The 1827 Christmas Lectures
of Michael Faraday

Demonstration of Lecture #2 Today

Atmospheric Air and its Gases

FARADAY'S SECOND LECTURE IN MODERN PEDAGOGY

Today's teacher reveals to his audience the properties and composition of the atmosphere using a discussion/demonstration format. The atmosphere is described by the physical properties of mass, volume, elasticity, density, expansion and pressure. Processes of combustion, respiration and photosynthesis demonstrate the chemical properties, composition and dependence of life on the atmosphere.

OBJECTIVE ONE: Student describes air as being composed of matter having mass and occupying space.

EXPERIMENT	FAN - OPEN WAFTED HAND

OBJECTIVE TWO: Student compares the density of air with liquids and solids.

EXPERIMENT	JAR WITH STONES, WATER, FLOATING BULB, HELIUM BALLOON

OBJECTIVE THREE: Student comprehends the elasticity of air and contrasts this property with the action of a spring.

EXPERIMENT	SPIRAL SPRING/SYRINGE/SPRING WITH WEIGHT ON AND OFF

OBJECTIVE FOUR: Student identifies the relationship of a force per unit area with pressure.

EXPERIMENT	FLASK WITH BALLOON
EXPERIMENT	BLADDER OF AIR

OBJECTIVE FIVE: Student relates the effect of changes in temperature on a volume of air.

EXPERIMENT	AIR THERMOMETER

OBJECTIVE SIX: Student describes the processes of combustion.

EXPERIMENT	SYNTHESIS/DECOMPOSITION OF WATER ELECTROLYSIS

OBJECTIVE SEVEN: Student identifies the two major components of air (oxygen and nitrogen).

OBJECTIVE EIGHT: Student understands several methods of preparing and testing for oxygen and nitrogen.

EXPERIMENT	NITROGEN AND OXYGEN PREPARED. DIFFERENCES DEMONSTRATED.

OBJECTIVE NINE: Student recognizes the proportion of nitrogen to oxygen in air.

EXPERIMENT	ALCOHOL IN LARGE CONTAINER/ALCOHOL-WATER IN LARGE CONTAINER
EXPERIMENT	THE ACTIVITY OF A PREPARATION OF AIR IN 1:4 PROPORTION COMPARED WITH THE ACTIVITY OF A PREPARATION OF PURE OXYGEN

OBJECTIVE TEN: Student describes the evidence supporting the existence of water in the atmosphere.

EXPERIMENT	PITCHER OF ICE COLD WATER

OBJECTIVE ELEVEN: Student describes the evidence supporting the existence of carbon dioxide in the atmosphere.

EXPERIMENT	TEST FOR THE PRESENCE OF CARBON DIOXIDE IN AIR -- LIMEWATER

DEMONSTRATIONS TO BE GIVEN

OBJECTIVE ONE: FLUIDITY AND MOTION OF AIR

PURPOSE	to illustrate the motion of air and the ability of matter to move freely in air.
MATERIALS	Finely divided particles of polystyrene
PROCEDURE	Propel the particles through the air -- the method may be as simple as blowing a small amount from your hand or you could use an electric fan or pressurized gas for a more dramatic effect. Alternatively place the styrofoam in a clear 2 L bottle and direct a stream of gas into the neck of the bottle. This should help control the scattering of the particles.
DISCUSSION	Note the invisible nature of air, allowing free motion, but providing some support.
HAZARDS AND DISPOSAL	There are no hazards. Collect and reuse the polystyrene.

OBJECTIVES TWO AND FOUR: RELATIVE DENSITY OF SOLID, LIQUIDS AND GASES

PURPOSE	to contrast the density of gases to solids/liquids.
MATERIALS	1L beaker, straws, stones, pieces of common metals, food color, vegetable oil, and a He balloon.
PROCEDURE	Add stones and metals to 1L beaker of water. Blow air through the straw into the bottom of the beaker. Compare density of solids/liquids/air. Add food color to water, mix, and carefully add oil to the top of the water. Place a piece of styrofoam or cork in the beaker. Repeat step #2. Release a He balloon, compare densities of gases.
HAZARDS	There are none.
DISCUSSION	Use oil as an example of a liquid less dense than water. Add styrofoam or cork as an example of a less dense solid. Show image of cork or styrofoam under magnification to show air pockets if desired.

OBJECTIVE THREE: COMPARISON OF AIR ELASTICITY AND A MECHANICAL SPRING

PURPOSE	To illustrate the elasticity of gases.
MATERIALS	large graduated plastic syringe spiral spring metal weights and hangers
PROCEDURE	Secure syringe and spring vertically to a horizontal support. Apply weights to pull on spring and syringe. Measure the change in vertical displacement of the spring and syringe. Release the weights.
HAZARDS	None.
DISCUSSION	As a simple alternative you may wish to pull down on the syringe and spring (without the use of weights) to demonstrate the concept at a qualitative level.

OBJECTIVE SIX: ELECTROLYSIS OF WATER

PURPOSE	To show the elemental components of water; to show the decomposition of water by use of electricity.
MATERIALS	1 9-volt battery water 1 battery clip potassium sulfate 2 alligator clips bromothymol blue 2 pencils with both ends sharpened shallow glass dish
PROCEDURE	Attach the end of the sharpened pencil (graphite) by the alligator clip to the battery cap, repeat with second pencil. Add water to a depth of about 5 cm in the glass dish, add a small amount of potassium nitrate to the water and add a few drops of bromothymol blue. Carefully place each pencil into the dish (don't let electrodes touch). Connect the entire set-up to the battery. Observe.
DISCUSSION	This is a ``homemade'' inexpensive version of the Hoffmann apparatus. The water is undergoing electrolysis: H+/H2O is reduced to H2 and oxidized to OH-/H2O2 oxidized to oxygen. 2H2O(l) = 2H2(g) + O2(g) The potassium sulfate in the water acts as an electrolyte. The gases collect in the test tubes by water displacement. A glowing splint is the traditional test for the presence of hydrogen (pops) and the presence of oxygen (bursts into flame).
HAZARDS AND DISPOSAL	None.

OBJECTIVE EIGHT: PROPERTIES OF NITROGEN AND OXYGEN

PURPOSE	To illustrate the differences in chemical and physical properties of nitrogen and oxygen.
MATERIALS	A small Dewar flask filled with liquid nitrogen, large test tube, wood splints, matches.
PROCEDURE	Immerse the test tube well into the liquid nitrogen and allow it to stand for 5-10 minutes. At the very cold temperature of liquid nitrogen, oxygen, together with a little nitrogen, will liquefy in the test tube. When sufficient liquid has collected, remove the test tube to a test tube rack and thrust a lighted wood splint into the gas above the liquid air. The flame will be extinguished because the nitrogen fraction of the liquid air boils off first at 77K. When the liquid air is nearly all gone, try the test again with a glowing (not burning) wood splint. The splint will relight because the nitrogen is gone and the liquid oxygen is now boiling at 90K.
DISCUSSION	You can set this up just before the lecture and allow the air to liquefy until you are ready for it. Stress that you have demonstrated both a chemical difference (ability to support combustion) and a physical difference (boiling point) in the two gases.
HAZARDS AND DISPOSAL	Do not allow liquid nitrogen to come into contact with skin or clothing. Pour the leftover liquid nitrogen onto the floor. Do not allow it to stand open to the atmosphere unattended too long as oxygen will condense in it and present a possible fire hazard.

OBJECTIVE NINE: THE PREPARATION OF AIR

PURPOSE	To prepare air in the laboratory by generating and combining gaseous oxygen and nitrogen in the ratio 1:4.
MATERIALS	6 gas collecting bottles 2 one-hole rubber stoppers to fit bottles rubber tubing 1 pneumatic trough 2 large test tubes as gas generators glass plates labels grease pencil wood splints 3% hydrogen peroxide MnO2 liquid nitrogen water
PROCEDURE	Preparation of oxygen and nitrogen Assemble the apparatus for the collection of a gas by the water displacement method. Label two bottles as pure O2; two bottles as pure N2, and two bottles as ``air''. Measure the total volume of the gas bottles by filling them with water and mark them in increments of fifths. These bottles will be used to mix the ``air''. Combine 25 mL of H2O2 and 2.00 grams of MnO2 (catalyst). The oxygen will immediately begin to be generated. Allow some time for the air in the line to be purged. Collect two bottles of pure oxygen. Set aside. Use the bottles labeled ``air'' and fill them to the one-fifth mark with O2. Set aside. Place approximately 20 mL of liquid nitrogen in the second clean, dry large test tube. Stopper the test tube with the delivery apparatus. Allow the liquid to vaporize. This is the source of nitrogen. Collect two bottles of pure nitrogen and set them aside. Replenish the liquid nitrogen if necessary. Use the bottles labeled ``air'' and add nitrogen for the remaining four-fifths. Remove all gas-filled bottles with the glass plates. There are now two bottles of pure oxygen, two bottles of pure nitrogen, and two bottles of ``air''. Test each bottle with a burning wood splint. Observe and record. Repeat step #10 using a glowing wood splint.
DISCUSSION	The burning wood splints will continue to burn in ``air'', will be extinguished in the pure nitrogen and will burn brilliantly in the pure oxygen. Pure oxygen supports combustion and pure nitrogen does not. Since ``air'' is a mixture of these two gases, the intensity of the combustion will be diminished. The glowing splints will not re-ignite in ``air''; will burst into flames in the pure oxygen, and will be totally extinguished in the pure nitrogen.
HAZARDS AND DISPOSAL	3% hydrogen peroxide is an oxidizer and a skin and eye irritant. MnO2 is a strong oxidant; avoid contact with organic material; moderately toxic. Filter out MnO2 and dispose in solid waste disposal landfill. Pour fluid down the drain with excess water.

OBJECTIVE NINE: THE SIMPLEST JET ENGINE

PURPOSE	To illustrate the diminished combustibility of alcohol when mixed with water and to compare it to the diminished activity of oxygen when mixed with nitrogen in the atmosphere.
MATERIALS	5-gallon water cooler container 30 mL ethanol (or isopropyl alcohol?) 20 mL water
PROCEDURE	Add 25 ml of ethanol to a dry water cooler container and swirl liquid to vaporize alcohol. Pour off unvaporized alcohol. Drop lighted match into container (caution: stand back!) Repeat steps 1-3 using a mixture of 20 mL water and 5 ml ethanol.
DISCUSSION	The vaporized ethanol in step 3 will immediately combust, creating a wonderfully brilliant vortex of flame and a roaring sound as oxygen is drawn into the container. The diluting effect of the water will be evident in step 4 with a much reduced combustion. The diluting effect of the water on the alcohol is analogous to the effect nitrogen has on oxygen in the atmosphere. The oxidation of iron in pure oxygen is dramatic in comparison with the much slower oxidation of iron in ordinary air.
HAZARDS AND DISPOSAL	The reaction is quite violent and should be done behind a clear barrier. No disposal problems.

OBJECTIVE TEN: MOISTURE IN AIR

PURPOSE	To demonstrate that there is water vapor in the air.
MATERIALS	pitcher of ice water glass of iced tea or soda (optional) anhydrous copper sulfate
PROCEDURE	Place the full pitcher of ice water on top of a table so the audience can see it. Point out that the surface of the pitcher appears to be frosted. Ask the audience what causes the cloudy film on the surface of the pitcher. Students should realize that moisture condensing on the surface of the cold pitcher causes the cloudy film. Water from the air is being condensed because of the low temperature of the outside surface of the pitcher. Sprinkle the anhydrous copper sulfate on the outside surface of the pitcher. Note the color change from dingy white to bright blue.
DISCUSSION	As the warm air comes into contact with the cold glass surface, the water vapor condenses onto the glass. Copper sulfate anhydrous, as it absorbs water changes from white to blue, which suggests that the liquid is water.
HAZARDS AND DISPOSAL	There are no hazards associated with this demo. Disposal down the sink.

OBJECTIVE ELEVEN: TO DEMONSTRATE THAT AIR CONTAINS CARBON DIOXIDE

PURPOSE	To demonstrate that air contains carbon dioxide.
MATERIALS	Ziplock baggie (quart size) 200 mL limewater straw
PROCEDURE	Pour 200 mL of water into the Ziplock baggie and zip it shut, except for small opening for a straw. Insert a straw through the opening and blow gently into the limewater. Continue blowing until you can detect a white cloudy precipitate. Strictly speaking this demo shows the presence of CO2 in exhaled, not ordinary, air. For the latter, use a water pump to draw ordinary air through limewater. Because of the small amount (3.4 x 10-2 per cent) of CO2 in ordinary air, formation of visible amounts of CaCO3 may take some time.
DISCUSSION	The reaction is the following: CO2(g) + Ca(OH)2(aq) --> CaCO3(s) + H2O(l) The precipitate that forms is calcium carbonate.
HAZARDS AND DISPOSAL	There are none associated with this demo. Disposal down the sink.

ADDITIONAL ACTIVITIES

A. NOT ON THE LEVEL

PURPOSE	To demonstrate the property of density.
TIME	15 minutes
MATERIALS	bought or homemade U-tube food coloring rubbing alcohol saturated salt solution
HAZARDS	None.
PROCEDURE	Pour water into one side of the U-tube until it is about 1/2 full and observe how the water levels of the two sides of the tube are even. (OPTIONAL: add food coloring to the water to make it more visible.) If you are using a glass U-tube, clamp it to the ring stand to minimize mixing during pouring. Slowly pour the saturated salt water solution (or isopropyl alcohol) into one side of the U-tube until the liquid on one side of the tube is within 2 cm (1 inch) from the top of the tube. Do not mix the solutions. The surface of the salt solution is below the level of water on the other side. (If isopropyl alcohol is used, the alcohol side will be higher than the water side.) If alcohol and water are used, the interface between the two liquids may be visible initially; after a day, no interface is observed. If left undisturbed, the levels will remain different for quite some time.
DISPOSAL	No special precautions necessary.
DISCUSSION	When you first add water to the U-tube, notice that the water level is the same on both sides. The water levels on both sides of the tube are even since they are exposed to the same atmospheric pressure. When, without mixing, you add the second liquid (saturated salt solution or isopropyl alcohol) to one side of the U-tube, the two levels of the U-tube are no longer equal because the two liquids have different densities. Saturated salt water is more dense than water. A given mass of the salt solution displaces the same mass of water. Since water is less dense than the salt solution, the volume of water displaced will be greater than the volume of salt solution added, and the water level will be higher than the saturated salt solution level. The opposite phenomenon occurs with isopropyl alcohol. The alcohol is less dense than water, so the alcohol side is higher than the water side.
MAKING THE HOMEMADE U-TUBE	Bend the piece of plastic tubing into a ``U'' shape. Place it on the center of a piece of pegboard. Fasten the U-shaped tube onto the pegboard by twisting 3 pieces of wire or garbage-bag ties around the tube and through the pegboard.
MAKING THE SATURATED SALT SOLUTION	Stir 3 tsp of salt into 1/4 cup of water for at least five minutes. Allow any undissolved salt to settle to the bottom. Use only the clear, colorless, salt solution. Discard the undissolved salt.

B. DENSITY BOTTLE

PURPOSE	To help students understand the property of density.
TIME	N/A
MATERIALS	2 liter bottle paint thinner food coloring
HAZARDS	None.
PROCEDURE	Use a 2 liter plastic bottle and fill half full with colored water. Fill the rest with paint thinner (mineral spirits).
DISPOSAL	No special procedure is necessary.
DISCUSSION	Use as a demonstration when describing densities of various liquids. Having this available throughout the year is a convenient way for students to get hands on experience in considering densities.

C. UNDERWATER CARDS

PURPOSE	To demonstrate how surface tension and air pressure can keep water from falling out of an inverted cup covered with a playing card.
TIME	10 minutes
MATERIALS	glass jar playing card or piece of paper large enough to cover the mouth of the jar water
HAZARDS	None.
PROCEDURE	Fill the jar about 1/2 full of water. Be sure the jar is held over a sink or container. Holding the card over the mouth of the jar, invert the jar. Release the card. The water should remain in the jar.
DISPOSAL	No special procedure is necessary.
DISCUSSION	The same effect can be produced by inverting a nipple-capped baby bottle half-filled with water. After a few moments dripping ceases. Air pressure helps this work. When the jar is inverted, a few drops of water leak from the jar, causing the air pressure inside the jar to decrease. The air pressure outside the jar pushes the card against the mouth of the jar, preventing the water from falling out of the jar. If an absorbent paper is used to cover the mouth of the jar, some water will soak into the paper lowering the air pressure in the jar.

D. POP BOTTLE RACE

PURPOSE	To show how air pressure allows liquids to be poured from containers.
TIME	15 minutes
MATERIALS	two 2-liter plastic pop bottles filled with water 2 sinks or pans into which the water is poured
HAZARDS	None.
PROCEDURE	This is a contest between two volunteers. They are to empty their bottles as fast as they can. One can only turn the bottles upside down and shake. The other will be trained ahead of time to swirl the bottle to make a ``tornado''. The tornado volunteer will finish in approximately half the time.
DISPOSAL	Mop floor.
DISCUSSION	The swirling of the bottle allows a small but important passageway for air to enter the bottle and help ``push'' the air out of the bottle. The other bottle has to ``gulp'' air in bunches, interfering with the escape of the water.

E. CARTESIAN DIVER

PURPOSE	To show the effect of pressure on the volume and density of a gas, and to show why objects float.
TYPE	Demonstration
TIME	15 minutes
MATERIALS	1 clear liter size (or larger) plastic bottle 1 medicine dropper than fits into the bottle 1 tall glass water
HAZARDS	None.
PROCEDURE	Fill the large bottle to the top with water. Put a medicine dropper into a glass of water and adjust the water level inside the dropper until it just barely floats. Carefully transfer the dropper to the bottle. Fill the bottle to the very top with water, making sure there are no air bubbles trapped inside. Screw on the top of the bottle. Squeeze the bottle. (The dropper sinks.) Release the pressure on the bottle. (The dropper rises.)
DISPOSAL	No special procedure is necessary.
DISCUSSION	When you exert pressure on the sides of the bottle, the volume of air inside the dropper decreases and the water level inside the dropper increases. This makes the dropper system more dense than the surrounding water, so the dropper falls. When pressure is released, water leaves the dropper as the air inside the dropper expands. The dropper is now as buoyant as when you started, so the dropper rises.

F. EGG IN A BOTTLE

PURPOSE	To illustrate a difference in air pressure.
TYPE	Demonstration
TIME	15 minutes
MATERIALS	quart milk bottle or an 8 oz. glass baby bottle (glass bottle with an opening slightly smaller than the diameter of the egg paper (about a fourth of an 8 1/2 x 11 sheet) matches hard-boiled egg peeled and oiled with vegetable oil
HAZARDS	Be careful when lighting the paper.
PROCEDURE	Bring a previously hard-boiled egg to the classroom. Peel and wipe the egg with vegetable oil. Rest it on the mouth of the milk bottle. Remove the egg, crumple up the paper, light it with the match and drop it into the bottle. Immediately place the egg back on the bottle, narrow end downward. Observe the egg fall into the bottle. To remove the egg, first, rinse out the burnt paper with water. Then hold the bottle upside down so that the egg is at its mouth. Press your lips hard against the mouth of the bottle and blow into it as hard as you can. Out comes the egg!
DISPOSAL	No special procedure is necessary.
DISCUSSION	To get the egg into the bottle, you need to heat the air inside the container. This causes the air to expand and some of it escapes, reducing the air pressure inside the bottle. By placing the egg over the mouth of the bottle before outside air could enter, some of the gases are pushed out past the egg by the pressure resulting from an increased temperature. The egg acts as a one-way valve. The greater pressure of the air outside the bottle forces the egg down into the bottle. The gases in the bottle contract, forming a partial vacuum. Of course, the pressure inside the bottle will become equal to the air pressure outside it as soon as the egg no longer blocks the mouth. The egg will not fall out even if you turn the bottle upside down. To remove the egg, you increase the air pressure in the bottle. The egg falls out as soon as you take your mouth away from the rim because the air flows past the egg, forming higher air pressure behind the egg.

G. MOVING MOLECULES

PURPOSE	To demonstrate the molecular motion of solids, liquids, and gases.
TYPE	Demonstration
TIME	20 minutes
MATERIALS	3 Petri dishes with lids steel shot ( or BB's) overhead projector safety glasses broom and dust pan
HAZARDS	Safety glasses should be worn to prevent eye injury from the steel shot as they fly out of the Petri dish. Make sure all students are at least several feet away from the overhead projector and clear from any flying shot. All steel shot should be cleaned off the floor to prevent slipping on them.
PROCEDURE	In the first Petri dish, add enough steel shot to make one layer covering the entire bottom. (This will represent the solid phase.) Fill the second Petri dish about 1/3 full of steel shots to represent the liquid phase. For the gas phase, put only about ten steel shots in the third Petri dish. Put the lids on each Petri dish and place them on the stage of the overhead projector.
DISPOSAL	No special procedure is necessary.
DISCUSSION	Tell the students that each Petri dish simulates a different phase of matter, either solid, liquid, or gas. Ask the students to decide which Petri dish represents each phase of matter. This can lead to a detailed discussion of the arrangement of molecules in each phase of matter. Now take the model and discussion a step further by moving the Petri dishes in a way as to represent the type of molecular motion associated with each phase. Move the solid phase Petri dish back and forth to represent the vibrational movements of a solid. Discuss how solids have a definite volume, very little space between molecules and, therefore, can only vibrate in place. For the liquid phase, move the Petri dish back and forth to show the vibration and at the same time rotate it to represent the motion of liquid molecules. Discuss how liquids have a definite volume but not a definite shape; thus they are able to flow freely. The molecules are also farther apart which allows them to move more than solid molecules. For the gas phase, move the Petri dish back and forth in a circular motion, and then much more rapidly and randomly to represent the molecular motion of gas molecules. Point out to the students that large spaces between molecules, the constant rapid motion, and random collisions. Ask the students what would happen to the gas molecules (steel shot) if you were to take the lid off the Petri dish. The students won't expect you to actually do this, but after making sure the students are several feet away from the overhead projector remove the lid. Continue vibrating the Petri dish rapidly and randomly. The students will enjoy watching the gas molecules (steel shot) fly out of the Petri dish. Now discuss how a gas has no definite volume or shape. The shot or molecules essentially patrol the container and when you remove the lid they immediately start patrolling their new container - the room! This would also be a good time to talk about diffusion. Remember to sweep the floor before the class is over. You don't want to demonstrate a student slipping on a gas molecule.

H. EGG SUCKER

PURPOSE	To demonstrate the use of a vacuum.
TIME	15 minutes
MATERIALS	raw egg Erlenmeyer flask vaseline or vacuum grease paper or cotton ball alcohol
PROCEDURE	Use a file or some other sharp object to poke a pinhead size hole in each end of the raw egg. Prepare a one liter Erlenmeyer flask by coating the upper lip with vaseline or vacuum grease to help seal the egg. Ignite a piece of paper or, if you want better suction, use a cotton ball soaked in alcohol. Drop the burning material into the flask. Quickly place the egg over the top of the flask. If you have a good seal, in a few seconds the juice will be sucked out of the egg.
DISPOSAL	No special procedure is necessary.
DISCUSSION	This is a neat twist on the hard-boiled egg trick.

I. DANCING RAISINS

PURPOSE	To demonstrate how change in density can make an object sink or float.
TIME	10 to 15 minutes
MATERIALS	Hard dried raisins or uncooked popcorn or macaroni. Tall clear jar containing chilled colorless carbonated beverage (e.g.; club soda, 7-Up, Alka Seltzer)
HAZARDS	None.
PROCEDURE	Pour carbonated beverage into the clear jar. Add the raisins, uncooked popcorn or macaroni. Observe the raisins sinking, and then rising to the surface. They will spin, sink, and float to the surface over and over again.
DISPOSAL	No special procedure is necessary.
DISCUSSION	Raisins are more dense than the beverage and will sink when dropped into the beverage. The carbonated gas, carbon dioxide (CO2), forms bubbles at the bottom of the jar. Bubbles attach to the raisins. The attached bubbles cause a net change in density, so the pieces rise. At the surface of the liquid the bubbles break and the gases are released to the air. As the bubbles are released, the raisin spins if there are more bubbles on one side of the raisin. After losing the attached bubbles, the raisins sink to their natural level -- the bottom. This process is repeated again and again.

J. DENSITY COLUMN: RED, WHITE AND BLUE

PURPOSE	To show that different substances have different densities, that the order that the substances are poured into a jar does not affect their relative positions in the jar, and that some substances are immiscible.
TIME	20 minutes
MATERIALS	white Karo syrup red food coloring blue lamp oil powdered milk large jar water
HAZARDS	None.
PROCEDURE	Before demonstration add food coloring to syrup. The easiest way to do this is to pour syrup out of the jar into a container, add the food coloring, and return it to the original container. This is a bit messy but it is almost essential to obtain a nice uniform red color. Mix some of the powdered milk with water according to the box. (Liquid milk in bottle or can will work also but is more difficult to store.) Place jar in front of students and pour the three liquids into it in any order. OBSERVE. Invert the container. OBSERVE. This will stay for two days without significant mixing.
DISPOSAL	No special procedure is necessary.
DISCUSSION	The order of densities of the liquids from highest to lowest is: Karo syrup, milk, lamp oil. The Karo is always on the bottom of the density column, even when it is inverted. Even though syrup and milk will form an homogenous mixture with constant mixing, they will not mix quickly in this demonstration. Colors may be chosen to coincide with the season. For example, red lamp oil and green food coloring at Christmas or orange food coloring, yellow lamp oil, and black poster paint added to milk for Halloween.

K. HEATING AND COOLING A GAS

PURPOSE	To demonstrate Charles' Law.
TIME	15 minutes
MATERIALS	balloon flask hot plate water
HAZARDS	None.
PROCEDURE	Place a small amount of water in the bottom of the flask and heat it to a full boil for at least one minute. Remove the flask from the hot plate. Immediately stretch a balloon over the neck of the flask. Take care not to scald your hands. Allow the flask to cool.
DISPOSAL	No special procedure is necessary.
DISCUSSION	The balloon first expands and then contracts. Eventually the balloon is pulled, inside out, down into the flask. Ask students the following: What was in the flask when the balloon was attached? (Water, water vapor, and possibly a little residual air.) What made the balloon first expand and then contract? (The water vapor from the boiling water replaced most of the air in the flask before the balloon was attached. When the balloon was first attached, some of the water was still vaporizing so the volume of gas was increasing and the balloon expanded. As the flask cooled, the water vapor condensed. A partial vacuum was created inside the flask and the outside air pressure collapsed the balloon.

L. PTV MADE SIMPLE

PURPOSE	To show the relationship between pressure, temperature and volume.
TIME	Five minutes
MATERIALS	cardboard pencil scissors
PROCEDURE	Take a large index card and write P, T, and V equally spaced and across the card. Punch a small hole below each symbol. Rotate the card on a pencil to show what happens when one variable stays constant and the other two change.
DISCUSSION	Use this activity after your classes understand the gas laws.
HAZARDS AND DISPOSAL	Save the card.

M. TORNADO TUBE

PURPOSE	Illustrate that air has mass and occupies volume
MATERIALS	two 2-liter plastic soda bottles water tornado tube
PROCEDURE	Completely fill a 2-liter plastic soda bottle with water. Connect it with a tornado tube (found at your local toy store or science store) to another ``empty'' 2-liter bottle. Place it so that the water-filled bottle is on top.
DISCUSSION	With the water-filled bottle on top, the air can not enter from the bottom bottle and thus the water does not flow. If you swirl the apparatus, a vortex will result as air and water exchange places.
HAZARDS AND DISPOSAL	None.

N. THE MASON JAR

PURPOSE	To illustrate that the atmosphere has a mass and exerts pressure (atmospheric pressure).
MATERIALS	wire screen mason jar with cap water
PROCEDURE	Cut a fine wire screen to fit the interior section of the mason jar and screw the cap onto the jar. Fill with water and invert -- keeping it absolutely vertical.
DISCUSSION	The atmospheric pressure coupled with a surface tension effect prevents the water from flowing out.
HAZARDS AND DISPOSAL	None.

O. PING PONG BALLS AND AIR

PURPOSE	To illustrate that air has mass and the relationship between volume and pressure of a gas (Boyle's Law).
MATERIALS	One 2-liter plastic bottle One 1-liter plastic bottle ping pong ball (or cork) water
PROCEDURE	Cut the top off a 2-liter bottle and fill the bottom halfway with water. Add a ping pong ball or cork. Cut the bottom off of a 1-liter bottle and place the top (with cap on) over the ball in the 2-liter bottle. Push down on the 1-liter bottle. With the 1-liter bottle still pushed down, unscrew the cap. Try other possible positions. Replace cap with a one hole stopper fitted with a small tube so that you can adjust the amount of air being left out.
DISCUSSION	As you push the 1-liter bottle down, you increase the pressure within the system which causes the ball to sink. Lifting the 1-liter bottle relieves the pressure, allowing the ball to rise. Unscrewing the cap allows built-up pressure to be relieved.
HAZARDS AND DISPOSAL	None.

AUTHORS

Norma Ashburn, Ronald Blatchley, Bette Bridges, Stephen Danna, Greg Dodd, Jon Feeney, Enza McCauley, and Diane McGann.

Woodrow Wilson Leadership Program in Chemistry lpt@www.woodrow.org
The Woodrow Wilson National Fellowship Foundation webmaster@woodrow.org
CN 5281, Princeton NJ 08543-5281 Tel:(609)452-7007 Fax:(609)452-0066