The 1827 Christmas Lectures
of Michael Faraday

Lecture #2

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.

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.

WEIGHT

Exp. 12: Hand glass-Bladder glass-Fixed jar

We are unable to figure out what Faraday was trying to demonstrate with this experiment.

ELASTICITY

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

Obscure.

EXPANSION

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.

COMBUSTION

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.

OXYGEN

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.

NITROGEN

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.

EDITORS

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
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