Lecture II - A Candle: Brightness of the Flame

Contents of this webpage

• Outline of Faraday's Chemical History of the Candle, Lecture II
• Reading Notes and Vocabulary for Lecture II
• Discussion Points to Think About Before Chat
• Related Websites (Optional Reading)

Outline of Faraday's Chemical History of the Candle, Lecture II

In this lecture, Faraday moves from the material in the candle to consider the nature of the candle flame, and the possibility that the flame produces something new from the candle material. Once he has show that candles combustion does result in new chemical products, by changing the air and candle wax into something else, he considers how other materials might burn to form different products as well. Then he returns to the problem of candle combustion: how do we identify the products, and what are their properties?

1. Combustion is the process of changing materials from one type of matter into another (chemical change)
2. The parts of the flame
   
   1. Dark area: production of the vaporous form of wax (demonstration shows this vapor burns when collected and ignited)
   2. Light area: vapor is consumed -- it becomes something else (so no vapor is available for collection)
   3. Location of the hottest part of the flame is around the center, not at the center
3. Air is necessary
   1. Demonstration with candle and oil: air required for any flame
   2. Partial combustion (resulting in smoke) occurs if not enough air is available
4. Types of combustion
   1. Can occur with flame (gunpowder)
   2. Can occur without flame (glowing embers of iron filaments)
   3. Multiple flames from lycopodium
5. Combustion products
   1. Soot (carbon) is produced in the "luminous part" of the flame
   2. Combustion of different materials produces different products
   3. Combustion of liquids and solids produces light (iron filings, platinum wire, lime)
   4. Combustion of gas does not produce much light--combustion of hydrogen gas produces water
   5. Combustion of solid carbon produces gas (carbon dioxide)
   6. Conclusion: flame production involves the combining of oxygen with some form of solid material
      1. Example: combustion of phosphorus produces gases and solids (as small particles in smoke)
      2. Example: combustion of zinc (philosophic wool)
      3. Example: burning camphine gives off carbon particles which can then be burned independently (producing flame)
      4. Example: adding air to the flame increases the heat so all the carbon is consumed in the initial burning
6. The products of candle combustion
   1. Large amount of some gas is produced (ascending balloon)
   2. Water is produced (vapor on side inside of glass tubing)

Reading notes

vaporous fluid:

Individual droplets suspended in air, as opposed to gas, which is individual molecules or atoms moving freely

fresh air:

Air which has not supported either combustion (flame burning) or respiration (lots of people breathing it); in either case, the oxygen is diminished.

Argand lamp:

See the diagram at the top of page 33. The main point is that the lamp is fed fresh air from the bottom directly into the center of the flame, which makes the flame much brighter than other lamps, and also provides for complete combustion (no smoke).

lycopodium:

Powder made from the spore of certain club mosses and used for fireworks and other explosives.

Limelight:

Faraday's demonstration is based on the use of lime lanterns to produce an intense white light which was used to light stages. The light was extremely hot--and caused a lot of fires.

The practice gave rise to the phrase "in the lime light" -- meaning "at the center of attention."

Philosophic wool:

A form of zinc oxide as a white, fuzzy residue from burning zinc in pure oxygen.

Discussion points

• What is combustion? What is happening to the wax in the dark and light parts of the flame? How does chemical change differ from the physical change (solid->liquid->gas) which Faraday demonstrated in the first lecture?
• Why is the hottest part of the flame not at its center?
• Faraday says that "all these things"--by which he means the wicks and oil lamps that he is using for a demonstration--"are the same as candles, after all." What does he mean? How are generalizations like this important to the process of scientific thought?
• How does Faraday separate the products of combustion? What methods does he use to identify the products?

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