm
8.4 Wire diameter, SWG
Diameters of wires are measured in terms of Standard Wire Gauge, SWG (UK, Australia) or Brown and Sharpe (B & S) (American Wire Gauge)
SWG 50 is the smallest gauge
Cable sizes are shown as follows:
14/36 = 14 strands of 36 SWG wire to carry 2 amps for internal lighting in a motor car, or 61/20 = 61 strands of 20 SWG wires to carry
150 amps suitable for 6 volt starter motors in a car'.
Wire Gauge Conversion
AWG = American Wire Gauge, inches as decimals of an inch, excluding the metric numbers
AWG = American Wire Gauge, Metric wire gauge is 10 times the diameter in millimetres and shown as "MM" B and S = Brown and Sharpe, inches.
SWG = Imperial Standard Wire Gauge (British legal standard) inches
Table 8.4.
SWG. Wire No. AWG.
or BandS		 AWG.
metric
Inches Gauge Inches m.m.
0.300 1 0.289 297 7 348
0.276 2 0.257 627 6 543
0.252 3 0.229 423 5 827
0.232 4 0.2 043 5 189
0.2 120 5 0.1 819 4 621
0.1 920 6 0.1 620 4 115
0.1 760 7 0.1 443 3 665
0.1 600 8 0.1 285 3 264
0.1 440 9 0.1 144 2 906
0.1 280 10 0.1 019 2 588
0.1 160 11 0.0 907 2 304
0.1 040 12 0.0 808 2 052
0.0 920 13 0.0 720 1 829
0.0 800 14 0.0 641 1 628
0.0 720 15 0.0 571 1 450
0.0 640 16 0.0 508 1 291
0.0 010 50 0.0 010 0.0 254
8.5 Wires, nails and rods
Chrome-nickel wire 0.1 mm
22.7.6.6 Constantan wire 15.6 ohm / m, 6.9 ohm / m, 0.98 ohm / m
Copper wire 0.2 mm, 0.4 mm, 0.5 mm
Copper wire, insulated 0.6 mm
Copper wire, lacquered 0.6 mm
Hooks, s-shape
Iron wires, pack of 20
Iron wire 0.2 mm, 0.5 mm, 1.0 mm
Iron nails, pack of 25 1.6 mm, length 35 mm
Iron rods, flexible, 2.0 mm
Iron wire, notched diameter 1.2 mm, copper plated
Kanthal wire 19.1 ohm / m 0.3 mm
Knitting needles 2.0 mm
Metal rods, Cu, Al, Fe
Nickel wire 0.3 mm
Platinum wire on glass rod 0.15 mm
Platinum wire 0.15 mm, 0.3 mm
Silver wire 0.5 mm
Spring steel wires, pack of 20
Suspension wire 30 n (tungsten wire) 0.1 mm
Wire 27.9 ohm / m 0.25 mm
Wood splints, pack of 100
2.1.0 Charcoal, Activated charcoal
Activated carbon (industrial information)
(Non-SI unit "micron" = 1 micrometre)
Wood charcoal is formed by destructive distillation of wood.
Charcoals are used to purify gases and liquids, e.g. coconut shell charcoal.
Animal charcoal is made from bones and is used for sugar refining.
If more than 4000 mg per day taken as dietary supplement may cause stomach upset, diarrhoea, constipation or vomiting, blackened teeth and painful stools.
Industrial website information:
1. Activated carbon water filters are fast acting and very effective in removing unpleasant taste and odours from water.
They are made from coal, coconut, lignite and wood.
These materials are heated to extreme temperatures in the absence of oxygen, leaving millions of microscopic pores for contaminants to be absorbed.
There are three main types of carbon filters: Paper wound, Granular (GAC) Carbon Block.
The effectiveness of a carbon filter depends on the carbon used, the design and how slowly water is passed through the filter.
Cartridges are usually micron-rated and have different sediment holding capabilities.
As cartridges go from coarser to finer in their filtration rating, they become less efficient in sediment holding.
On fine or sub micron carbon filters a 5 to 3 micron sediment filter should be fitted before the carbon filter to prevent plugging.
2. Cartridge examples:
A: Matrix CTO 10 um
A high quality carbon block filter with good sediment retention and chlorine removal ability.
B: Matrix Pb1 1 um
A high quality carbon block filter with iron exchange media to reduce dissolved lead and other heavy metals.
Effective on water that has Giardia and Cryptosporidium present.
C: GAC 10 um.
A granular activated carbon filter
Offers good chlorine reduction with a good flow rate.
3. Activated carbon is also called activated charcoal and decolorizing carbon.
It is made by heating charcoal to about 930oC, where it gains a large surface area to maximize reactions with unwanted substances.
Activated carbon can be coal-based, coconut-based and lignite-based.
The activated carbon works by adsorption, i.e. substances are attached to the surface of the carbon, not absorption where substances mix with the absorbing material, e.g. a beach towel.
It can be used to absorb unburnt gases from exhausts of motor cars, colours from products and harmful gases in the air, bad tasting chemicals from water.
Experiment
Put activated carbon in a filter paper in a filter funnel.
Add a few drops of difference substances to 100 mL of water and pour the solution onto the activated carbon.
Compare the colour of the original solution and the filtered solution.
The substance to be tested can include food colourings, pickle juice, vinegar, potassium permanganate (VII) crystals.