UNPh06

School Science Lessons
Equipment
2009-10-10
Please send comments to: J.Elfick@uq.edu.au

Table of contents
1.3.0 Weighing devices, balances (Primary)
1.12.0 Low-cost equipment
1.28.0 Simple equipment, construction
2.1.0 Equipment, care, radiation, lasers
2.15.0 Glass, cutting, tubing, cleaning
2.22.0 Microscopes, care, use, staining techniques
2.31.0 Soldering, solders, fluxes, methods
6.5.0 Teaching facilities
3.3.0 Equipment safety
8.0 Electrical experiments equipment

1.3.0 Weighing devices, balances (Primary)
2.16 Compare our weights
2.23 See-saw balance
2.24 Steelyard balance
2.25 Make a ruler balance
2.26 Balance bottle tops
2.27 Nail balance
2.28 Beam balance
2.29 Microbalance, drinking straw balance
3.19 Single pan balance / simple balance
4.21 Measure our weight

1.12.0 Low-cost equipment
1.31 Metal can heater
1.32 Make distilled water
1.33 Air oven
1.34 Test-tube holder
1.35 Laboratory tweezers (forceps)
22.1 Measuring devices, calorimeter, measuring cylinder
22.2 Heat sources
28.11.0 Optical devices

1.28.0 Simple equipment, construction
1.28 Simple calorimeter
1.29 Measuring cylinder / graduated cylinder
1.31 Metal can heater
1.32 Making distilled water
1.33 Air oven
1.34 Test-tube holder
1.35 Laboratory tweezers (forceps)

2.1.0 Equipment, care, radiation. lasers
2.1 Gas installations and inspections
2.2 Electrical outlets and equipment
2.3 Blueprints and diazo prints
2.4 Fume cupboards
2.5 Water stills
2.6 Prepare stock materials and apparatus
2.7 Prepare sets of apparatus for the following purposes
2.8 Unpack, check and sort new equipment
2.9 Stock control
2.10 Razor blades and knives
2.11 Gas-Pak
2.12 Radiation hazards
2.13 Lasers and laser hazards
2.14 Filtering

2.15.0 Glass, cutting, tubing, cleaning
2.15 Cut window glass and Perspex with a straight cut
2.16 Cut glass tubing
2.17 Bend glass tubing
2.18 Insert glass tubing through a stopper
2.19 Remove glass tubing from a stopper
2.20 Glass cleaning
2.21 Resistance wire glass jar cutter

2.22.0 Microscopes, care, use, staining techniques
2.22 Microscopes in the tropics
2.23 Clean microscope slides and coverslips
2.24 Microscopes and sunlight
2.25 Parts of a microscope
2.26 Use of a microscope
2.27 Prepare fresh material for microscope work
2.28 Cut sections cut by hand
2.29 Stain living specimens, Daphnia.
2.30 Stain onion epidermis

2.31.0 Soldering, solders, fluxes, methods
2.31 Soldering
2.32 Solders
2.33 Fluxes
2.34 Methods of soldering
2.35 Electrical connections
2.36 Torch soldering
38.2.02 Soldering for electronic circuits

1.31 Metal can heater
See diagram 22.1.3
A heater can be made from an old oil tin. Water is placed in the tin and heated from below. Iron wire is wrapped round a test-tube and twisted to form a handle. The substance to be heated is placed in the test-tube

1.32 Make distilled water
See diagram 1.32
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.

1.33 Air oven
See diagram 1.33
A large metal can be used as an air oven. A hole through the lid fitted with a cork holds a thermometer, and the saucer or dish rests on a wire gauze bridge placed inside the tin.

1.34 Test-tube holder
Make a test-tube holder by bending into shape strong spring wire, e.g. wire from a coat hanger.

1.35 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.

2.1 Gas installations and inspections
1. Portable 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, whether involved in a practical activity or not, 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 Electrical outlets and equipment
1.0 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.
2.0 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. 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.

3.0 Use safe practice and procedures
3.1 Dry hands thoroughly before operating any switch.
3.2 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. Also, do not attempt to repair mains-operated equipment, e.g. hot water systems, ceiling fans, refrigerators.
3.3 Switches must be in the "off" position before inserting plugs or removing plugs from power points.
3.4 When removing plugs from power points, grasp the plug firmly and pull. Do not pull on the lead.
3.5 Do not let students push metal objects into power points or poke at pilot lights with metal objects.
3.6 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.
3.7 Avoid using 240 volt equipment near sinks or water outlets or close to gas outlets where accidental sparking may ignite gas leaks.
3.8 Disconnect portable appliances from the power outlet when not in use or before cleaning.
3.9 When connecting several appliances to the mains, use power boards not double adapters.
3.10 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.
4.0 Management of electric shock victims
4.1 Turn off the electricity supply OR disconnect the victim from the electricity supply by using of a dry non-conducting material, e.g. dry clothing, a wooden stick. Before disconnection, avoid any direct contact with the skin of the victim or any conducting material touching the victim.
4.2 Commence cardiopulmonary resuscitation if the patient's heart has stopped beating.
4.3 Seek medical help.

2.3 Blueprints and diazo prints
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.
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.

2.4 Fume cupboards
1. 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.
2. Types of fume cupboards with different methods of dispersal to the atmosphere
2.1 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.
2.2 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.
2.3 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.

2.5 Water stills
A potential hazard 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.

2.6 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, candles, cardboard squares, clothes-pegs, copper wire, copper sheet, copper turnings, corks, cork slabs, hand drill, dry cells, torches, fibreglass, plastic, bronze mesh, fly screens, flannel rags, table forks, G-clamp, drinking glass, hacksaw blades, iron filings, iron nails, iron sewing needles, fencing wire, plastic lenses, marbles, mirrors, olive oil, ping-pong balls, pith, plastic rulers, razor blades, rubber balloons, rubber bands, rubber suction cups, silk pieces, thread, springs, thermometers, wood screws, screw eyes, jam tins with press-on lids, plastic containers, tin snips, cotton reels, metal pulley wheels, brass and iron pins, assorted hand tools, cardboard cylinders, chalk boxes, grease-proof paper, paste, Plasticine (modelling clay, plastilina).

2.7 Prepare sets of apparatus for the following purposes:
1. Consistent use in daily laboratory activities, e.g. glassware sets
2. Occasional use in demonstrations, or in rotation by student groups
3. Individual pupil 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.

2.8 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 breakages 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.

2.9 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 stock take 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 breakages as soon as practicable after they occur. This is essential if you are to account for all apparatus at the next stock take.
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 stock take all equipment should be inspected by the stock taker 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.

2.10 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 normal 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.

2.11 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 and turn 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.

2.12 Radiation hazards
1. Radioactive substances usually emit alpha particles or beta particles or gamma rays or combinations of these. X-ray units generate electromagnetic waves similar to gamma rays, but usually of lower frequency and longer wavelength. The amount and type of shielding needed depend on the penetrating power of the particular form of radiation. Sources of radiation are limited to sealed sources, radioactive chemical and mineral samples and high voltage electrical equipment.
Alpha particles are charged and relatively heavy atomic particles so are easily stopped by a sheet of paper or the surface of the skin.
Beta particles are stopped by a few millimetres thickness of aluminium or 2 cm of plastic material.
Gamma rays have very short wavelength and are more penetrating and harder to stop. They are almost completely stopped by about 1 metre of concrete or about 5 cm of lead. Most will pass through the human body.
Medical X-rays are almost completely stopped by 3 millimetres of lead or 15 centimetres of concrete. X-rays pass through the body with some absorption depending on the density of organs, e.g. skin, bones.
2. Ionizing radiation in schools must only be used in simple experiments to demonstrate fundamental principles. The sources used and the methods of using them must be chosen to ensure that the degree of hazard is negligible. In school experiments involving X-rays or radioactive substances the radiation levels should be so low that no special shielding is required. However, it is important when using sources of radiation in schools to demonstrate the role of shielding as part of safe working practices. All radiation sources must be stored in separate lockable metal containers, e.g. a metal cash box, which are permanently labelled and kept in the school safe with access to authorized members of the school staff.
3. Cold cathode discharge tubes may include a discharge tube with side tube for connection to a vacuum pump, Maltese cross discharge tube, discharge tube to illustrate the deflection of cathode rays by magnetic fields, windmill tube. These tubes are operated by high voltages produced by induction coils and may produce unwanted X-rays if operated at too high a voltage. Use the lowest possible voltage from the induction coil changing the distance of the make-and-break hammer from the iron core of the induction coil windings. Commence with the hammer well away from the core and use the adjusting screw to slowly decrease the distance between them until the discharge tube operates. Only teachers should operate a discharge tube, for a short a time as possible and with both teacher and student at a minimum distance of one metre from it.

2.13 Lasers and laser hazards
1. Lasers can burn tissue in the eye because the lens of the eye may concentrate the laser beam to a very small image on the retina. High power lasers may damage the skin. Lasers are classified according to the degree of hazard that depends on the output power, the size of the beam, the irradiance at any point in the beam, the wavelength, and the power in a single pulse and the repetition frequency if it is a pulsed laser. All lasers and laser products must bear a label stating the class of the laser product, the wavelength emitted or the medium, and maximum power output.
2. Class 1 lasers cannot cause harm because the exposure level that produces injury cannot be reached under any conditions. Class 2 lasers are low power devices that emit visible radiation. Blinking should protect the eyes from them. Classes 3A, 3B and 4 lasers are not permitted in schools.
3. The teacher should warn students that they should never shine a laser beam directly into a person's eyes. Some irresponsible people have direct laser beams at the drivers of moving vehicles and the pilots landing aeroplanes.
4. Sunglasses and welder's goggles do not provide protection from laser beams. Use approved shields to prevent both strong reflections and the direct beam from going beyond the area needed for the experiment. Paint the shields matt black to reduce reflection. Reflection of laser beams may occur from polished metal trimmings on instrument housings and from mirrors, bottles, glass lenses, watches, rings, cufflinks, polished wooden furniture, windows or any smooth surface. Fix the laser head rigidly in position so that the direction of the laser beam cannot be accidentally altered. The room lighting in the laser work area should be as bright as possible to constrict the pupil diameter of the observer's eyes.

2.14 Filtering
See diagram 2.14: Folding filter paper

2.15 Cut window glass and Perspex with a straight cut
See diagram 2.15: Straight cut
1. 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. 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. Cut 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 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 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 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, which consists of two or more glass sheets cemented together by a transparent plastic, requires special cutting equipment.

2.16 Cut glass tubing
See diagram 2.16: Break and bend glass tubing
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. Another method frequently used is to scratch the glass tubing with a quick smooth file stroke, then hold the scratched tubing firmly in both hands with one's thumbs pointing towards each other, but on opposite sides of the scratch, and snapping the glass tubing away from one's body. Fire polish the cut ends.
2. 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.
3. 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.
4. 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.
5. 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 becomes thin into capillary. If go on pulling, the thinnest part will fall down thus 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.
6. Seal the end of a thick glass tube
Place one end of 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. 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.

2.17 Bend glass tubing
See diagram 2.16
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.

2.18 Insert glass tubing through a 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. Then use the next larger size borer and push this over the cork borer already in the stopper from the other side. Then 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 which will be inserted since the cork is poor in 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.

2.19 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.

2.20 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.
1. 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. 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.
3. Cleaning agents, "chromic acid".
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!
4. 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: 1. ethanol (ethyl alcohol) 2. propanone (acetone) 3. trichloromethane (chloroform) 4. xylene, do not pour into the sink, keep and discard with wastes 5. hexane, do not pour into the sink, keep and discard with wastes 6. petroleum ether, do not pour into the sink, keep and discard with wastes.
5. Dry glassware after cleaning
Air dry glassware on racks. Rinse in ethanol (100%), propanone or ether and blow air through the vessel. Dry beakers, pipettes, and flasks in an oven at 110^oC, after rinsing in water BE CAREFUL! Ethanol, propanone and ether are highly flammable. All burners and gas heaters should be extinguished before using them!
6. 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 obviously 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.

2.21 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.

2.22 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 callipers and tuning forks and put oil on all screws. Inspect regularly all metal items to check for damage by corrosion.

2.23 Clean microscope slides and coverslips
1. Soak microscope slides in one of the following solutions for 24 hours: 1. chromic acid 2. concentrated sulfuric acid or concentrated nitric acid 3. equal parts of xylene and methylated spirit 4. detergent in water. Wash in running tap water. Rinse twice in deionized 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 under a finger nail to scratch the eye.

2.24 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.

2.25 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.

2.26 Use of a microscope
See diagram 2.26: Microscope technique
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. 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. 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. 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. Return to low power and remove the slide after moving the objective up and away from the slide with the coarse focus knob.

2.27 Prepare fresh material for microscope work
See diagram 2.27: Wet mount
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.

2.28 Cut sections cut by hand
See diagram 2.28: Cut sections cut 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, R. L. S., as with a longitudinal section but cut along the radius of the organ or plant.
2. Make a transverse section 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".

2.29 Stain living specimens, Daphnia
See diagram 9.37: Daphnia
A few dyestuffs, which are only slightly poisonous, may be used in very dilute aqueous solution for staining living specimens for microscopic examination, e.g. neutral red and cresyl violet.
1. Put some Daphnia into a beaker containing 0.1% neutral red solution. After 10 minutes, transfer them into a drop of the dye solution on a microscope slide and examine at 60 X. The individual organs and parts of the body are coloured red.
2. Add 6 drops of a saturated aqueous cresyl violet solution to 30 mL deionized water. Put a drop of this solution on a microscope slide and add a drop containing Daphnia. Cover with a coverslip and examine at 60 X. After a few minutes, the gill sacs appear blue, the tactile hairs of the first pair of antennas red, the stomach and the heart yellow and the eggs green.

2.30 Stain onion epidermis
See diagram 2.30: Detach epidermis from leaf
Methyl green acetic acid solution and carmine acetic acid solution simultaneously 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.

2.31 Soldering
Soldering is used to join metallic surfaces such as copper, iron, nickel, lead, tin, zinc and aluminium. It is particularly useful for making electrical connections, joining sheet metal and sealing seams against leakage. 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.

2.32 Solders
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 165^oC 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.

2.33 Fluxes
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.

2.34 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.

2.35 Electrical connections
See diagram 2.32: Solder electrical connection
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.

2.36 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.

6.5.0 Teaching facilities
Blackboard Tools
Audio
Slide Projectors
Film Projectors,
Overhead Projectors
Video and Computer Projection,
Photography
XY Chart Recorders
Museums,
Resource Books
Films
Computer Programs
Mechanical: Motor
Pumps
Vacuum
Air Support
Ripple Tank