School Science Lessons
Physics - Heat and temperature, thermometers, melting point
Updated: 2008-03-28 L
Please send comments to: J.Elfick@uq.edu.au
See also: Interesting websites
Table of contents
4.1.0 Heat as energy
4.5.0 Expansion
4.10.0 Latent heat
4.16.0 Conduction of heat
4.24.0 Convection
4.32.0 Radiation
4.37.0 Quantities of heat
22.0 Heat and temperature
22.1 Heat measuring devices, calorimeter
22.2 Heat sources, spirit burner, alcohol lamp (low cost)
22.4 Candle burner
22.6 Bunsen burner, "Gas-Pak"
22.7 Thermometry, thermometer, temperature
7.4.0 Melting point, m.p. of solids
7.5.0 Boiling point, b.p. of liquids
7.7.5 Solubility of different salts and temperature
22.0 Heat and temperature
7.0 International system of units (SI), the 7 base units
7.6 Temperature, the Fahrenheit scale and the Celsius scale
7.7 The Kelvin scale
7.8 The triple point
22.2.1 Heat has no weight
22.2.3 Heat absorbed depends on mass
22.2.4 Heat dissipation
22.2.5 Heat a solid sphere and a hollow sphere
2.8 Pressure affects the boiling point
12.1.3 Pressure on solid ice
3.24 Air temperature (Primary)
4.10 Heat different solids (Primary)
4.11 Temperatures during the day (Primary)
5.17 Body temperature (Primary)
22.1 Heat measuring devices, calorimeter
23.9.0.1 The units of work and energy, joule and calorie
4.38 Calorific value of fuel
1.28 Simple calorimeter
1.29 Measuring devices, measuring cylinder
22.2 Heat sources
22.1.1 Simple heater
22.1.2 Drink-can charcoal burner
22.1.3 Make an alcohol lamp, spirit lamp, from an ink bottle
2.20 Spirit burner (alcohol lamp) (primary)
22.4 Candle burner
8.1.2 Gaseous products of a burning candle
8.1.1 Candle flame
8.1.1.1 Candle flame parts
8.1.1.2 Candle flame and soot
8.1.1.3 Candle flame, dark region
8.1.1.4 Gases from the wick
8.1.1.5 Candle flame with aluminium foil held below it
8.1.2 Candle flame, gaseous products
2.44 Candle flame (Primary)
4.9 Burning candles over water
6.35 Burn candle over water (Primary)
22.6 Bunsen burner, "Gas-Pak"
3.1.0 Bunsen burner
8.1.4.1 Bunsen burner, flame
8.1.4.2 Bunsen burner, flame, which part is hottest
8.1.4.3 Bunsen burner, flame can melt copper wire
13.2.1 Bunsen burner, flowing air can do work, application of Bernoulli's law
Bunsen burner, "Gas-pak "" 2.11
22.7 Thermometry, thermometer, temperature
4.14 Test a liquid in glass thermometer
4.15 Thermoscope to compare absorption of radiation
22.7.0 Thermometers
22.7.1 Temperature sense, feeling "warm" and "cold", measure temperature correctly only with thermometer
22.7.2 Expansion of liquid in a thermometer
22.7.3 Thermometer test, calibrate a thermometer
22.7.4 Thermometers, 0oC to 100oC range
22.7.5 Thermometer, make a thermometer
22.7.6 Thermocouple, thermistor, optical pyrometer, constantan
22.7.7 Galileo's thermometer
22.7.8 Air thermometer
2.8 Pressure affects the boiling point
Use a flask with a 1-hole stopper with a thermometer in it. Fill a flask 3/4 full with water, add boiling chip, heat until boiling, read the temperature, about 100oC. Invert the flask and hold it under a cold stream of water. The water boils again. Read the temperature, less than 100oC. Again invert the flask and hold it under a cold stream of water. The water boils again. Read the temperature, less than before. When the flask is cooled off with the cold water, water vapour in the flask above the water condenses on the colder surface of the flask, a partial vacuum forms and the pressure inside the flask decreases. Water boils at 100oC at standard pressure, i.e. 760 mm mercury or the pressure at sea level. If the pressure is lower the boiling point is lower. So it is hard to make a good cup of tea on a high mountain because the water boils at such a low temperature.
2.112 Temperature sense, feel temperature
Check if your temperature sense is reliable. Use containers of hot water, warm water and cold water. Put both hands in the warm water. The hands feel the same temperature. Put one hand in the hot water and the other hand in the cold water. Quickly dry your hands and put them both into the warm water again. The two hands do not feel the same temperature. Is your temperature sense reliable? This may be a silly experiment but it shows that our temperature sense is not always reliable. You must use thermometers for experiments.
2.113 Thermometer, expansion of liquid in thermometer
Fill a flask with coloured water. Insert a one hole stopper carrying a 30 cm length of glass tubing until the water rises 5 cm in the tubing. Put the flask in a beaker of water. Heat the beaker and observe the water level in the tubing. The water rises in the tubing. However, if you carefully observe the water level in the tubing when the heating begins, you will see that it falls slightly and then begins to rise! It falls because the glass in the flask starts to expand before the water inside. When the heat energy reaches the water it expands. So the expansion of liquid you see in a thermometer is really the expansion of liquid less the expansion of the glass tube.
2.114 Spirit thermometer Experiment deleted!
Make a spirit thermometer by blowing a bulb in one end of the tubing, inverting the open end of the tube in alcohol. Alternately heat and cool the bulb to draw alcohol into the tube, then calibrate in containers of water of known temperature. However this activity is too dangerous for schools especially when it comes to heat sealing the tube.
2.115 Test a thermometer
Use a thermometer with a scale, e.g. thermometer -10oC to 110oC mercury or alcohol, or a tall flask containing coloured water fitted with a one hole stopper and glass tube that extends into the bottle. Mark thermometer scales at two fixed points. The lower fixed point is the temperature of melting ice. Put the bulb of a thermometer in crushed ice that is melting. Leave it there for some minutes. Check that the temperature is 0oC on the calibrated thermometer, or make a mark on the blank scale or on the glass tube attached to the small flask. The upper fixed point is the temperature of boiling water. Put a thermometer in steam immediately above the surface of boiling water. Leave it there for some minutes. Check that the thermometer reads 100oC on the calibrated thermometer, or make a mark on the blank scale or on the glass tube attached to the small flask. Divide the distance between the upper and lower fixed point to obtain marks representing a temperature difference of 1oC. If you do the experiment on a mountain at high altitudes the temperature of boiling water may be below 100oC because of the reduced atmospheric pressure. If you do the experiment in a submerged submarine the temperature of boiling water may be above 100oC. The thermometer in the boiling water reads exactly 100oC only at sea level or where the barometer reading is 760 mm of mercury.
Quantities of heat
2.135 Heat and temperature
Suspend a tin containing 50 mL water and a thermometer over a small Bunsen burner flame or a candle. Record the initial temperature. Heat it for two minutes, constantly stirring, and record the final temperature in degrees Celsius. Empty the water and repeat the experiment with 100, 150, 200 mL water, using the same flame. It is sufficiently accurate to count 1 mL water as 1 g. Find the product of mass of water multiplied by rise in temperature in each case. As the same heat is given out by the flame to each mass of water, the result suggests that a convenient unit of heat would be that absorbed by 1 g water rising in temperature by 1oC. This unit is called a gram calorie. You may see "Kilocalories" quoted in nutritional information, but the SI unit the joule, J, has replaced the calorie. The 15o calorie is the heat to raise the temperature of 1 g water by 1oC at 15oC = 4.1855 J. So 1 calorie = about 4.2 J. The joule, J, is the SI unit of work and energy. A joule is equal to the amount of work done when the point of application of a force of one newton moves one metre in the direction of the force.
1 joule = 107 ergs = 0.2388 calorie. The c.g.s. unit, the calorie, is the amount of heat required to raise the temperature of 1 gram of water by 1oC, i.e. 1K.
Nowadays the SI unit the joule, J, is used. 1 calorie = 4.1876 joules, commonly, 4.2 joules.
7.4.0 Melting point of solids
The melting point, m.p., is the temperature at which a solid starts to liquefy. The melting point and freezing point of a pure substance are the same temperature. Melting is the "solid to liquid" type of phase change. Other phase changes include change from liquid to solid - freezing, solid to gas - sublimation, liquid to gas - evaporation, gas to liquid - condensation. Pure substances melt at constant temperature. Impurities lower the melting point. Impure substances, e.g. alloys, melt over a range of temperature. The melting point graph for a pure substance is horizontal as the solid melts. The melting point graph for an impure substance has an inclined line as the solid melts. Melting points and melting behaviours can be used to identify a substance and decide if it is pure. Melting is also called fusion and the melting point can be called the fusing point.
8.1.1 Candle
See diagram 22.1.1
A flame is a region where a gas emits light because of the high temperature. Candles are usually made of paraffin wax that is a residue from the distillation of petroleum. With enough air, the wax burns to form carbon dioxide and water. With insufficient air, the wax burns to form carbon monoxide and smoke containing carbon. The teardrop shaped flame is called a diffusion flame because oxygen diffuses in form the air to the combustion region and hydrocarbon vapour diffuses out wards form the wick. Heat radiated form the burning wick melts the wax which is drawn up the wick by capillarity. The melted wax vaporizes to form a cloud of hydrocarbon molecules which diffused into the flame and are broken down into small molecules by the intense heat of the flame. The smaller molecules react with oxygen. The smoke from the flame contains carbon particles (soot), water vapour and various products of the reaction of the hydrocarbon particle with oxygen.
8.1.1.1 Parts of a candle flame
The candle flame has three parts:
1. The region closest to the wick is dark in colour because air cannot reach that region, so the gases are not burning
2. The second region is bright yellow- orange and forms much light. Some of the orange and yellow glow is caused by the incandescent soot particles. The red area near the centre of the flame is about 800oC. The outer orange and yellow areas are hotter than this.
3. The third region, the outer rim of the flame, is practically colourless, a very faint blue, and is the hottest part of the candle. The blue colour shows that oxygen is mixing with the wax molecules.
8.1.1.2 Soot from a candle flame
The soot deposited is the carbon used in the manufacture of inks and motor tires. Whenever fuels, e.g. kerosene (paraffin oil) or coal or wood, burn with insufficient oxygen, similar deposits of carbon (soot) can be seen. Hold a glass rod in the centre of the flame. The rod becomes coated with a sooty black film called lamp black (carbon black). Carbon is deposited on the glass rod because not enough oxygen is available for complete combustion.
8.1.1.3 Dark region of a candle flame
Hold a glass tube so that it slants upwards and the bottom end is as close as possible to the wick. Light a match and hold it close to the gases coming out of the end of the tube. Gases burn at the end of the tube. These gases have come from the dark region of the flame where there is not enough air to burn them.
8.1.1.4 Gases from the wick
Light the candle, let it to burn for five seconds and then blow out the flame. Immediately, light a match and hold it near the smoke coming from the wick. This shows that the gases from the wick are flammable.
8.1.1.5 Hold aluminium foil below a candle flame
Cut a slot in a piece of aluminium foil and slide it just below the base of the flame and above the melted wax. The flame dies down or is extinguished because the foil conducts away the heat so the gases cannot be ignited.
8.1.2 Gaseous products of a burning candle
Candle wax is a mixture of different alkanes (paraffins) that are solid at room temperature. Soda lime is a mixture of sodium hydroxide, calcium oxide and calcium hydroxide that absorbs the products of combustion. Use soda lime instead of sodium hydroxide because soda lime is not deliquescent. Weigh a candle. Weigh an U-tube containing granules of soda lime. Put a candle under an inverted glass filter funnel connected to one arm of the U-tube. Attach a filter pump to the other arm to draw air through the U-tube. Light the candle and turn on the filter pump to draw air over the candle. Let the candle burn for five minutes. Extinguish the candle and disconnect the water pump. Weigh the candle again. When the U-tube is cool, weigh it again. The weight of the candle is less. The weight of the U-tube containing the soda lime is greater. The U-tube gains more weight than the candle loses weight for two reasons. The air sucked in by the filter pump contains some water vapour absorbed by the soda lime. To measure the weight of water absorbed from the air, repeat the experiment for the same period, but without the candle. The candle wax combines with oxygen in the air to form carbon dioxide and water.
8.1.4.1 Describe the Bunsen burner flame
See diagram 3.1.1: Bunsen burner | See diagram 3.1.4: Bunsen burner and candle flames
This type of gas burner has a gas jet at the base that draws air in through the air hole because of the Bernoulli effect. It was invented by German chemist Robert Bunsen to improve the efficiency of combustion by combining flammable gas from a jet with air before ignition to give a very hot flame. This premixed flame has a different structure to the diffusion flame of the candle. The blue part of the flame in inside the flame. The flame is conical because of the shape of the rim of the burner. The premixed flame burns efficiently with not much yellow flame or production of soot.
1. Control the amount of air by opening and closing the air hole. Close the air hole. Turn on the gas. Light the gas. The flame is yellow. Hold a piece of wire in different parts of the flame to discover which part is the hottest. Hold a splint in different parts of the flame. The splint can be set alight in all positions in the yellow flame. Hold a test-tube just above the flame. Carbon is deposited on the glass. Test whether the unburned carbon causes the yellow colour of the flame by sprinkling powdered charcoal (carbon) into the flame. Open the air hole. Mixing the air with the gas allows the gas to burn more rapidly and completely. The flame has an outer cone of mainly blue flame and a colourless inner cone. The outer cone has a thin colourless area outside the blue flame. Hold a splint so that it passes through the inner cone of the flame. The middle of the splint does not burn because the inner cone is mainly unburned gas. Hold a piece of wire in different parts of the flame to discover which part of the flame is the hottest. The tip of the colourless part around the outer cone is the hottest part of the flame. The temperature of different parts of a Bunsen burner flame can be measured with a thermocouple.
2. Test the inner cone of the flame
See diagram 3.1.3
Put one end of a piece of glass tubing in the inner cone of the flame. Ignite the unburnt gases that come out of the other end of the tube.
8.1.4.2 Test which part of the Bunsen burner flame is hottest
See diagram 3.1
Add 3 cm of water and small boiling chips to 3 test-tubes. Measure the time taken to boil the water when the bottom of a test-tube is held at the top of:
1. yellow flame - air hole closed, 2. non-luminous (dark blue) flame - air hole open, 3. light blue flame - air hole open. The test-tube held at 3. boils the soonest.
12.1.3 Pressure on solid ice
Use 1 m thin strong steel wire, e.g. piano wire. Attach each end to a broom handle. Loop the wire round a block of ice it and pull tightly so that the wire exerts pressure on the ice. The pressure causes the ice to melt but when the pressure is released the ice becomes solid again. Apply pressure and observe how the wire makes its way slowly through the ice. Similarly a knife forced against ice can exert pressure enough to melt the ice at the edge of the blade. Force cubes of ice together then see them join when the pressure is released and the melted ice freezes again. An ice skater skates on a thin layer of water!
Heat sources
22.1.1 Simple heater
See diagram 22.1.1: Simple heating devices
Use a tin can cover and copper wire to make a handle under the rim of a test-tube. Fill the can of hot water and place the can on a flame to heat the can. Put some material into the test-tube then place the tube into the water at the can. At the liquid heater the material at the bottle may absorb quantity of heat round uniformly. If the material at the test-tube has a higher temperature fill the can of water with the same temperature to that of water at the tube the liquid heater becomes an effective insulator.
22.1.2 Drink-can charcoal burner
See diagram 22.1.1: Simple heating devices
Prepare a large can of diameter at least 10 cm. Draw 6 small windows of regular triangle uniformly on the side of the can and an angle of each triangle just up just towards the bottom of the can. Each window locates at the centre of the side of the can. For each triangular window cut off the two lines of the angle downward then bend the triangular sheet back. The 6 triangular sheets form a stand in the can. Charcoal may be placed on the stand. Polish the windows with a file and drill some air holes. Now a stove has been made.
22.1.3 Make an alcohol lamp, spirit lamp, from an ink bottle
See diagram 22.1.1: Simple heating devices
Use an ink bottle with a screw-on metallic cap; a metallic sheet of 2.5 cm × 4 cm; alcohol; a wick made up of wasted cotton or cotton bath towel of length more than two times of the height of the ink bottle. Drill a hole with a nail in the centre of the cap of the bottle. Use a file to enlarge the hole to diameter 10 mm and use some hard round object (for example round file) to burnish the hole. Roll the small metallic sheet into a cylinder. The outer diameter of the cylinder is equal to inner diameter of the hole on the cap of the bottle. Push the cylinder about 1 cm into the hole on the cap. If possible solder the cylinder on the cap; even the cracks between the cylinder and the cap also are soldered tightly. Insert the wick into the cylinder on the cap and leave a part of fit length outside of the cap and trim the part well. Fill fuel into the bottle but not too full. Screw the cap on the bottle tightly to prevent evaporation.
22.2.0 Heat and temperature, internal energy and heat, thermal physics, Thermal Properties of Matter, heat as a form of energy, distinction between internal thermal energy, heat energy and temperature, heating as the process by which internal energy transfers occur as the result of a temperature difference
See also 23.9.0.1 The Joule / Calorie
Heat is a means by which energy can be transferred. The numerical value for the heat is the amount of energy transferred. Internal energy is the energy associated with the total kinetic and potential energy of all of the molecules of the object. If energy is transferred to an object its internal energy rises. The internal energy would also increase if work were done on the object. The SI unit of heat energy is the joule (i.e. newton.metre). The extent to which an object will transfer or absorb heat (its hotness or coldness) is measured by temperature and is related to the average kinetic energy of its molecules. The process by which the energy is transferred as heat as one of the following three: convection conduction and radiation.
22.2.1 Heat has no weight
The recognition of heat by people in history had experienced a long and tortuous way. So called "heat mass" in general shows a unclear recognition to the character of heat. Heat is a form of energy has no weight. However some students are probably think that heating a beaker will somehow make it lighter. A few may believe that putting "heat in " somehow makes the beaker heavier! Hang a spoon in each end of the cross arm in a stand thread tie to the spoon must be strong enough. Adjust the position of spoon to get them in exactly balance. Record these two positions. Then remove the spoons. Heat one of the spoons by lifting it over an alcohol burner. Put another spoon into cold storage in a refrigerator or cold water (if use refrigerator it is better not to put spoon into freezer). Place the two spoons back to the original position exactly note to affirm the cooled spoon is dry in advance and the position must be original one. To ensure not to confuse them it is better to select the two spoons which have different sizes and shapes or use different colour thread to tie them. If every step is done the whole system is still in balance. To avoid marking in cross arm to mark the original position the cross arm can be replaced by a meter.
1.28 Simple calorimeter
See diagram 22.1.1 | See diagram 22.2.2
1. Use a large-mouth glass bottle for example a large coffee bottle. Use a can with a top only able to be opened by a rotating knife to make sure that the outer rim on the top may be reserved in good order. and if place the bottle into the can make sure that the distance between the bottom of the can and the bottom of the bottle must be more than the distance between the outside of the can and the inner wall of the bottle. so that there is enough air between the can and the bottle to insulate heat. Twine a circle of a narrow piece of foam (or sponge) at the upper outside of the can. Use white adhesive plaster to paste the foam to prevent the foam from slopping. Make a round cover with a white rigid used to pack instrument foam board (or middle density board). Do not use a scroll saw dig a round on the rigid plastic board. You may cut off a square first with a knife cutting paper then cut it into a round. Use 0.15 cm wire to make a beater with a thermometer and brass wires. Drill a hole on the cover. To prevent heat loss paste a circle of silver paper metallic surface inwards then put some paper between the bottle and the can.
2. Simple calorimeter
Small soup tins can be found which fit loosely into a jam jar. If the top of the tin is cut off cleanly with a rotary type opener it serves as an excellent calorimeter. The metal can be prevented from slipping into the jar either by a stout rubber band round the edge, or by cutting nicks in the rim and bending it slightly outwards. This form of suspension, and the low conductivity of glass and air contribute to its efficiency. Expanded polystyrene, Styrofoam, drink cups are available in some countries and make excellent calorimeters. Other suitable calorimeters can be made using two metal cans or glass beakers. Select containers so that one will fit inside the other with at least 1 cm of space between them. Fill this space with glass wool or crumpled paper.
1.29 Measuring jar or 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.
22.2.3 Amount of heat absorbed depends on mass
See diagram 22.2.3
Place a large iron bolt and a small nail in a beaker filled with boiling water. Fill other two beakers with equal masses of cold water at same temperature put a thermometer each. Note that the amount of water is better to just immerse iron bolt. To do this you can test a suitable the amount of water by bolt before experiment. In the process of the experiment let large iron bolt and small nail are in boiling water for a while then take them out of boiling water. Put large one into a beaker small one into another beaker rapidly. Observe the temperature of water rises record the temperature in each beaker after temperature is stable. The different temperature shows the different amount of heat they have. The objects in different masses at the same temperature absorb amount of heat which depend on their mass each.
22.2.4 Heat dissipation
Fill a small and a large round bottom flask with hot water at the same temperature. Insert thermometers in both flasks and note the decrease in temperature as heat is dissipated. Heat dissipation is a function of of the area of the surface. Heat content is a function of he volume of the unit. The area increases as the square of the radius but the volume increases as the cube of the radius.
22.2.5 Heat a solid sphere and a hollow sphere
Put a solid metal sphere and a hollow metal sphere with the same external volume in a beaker of water and heat the water. The expanded external volumes are still the same. Put the two spheres in identical beakers and add the same volume of water heated to the same temperature. The hollow sphere expands more than the solid sphere because its mass is less.
22.7.0 Thermometers
Thermometry, thermometers, temperature scale, upper and lower fixed points, mercury thermometer, alcohol thermometer, clinical thermometer, liquid crystal thermometer
See diagram 22.02
A thermometer uses changes in a selected property to measure changes in temperature e.g. change of length in thermostats change in volume in mercury thermometers change in pressure in gas thermometers change in resistance of wires change in the emf in thermocouples. To calibrate a thermometer in oC the value of the selected property is first found at the ice point and mark this 0oC. Then the value of the property is found at the steam point and mark this 100oC. Divide the change in property between 0oC and 100oC into 100 equal parts each equivalent to a change in temperature of 1oC.
22.7.1 Temperature sense, feeling "warm" and "cold", measure temperature correctly only with thermometer
See diagram: 22.02: Thermometers
1. Check if your temperature sense is reliable. Use containers of hot water, warm water and cold water. Put both hands in the warm water. The hands feel the same temperature. Put one hand in the hot water and the other hand in the cold water. Quickly dry your hands and put them both into the warm water again. The two hands do not feel the same temperature. This experiment shows that our temperature sense is not always reliable.
2. Fill three plastic dishes with the same amount of water but at different temperature 10oC, 20oC, 30oC. To get water at different temperature more accurate first pour some cold water then put heat water stir lightly with a spoon to make temperature evenly. Arrange three dishes from left to right with temperature from low to high. Let two students one put his right hand into 10oC water the other put his left hand into 30oC water. After two minutes take out their hands at the same time swing strength then put hands into dish at 20oC in the middle simultaneously in time. Let each student say the water in the middle dish is warm or cold. The experiment shows that you can judge if an object is warm or cold by our sensation. However, this method is limited to a qualitative judge shows more relatively the degree of warm and cold of an object. The objects which have the same degree of warm or cold can be judged to a different conclusion of degree of warm or cold under different cases. You feel warmer as your hand removes from water in lower temperature to that of higher temperature while you feel colder as your hand removes from water in higher temperature to that of lower temperature. As you can see warm and cold have not a definite standard. This cannot meet the needs of showing degree of warm and cold scientifically. To show the degree of warm and cold of an object quantitatively it is necessary to introduce an important quantity, temperature and make an equipment which can measure the temperature- thermometer.
22.7.2 Expansion of liquid in a thermometer
See diagram 22.3.2
1. Fill a flask with coloured water. Insert a one hole stopper carrying a 30 cm length of glass tubing until the water rises 5 cm in the tubing. Put the flask in a beaker of water. Heat the beaker and observe the water level in the tubing. The water rises in the tubing. However, if you carefully observe the water level in the tubing when the heating begins, you will see that it falls slightly and then begins to rise! It falls because the glass in the flask starts to expand before the water inside. When the heat energy reaches the water it expands. So the expansion of liquid you see in a thermometer is really the expansion of liquid less the expansion of the glass tube.
2. Put some crushed ice in a Erlenmeyer flask add a little water. The depth of mixture in the flask is about one inch. Spin the flask to mix water and ice. Insert a thermometer into the mixture. As the column of liquid in thermometer is stable mark on thermometer beside the scale marked 0oC. Put the flask on wire gauze on a tripod heat it with a burner. As water in the flask boils mark again as 100oC. Note to maintain two marks at the same vertical line. The freezing and boiling point of water are primary standards for calibrating thermometer. Draw a scale of thermometer between 0oC and 100oC divide it into 100 same space draw a longer line every 10 points written as 10oC 20oC draw a shorter line every 5 points written as 5oC, 15oC, 25oC. Compare the scale you have done to original one. Maybe they quite different. The main reason is the scale lines of 100oC are not the same because the atmospheric pressure is not the standard as you do the experiment and the boiling point of water may not exactly the 100oC. To draw line and calibrate easily you can use a sheet of coordinate paper stick to the thermometer in advance.
22.7.3 Thermometer test, calibrate a thermometer
There are two marked points on the scale of a thermometer. If a thermometer can measure the temperature from 0oC to 100oC the two fixed points are at 0oC and 100oC. 0oC is the melting point of ice and 100oC is the boiling point of water. Other scales of temperature are all defined refer to two fixed points. The melting point and boiling point depend on atmospheric pressure so the melting point of ice and the boiling point of water are at standard atmosphere.
1. Use a thermometer with a scale, e.g. thermometer -10oC to 110oC mercury or alcohol, or a tall flask containing coloured water fitted with a one hole stopper and glass tube that extends into the bottle. Mark thermometer scales at two fixed points. The lower fixed point is the temperature of melting ice. Put the bulb of a thermometer in crushed ice that is melting. Leave it there for some minutes. Check that the temperature is 0oC on the calibrated thermometer, or make a mark on the blank scale or on the glass tube attached to the small flask. The upper fixed point is the temperature of boiling water. Put a thermometer in steam immediately above the surface of boiling water. Leave it there for some minutes. Check that the thermometer reads 100oC on the calibrated thermometer, or make a mark on the blank scale or on the glass tube attached to the small flask. Divide the distance between the upper and lower fixed point to obtain marks representing a temperature difference of 1oC. If you do the experiment on a mountain at high altitudes the temperature of boiling water may be below 100oC because of the reduced atmospheric pressure. If you do the experiment in a submerged submarine the temperature of boiling water may be above 100oC. The thermometer in the boiling water reads exactly 100oC only at sea level or where the barometer reading is 760 mm of mercury.
22.7.4 Thermometers, 0oC to 100oC range
First put thermometer into crushed ice after a few minutes observe if the liquid column in the thermometer is exactly at 0oC. Take out the thermometer from the ice wait for a while at the temperature of surroundings. Put the thermometer on the surface of boiling water the measuring bulb is near the heat steam above the surface of water. Wait for a few minutes observe if the liquid column in the thermometer is at the scale of 100oC. Note if you live in the region of higher height above sea level the boiling point of water there will be lower than 100oC due to the lower atmospheric pressure. On the contrary in the region of lower height above sea level the boiling point of water will be higher than 100oC. Only in height of sea level the boiling point of water is just 100oC the atmospheric pressure there is 760 mm Hg.
22.7.5 Thermometers, make a thermometer
Prepare a small glass bottle with a rubber stopper which is punched a hole and installed a thin glass tube long enough. This is a thermometer the small bottle is a measuring bulb the thin glass tube is a pole. Pour a few drops of red ink in the water close the stopper to make no air inside the bottle. The glass tube must be sealed by stopper as tightly as possible until surface of water cannot rise up. Mark 0oC and 100oC according to the steps above. If it is not possible to measure 0oC and 100oC because of the limit of level of water and size of tube, you can select two suitable temperature points by yourself. However, but this time you must find the temperature by means of a accurate thermometer. Measure the length between 0oC to 100oC on the glass tube divide the length into 10 evenly and mark on the wall of the tube. (i.e. mark 9 points in same distance each other between 0oC to 100oC). Write 10oC to 90oC in turn i.e. every space is 10oC. You may divide by 10 again between every space and mark it. This time every space is 1oC. So a thermometer is finished. If you live in the region of higher height above sea level you should correct fixed point of 100oC according to the boiling temperature there.
22.7.6 Thermocouple, thermistor, optical pyrometer, constantan
A thermocouple has two different wires or semiconductors joined at the ends to be a thermoelectric source of EMF, Seebeck effect, when the wires are at different temperatures. It is used to detect very small differences in temperatures. For more sensitivity thermocouples are joined in series to make a thermopile, pile. Thermistors are wires used in electronic circuits made of metal oxides that decrease in resistance when the temperature of the wire increases. An optical pyrometer is used to measure very high temperatures from the colour of the radiant heat source.
1. Attach a piece of copper and a piece of constantan (50-60% copper 40-50% nickel alloy) to two wires. Heat lead to above its boiling point of 327oC. Attach the wires to a galvanometer and insert the copper and constantan into the boiling lead. The galvanometer can be calibrated to read temperature and act as a thermocouple to read the temperature of the molten lead.
22.7.7 Galileo's Thermometer
Use a set of glass spheroid buoys of varying density in a glass cylinder arranged so the lowest floating ball represents the temperature.
22.7.8 Air thermometer
See diagram 23.4.9
Select a small medicine bottle with a cork stopper. Bore a hole through the cork with a cork borer to take a piece of thin glass tubing 30 cm long. Put ink in the bottle to cover the end of the tubing, which should be touching the bottom of the bottle. Warm the bottle with your hands to make the air in the bottle expand, press down on the liquid in the bottle and force it up the glass tube.