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Gas flames burn blue. (Vitaliy Pakhnyushchyy/Getty Images/Hemera)
Gas flames burn blue. (Vitaliy Pakhnyushchyy/Getty Images/Hemera)


Answering a truly burning question Add to ...

This week, Collected Wisdom gets all fired up over a really hot topic. Yellow or blue hot, you might say.

The question

“Why does natural gas – in my stove, for example – burn with a blue flame, whereas most other flames are yellow or red?” asks Ross Smith of Courtenay, B.C.

The answer

Yellow or orange flames get their colour from tiny soot particles that glow brightly at the surface of the flame, known as the flame front, writes William Hallett, a professor in the department of mechanical engineering at the University of Ottawa.

“Soot is produced when fuel is heated without being in contact with oxygen,” he writes. “This causes the fuel to decompose chemically into light gases and a carbon residue (soot).”

In a diffusion flame such as a candle flame, the fuel and air enter the process separately and mix only when they meet and react at the flame front, he says. “The interior of the flame contains fuel vapour, but no oxygen, allowing the fuel vapour to be heated and transformed into soot.” When the fuel reaches the flame front and encounters air, the soot glows, causing the yellow flame.

Blue flames, on the other hand, result from what is called premixed combustion, in which fuel and air are completely mixed before they come to the flame, as they are in a natural-gas stove. Soot cannot be produced in a premixed flame, Prof. Hallett says, because the fuel is already in contact with oxygen and does not have the chance to produce soot. The blue colour comes from chemicals produced during combustion.

“Most natural-gas burners in domestic stoves and furnaces use premixed burners,” he writes, hence the blue flames.

The question

A while back, Frank Durante of Edmonton said his son Gregory asked him how the video camera was set up on the moon’s surface to record Neil Armstrong’s historic step down the ladder of the lunar module.

The answer

“There are conspiracy theorists who believe the moon landings were faked,” writes Marc Sheckter of Saskatoon.

“I suppose they might invoke the existence of a TV camera already on the moon, before Neil Armstrong set foot there, as ‘evidence’ of the fakery.”

However, he says, the answer is that the camera was not on the moon’s surface, but was attached to the lunar module.

The moment was described by Andrew Chaikin in his book A Man on the Moon as follows: “[Armstrong] could not descend [the ladder] yet; the world was waiting to see the event. Armstrong pulled a D-ring on Eagle’s side and an equipment stowage tray lowered like a drawbridge. On it, a small TV camera began transmitting to Earth.”

Help wanted

Is there any evolutionary advantage to the riot of colours produced by our trees each fall? asks Graham Duncan of Mahone Bay, N.S.

Since enormous quantities of oil are being pumped out of the ground, why is the ground not collapsing or sinking? Paul Niedermayr of Belleville, Ont., wants to know.

Marilyn Hintsa of Toronto asks: Before an orchestra performs a piece of music, how do they determine the number of each type of instrument required?

Bruce Valpy of Yellowknife writes: “Why, on the vast majority of U.S. movies and television dramas, when characters hang up the phone, do they never say goodbye? Is it something they teach in film school?”

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