The 1827 Christmas Lectures
of Michael Faraday
Atmospheric Air and its Gases
In his second lecture, Faraday continues his lecture-demonstration pedagogy. He conveys to his audience that air and other fluids exist (Exp. 1), have weight (Exp. 2-6, 12), volume (Exp. 18-20), elasticity (Exp. 7-11, 13-15) and exert pressure (Exp. 16, 17).
Faraday also demonstrates simple ways of producing the individual gases found in air (Exp. 22-24) and proving by reaction that they are different gases, primarily oxygen (Exp. 25-30) and nitrogen (Exp. 31-34). He shows that air can be made by putting these gases in one container in the proper ratio (Exp. 35, 36) and then demonstrates how this air supports combustion (Exp. 37) and compares it to combustion in atmospheric air (Exp. 21). Faraday also shows the presence of water and carbonic acid (CO2) in air (Exp. 38-40). He believed that showing these properties and reactions is a better way of getting his audience to understand these concepts than by just telling them.
His one-concept demonstrations are simple with each one leading directly into the next. Faraday is a master at making connections between the properties of gases and the composition and behavior of the atmosphere. Notice in experiment seven how Faraday relates the visible elasticity of the spiral spring to the elasticity of air in a piston and then, in the subsequent experiment, adds weights to illustrate changes in pressure. It is this method of instruction which makes chemical concepts comprehensible for audiences of all ages.
For the corresponding modern demonstrations, click on the icons .
PROOF OF EXISTENCE OF AIR
- Exp. 1: Fan-open hand wafted
- Faraday is showing the movement of air to prove that it is a material substance.
WEIGHT OF AIR
- Exp. 2: Room full weighs 4500lb or above two tons
- Faraday refers to a table from lecture one.
- Exp. 3: Jar with stones, crystal clear water, and floating bulb
- A jar was filled with solids (stones), water, gases - filled floating bulb to show different densities.
- Exp. 4: Bulb in water- Balloon in air
- This shows that a balloon floating in air is analogous to a bulb floating in water.
- Exp. 5: Smoke in air
- Exp. 6: Bottle of alcoholic sol cochineal at bottom of large jar of water slightly ammoniacal
- An open bottle of red carmine indicator placed in a jar containing a slightly basic solution illustrates slow diffusion in liquid.
ELASTICITY OF AIR
- Exp. 7: Spiral spring
- By exerting force on the spring, the elasticity of the spring is shown.
- Exp. 8: Glass flask of air with small tight caoutchouc bag on the mouth
- In this experiment, Faraday shows that air takes up space and is elastic.
- Exp. 9: Syringe -- piston half way up
- This is a demonstration in which the elasticity of air is analogous to the elasticity of the spring in Exp. 7.
- Exp. 10: Spring with weight on and off
- This again shows the elasticity of the spring.
- Exp. 11: Syringe with air weight on and off
- This again makes the analogy of air to a spring.
- Exp. 12: Hand glass-Bladder glass-Fixed jar
- We are unable to figure out what Faraday was trying to demonstrate with this experiment.
- Exp. 13: Bladder of air under receiver
- A tied-off bladder of air under a bell jar expands as pressure is diminished. Reversible.
- Exp. 14: Jar of down (feathers)
- This shows that down and feathers, like the atmosphere, show no distinct ceiling.
- Exp. 15: Pop-gun
- Here Faraday is showing that by compressing air a force is created that can propel an object across the room.
BAROMETER AND PRESSURE
- Exp. 16: Fluids poured in
- A U-tube is partially filled with mercury. Liquids of different densities are poured into the two legs.
- Exp. 17: Syphon from barometer tube
- Exp. 18: Air thermometer-bladder
- An air thermometer is demonstrated.
- Exp. 19: Montgolfier's Balloon
- A hot air balloon is demonstrated.
- Exp. 20: Ascent of smoke -- of hot air
- Faraday is showing that hot air is less dense and thus will rise in the air.
- Exp. 21: Phosphorus in air jar over water
- The combustion of phosphorus in a limited supply of air is shown. Inertness of residual air shown by second attempted combustion.
ATMOSPHERE AND ITS GASES
- Exp. 22: Amalgam of lead and mercury shaken in bottle
- Faraday shows the formation of litharge.
- Exp. 23: Mercury boiled as in Lavoisier's experiment
- Mercuric oxide is formed. Caution: do not attempt this demonstration.
- Exp. 24: Oxide of mercury heated and decomposed
- The results of Exp. 23 are reversed. The two parts of air are separated. Caution: do not do this demonstration.
- Exp. 25: Striking differences of nitrogen and oxygen
- The differences between oxygen and nitrogen are examined.
- Exp. 26: Oxide of manganese in iron retort
- The decomposition of manganese dioxide produces oxygen.
- Exp. 27: Red lead and sulphuric acid to generate oxygen
- Faraday again was trying to show the presence of oxygen in the collected gas.
- Exp. 28: Taper indicates presence
- A smouldering taper reignites, showing that oxygen is present.
- Exp. 29: Chlorate in wide tube and lamp
- The heating of potassium chlorate produces oxygen.
- Exp. 30: Supports combustion wonderfully -- burning taper, phosphorus, and hot iron in jar of gas
- He is again showing how oxygen supports combustion.
- Exp. 31: Nitrogen prepared (is left after phosphorus has taken oxygen)
- Faraday shows that nitrogen is the other major constituent of air. Caution: see Exp. 21.
- Exp. 32: Bottles and jars of nitrogen
- : Nitrogen has no effect on indicator paper.
- Exp. 33: No apparent active properties
- Faraday uses a taper to illustrate lack of combustion.
- Exp. 34: Alcohol burning pour water in
- Faraday shows that water added to burning alcohol reduces the activity of alcohol.
COMPOSITION OF AIR (NITROGEN, OXYGEN, WATER, CARBONIC ACID)
- Exp. 35: Oxygen and nitrogen in jars
- Prepare oxygen (Exp. 26) and nitrogen (Exp. 30, 31)
- Exp. 36: Mix proportions & try the mixture
- Mix oxygen and nitrogen in 1:4 proportion in jar producing a gas indistinguishable from ordinary air.
- Exp. 37: Cold vessel of water
- Water from air condenses on outside of vessel containing ice-cold water.
- Exp. 39: Drying of damp cloth over time
- This shows how water gets into the air -- evaporation.
- Exp. 40: Sub acetate of lead solution and burning candle under glass
- This reaction of lead hydroxy acetate with carbon dioxide forms lead carbonate and acetic acid -- The lead carbonate gives a turbidity to the solution.
Go to the modern lab demonstrations .
Norma Ashburn, Ronald Blatchley, Bette Bridges, Stephen Danna, Greg Dodd, Jon Feeney, Enza McCauley, and Diane McGann.
Woodrow Wilson Leadership Program in Chemistry
The Woodrow Wilson National Fellowship Foundation
CN 5281, Princeton NJ 08543-5281