The Chemical History of a Candle · Lecture III, part 2 · Part 3: Lecture III: Water and hydrogen
8. Iron, steam, and a gas that burns
Goal: Your child can explain that the water from a candle comes partly from the candle and partly from the air, and describe how iron took something out of steam.
You'll need
- A plain iron nail or a pad of plain steel wool (no soap)
- A saucer with a little water
- Science notebook
What's in the book
Faraday asks where the candle's water comes from. He shows potassium, iron and zinc acting on water, passes steam over red-hot iron in a gun-barrel, collects a gas that burns, pours it upward from jar to jar, and makes the same gas with zinc and acid.
The lesson, step by step
Hook question
SayThe water from the candle has to come from somewhere. Is it hiding inside the wax? Is it in the air?
Read together
Read pages 81 to 90, stopping at "This is hydrogen."
Water is the same everywhere, whether produced from the ocean or from the flame of the candle.
Faraday's answer
It is neither in one nor the other, but it comes from their conjoint action, a part from the candle, a part from the air
SaySomething from the wax and something from the air join together in the flame and make brand-new water.
Start a slow experiment: iron and water
Faraday says iron filings in water "become rusty" and act on the water slowly, much more gently than potassium does. Put the nail or a little steel wool on a saucer with a few spoonfuls of water. Look at it every day this week and note the rust in the notebook.
What Faraday did
Watch only: don't try this at home.
Faraday packed an iron tube with iron turnings, made it red-hot in a furnace, and passed steam through it. What came out was not steam: it did not turn back into water when cooled, and it burned with a little noise.
Steam puts out a fire — it does not burn; but you saw that what I had in that jar burnt.
The iron came out heavier, because it had taken something out of the steam. The new gas was so light that he could pour it upward from one upside-down jar into another. He also made it from zinc and acid. Red-hot furnaces, acids and burnable gas are laboratory work. If you want to see it, search online for a video of a chemistry teacher doing this demonstration and watch it together.
Say it back and check
Narration prompts: What did the steam do to the hot iron? How could Faraday tell the gas was not steam? How did he pour a gas upward?
Check questions:
1. Where does the water from a candle come from?
2. Why did the iron get heavier?
3. Why do you think Faraday held the jars upside down?
What we know now
Rust is iron joined with oxygen (with water helping). In Faraday's hot tube, the iron took the oxygen out of the steam and let the hydrogen go, which is why the iron got heavier.
Afterwards
Notice it this week: check the nail or steel wool each day. Rust is iron slowly doing what the red-hot iron did quickly.
Tip
You will meet the name of the light gas at the start of the next lesson. If your child guesses it, wonderful.
Answers to the book's problems
1. Partly from the candle and partly from the air; it is made by the two acting together in the flame. 2. It took something out of the steam (we now know it was oxygen) and kept it. 3. Because the gas is very light: it rises, so an upside-down jar keeps it in.
Worked out for this site from the scan. If a number in your copy differs, trust the book.