School Science Lessons
6. Equipment, activated carbon, electrical, glass cutting, microscopes,
soldering, weighing devices
2012-05-05 SPwP
Please send comments to: J.Elfick@uq.edu.au
Table of contents
6.0.0 Equipment
6.1.0 Biology equipment and solutions
8.0.0 Electrical experiments equipment
6.2.0 Equipment and solutions
2.1.0 Equipment care
2.0.0 Glass cutting, tubing, cleaning
22.8.0 Laboratory equipment
1.12.0 Low-cost equipment, simple equipment
2.22.0 Microscopes, care, use, staining techniques
2.31.0 Soldering, solders, fluxes
7.0.0 Tools for electrical experiments
6.1.0 Biology equipment and solutions
4.0 Biology fixatives
1.0 Biology media and solutions
6.0 Culture media for routine cultivation
and identification of fungi
9.9.18 Hydroponics, soil-less culture solutions
4.7 Insect fixing fluids
6.2.0 Equipment and solutions
4.0 Chemistry, chemicals
8.0.0 Electrical experiments equipment
7.0.0 Electrical experiments, Tools for electrical experiments
Part 16.2 Equipment and software (commercial websites)
Part 16 Equipment, chemical suppliers (commercial)
3.3.0 Equipment safety
3.0.0 Laboratory Safety
7.0.0 Laboratory safety for physics teaching
Safety equipment
SDS Queensland Education Supplies catalogue (Internet)
7.9.6.2 "Solution", aqueous solution
5.0 Solution, Standard buffer solutions
5.0.0 Solutions and mixtures
6.5.0 Teaching facilities
UNESCO List of equipment for science curriculum development
7.0 Weighing devices, balances (Primary)
2.1.0 Equipment care
2.3 Blueprints and diazo prints
See
pdf: Blueprint, Sun Blueprint Paper
2.2 Electrical outlets and equipment
2.14 Filtering
2.4 Fume cupboards
2.1 Gas installations and inspections
2.11 Gas-Pak
2.6 Prepare stock materials and apparatus
2.7 Prepare sets of apparatus for the following purposes
2.10 Razor blades and knives
2.9 Stock control
2.8 Unpack, check and sort new equipment
2.5 Water stills
2.0.0 Glass cutting, tubing,
cleaning
2.17 Bend glass tubing
2.16 Cut glass tubing
2.15 Cut window glass and Perspex, (Lucite), with
a straight cut
2.20 Glass cleaning
2.18 Insert glass tubing through a stopper
2.19 Remove glass tubing from a stopper
2.21 Resistance wire glass jar cutter
22.8.0 Laboratory equipment
1.6 Beakers
1.7 Bottles, laboratory bottles
1.24 Bottle brushes, stirring rods, watch glass
1.26 Burettes
1.23 Crucibles
1.30 Dissection kits
1.23 Evaporating basins
1.5 Filter funnels
1.27 Flasks, borosilicate glass flasks
1.22 Hazard labels
1.29 Measuring cylinders / graduated cylinder
1.23 Mortar and pestles
1.31 Petri dishes
1.25 Pipettes
1.23 Porcelain laboratory items
1.19 Retort stands
1.10 Screw compressors
1.11 Spatulas
1.23 Spotting tiles
1.8 Stoppers, rubber stoppers
1.9 Test tubes
1.4 Tongs
1.14 Tripod stands
1.12 Tubing
1.18 Wax tapers
1.13 Wire gauze mats
1.12.0 Low-cost equipment,
simple equipment
22.8.0 Heat sources
1.35 Laboratory tweezers (forceps)
1.29 Measuring cylinder / graduated cylinder
1.31 Metal can heater
28.11.0 Optical devices
1.32 Prepare distilled water
1.28 Simple calorimeter
1.34 Test-tube holder
2.22.0 Microscopes, care,
use, staining techniques
2.22.0 Microscopes and microscope accessories
2.23 Clean microscope slides and coverslips
2.28 Cut sections cut by hand
2.24 Microscopes and sunlight
2.22.01 Microscopes in the tropics
2.0 Microscopy adhesives
3.0 Microscopy stains
2.25 Parts of a microscope
2.27 Prepare fresh material for microscope work
2.29 Stain living specimens, Daphnia.
2.30 Stain onion epidermis
2.26 Use of a microscope
2.31.0 Soldering, solders,
fluxes
2.32 Solders
2.33 Fluxes
2.31 Soldering
2.35 Soldering, Electrical connections
38.2.02 Soldering for electronic circuits
2.34 Soldering, Methods of soldering
2.36 Soldering, Torch soldering
1.4 Tongs
Beaker tongs, stainless steel with rubber grips, suitable for 50 mL to
2000 mL beakers.
Crucible tongs, brass metal, 200 mm.
1.5 Filter funnels
Filter funnels, polyethylene, 75 mm.
Filter funnels, soda glass, 1000 mm.
1.6 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.
1.7 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.
1.8 Stoppers, rubber stoppers
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.
Rubber stoppers, two holes.
1.9 Test tubes
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 tubes, Pyrex with rim, 25 mm × 200 mm, box /50.
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 holders, plated spring steel wire, holds up to 30 mm test tube.
1.10 Screw compressor
Screw compressor, Hoffman type, 20 mm, opening with hinged bottom, nickel-plated
brass.
1.11 Spatulas
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.
1.12 Tubing
Plastic tubing, clear, 8 mm inside diameter, 30 metre roll.
Glass tubing, 6 mm outside diameter, 750 mm length.
1.13 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.
1.14 Tripod stand
Tripod stand, triangular, 200 mm high, 125 mm side.
1.15 Timers, digital timers
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.
1.16 Indicator papers
Indicator papers, pH 0 to 14, strips, universal, non-bleeding, pack /
100.
Indicator papers, pH 0 to 14, full range, 30 second development, 5 metre
reel.
Litmus paper, 20 sheets per booklet, pack / 10 booklets.
1.17 Chromatography paper
Chromatography paper, Bonnett, 1518 Grade 1CHR, 200 mm × 200 mm,
pack / 100.
1.19 Retort stand
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.
1.22 Hazard labels
Diamond shaped adhesive labels, 20 mm × 20 mm.
OXIDIZING AGENT, roll / 250.
FLAMMABLE, roll / 250.
TOXIC, roll / 250.
CORROSIVE, roll / 250.
1.23 Porcelain laboratory items
Crucibles with lid, 30 mL.
Mortar and pestle 10 mm.
Spotting tile, 12 depressions, 110 mm × 90 mm.
Evaporating basin, bowl shape, 75 mL.
1.24 Bottle brushes, stirring
rods, watch glass
Bottle brush, 17 mm diameter, 50 mm brush, 150 mm overall length.
Bottle brush, 25 mm diameter, 75 mm brush, 200 mm overall length.
Stirring rod, glass 6 mm outside diameter, 150 mm.
Stirring rod, glass 6 mm outside diameter, 300 mm.
Soda watch glass, ground edge, 125 mm diameter.
1.25 Pipettes
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.
Danger of using pipettes in the laboratory
Glass pipettes can cause lacerations to the hands of operators. Mouth
pipetting is prohibited so pipette aids, fillers and pumps can 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 pipetters 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, which inserts into the end of the pipette, and has no valves has
no recorded pipette breakage but this 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- or
battery-operated pump can be set up
to service several students.
1.26 Burettes
See diagram 1.26: Burette
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 holder.
1.27 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.
1.29 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. Next, obtain a commercial graduated cylinder of
about the same capacity as the bottle and 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.
Commercial 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.
1.30 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.
1.31 Petri dish
Clear plastic, 90 × 14 mm, pack / 20.
1.32 Prepare distilled water
See diagram 23.32
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.
1.34 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. 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.
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
See
pdf: Sun Blueprint Paper
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, fume hoods
See diagram 1.13a: Simple fume hood
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 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.
2.9 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 breakage 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 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.
2.14 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:
4.1 ethanol (ethyl alcohol),
4.2 propanone (acetone),
4.3 trichloromethane (chloroform),
4.4 xylene, do not pour into the sink,
keep and discard with wastes,
4.5 hexane, do not pour into the sink, keep
and discard with wastes,
4.6 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, 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 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.
2.22.0 Microscopes and microscope
accessories
Order online: Microscope: Make your
own
Examples of microscopes suitable for schools follows 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:
Commercial:
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.
Commercial:
"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."
2.22.01 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.
4. Commercial 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.
2.24 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
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.
2.27 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. Maintain the soldering iron
at the appropriate temperature because excessive heat can produce excessive
lead vapour. Ensure adequate ventilation with a small electric fan.
2.32 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.
Commercial:
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.
2.33 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.
4. Lead fluxes may lead to kidney damage. Do not use fluxes containing
fluoride.
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
7.0.0 Tools for electrical experiments
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
8.0.0 Electrical experiments
equipment
8.1 Balls
8.2 Metallic sheets, plates, foils
8.3 Threads and cords
8.4 Wire diameters, SWG
8.5 Wires, nails and rods
8.6 Prepare electrolyte for a lead accumulator cell
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"
BandS = Brown and Sharpe, inches
SWG = Imperial Standard Wire Gauge (British legal standard) inches
| 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
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
8.6 Prepare electrolyte for a
lead accumulator cell
Be careful! Use safety glasses and nitrile chemical-resistant gloves! Wear protective clothing. Follow
the recommendations of the manufacturers for filling and initial charging
that is usually printed on the battery. The relative density of sulfuric is fully charged 1.28, half charged,
1.21, discharged 1.15. Slowly add concentrated sulfuric acid, with stirring,
to a strong beaker two thirds full of deionized water or distilled water,
until the solution almost boils. Leave to cool and add more acid until the
solution almost boils.
Leave to cool to room temperature. Adjust the relative
density by adding more acid or more water, according to the hydrometer reading.
When the cell is not in use, use a jar with a cover to prevent drying by
evaporation.
11.0 Activated carbon
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.
Commercial information:
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.
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.
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
automobile
exhaust, colours from products and harmful gases in the air,
bad tasting chemicals from water. 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.
12.0 Science teaching support
systems and facilities
1. Blackboard Tools
2. Audio equipment
3. Slide Projectors
4. Film Projectors
5. Overhead Projectors
6. Video and Computer Projection
7. Photography equipment
8. X-Y, Chart Recorders
9. Computer Programs
10. Motors
11. Pumps
12. Vacuum equipment
13. Ripple Tank