ARCHIVED Questions and Answers
Sir Humphrey Davy [INDEX: Historical]
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Sir Humphrey Davy [INDEX: Historical] by Bill Stevenson
Posted: July 14, 1998 @ 00:39.
Date: Wed, May 27, 1998
Bill Stevenson wrote:
Are there any groups or members who specialize in gas lamp theory? I am interested in Sir Humphry Davy who is supposed to have discovered that a flame will not pass through a fine screen. He used steel screens and later silver plated ones to prevent rust. Somehow he was connected with lamps that burned the more volatile chemicals and there was a need to prevent gas lamps from exploding. I would think this would relate later to the Bunsen burner as well as the gas Thorium mantles on Coleman and Aladdin lamps. I would like to know what size mesh is this true for and what is the theory behind this.
Thanks in advance, Bill
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On July 14, 1998 @ 00:40, Fil Graff
wrote:
P> Guild ResponseBill: I'll post this on the Q&A page, but suspect Heinz Baumann <baumann@sc3101.med.buffalo.edu> or John Claypole <Lightinter@aol.com> will have some thoughts thereon!
Fil Graff, Secretary
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On July 14, 1998 @ 00:43, Heinz Baumann
wrote:
Date: Thu, 28 May 1998 13:01 EDT
Heinz wrote:
The gauze (or mesh) structure of an incandescent mantle (Aladdin, Coleman, or any others) is meant to be the carrier of rare earth oxides, and not to dissipate heat or to prevent passage of the flame. In contrast, the wire mesh often encountered on top of gas (e.g. "Bunsen burners") and fluid vapor (kerosene and alcohol) burners assist in the burning process, in part by adding surface area for combustion and distribution of the flame.
In 1815, Humphry Davy (see picture attached) studied the explosion process caused by methane gas (or "firedamp") commonly encountered in coal mines. He recognized that methane gas ignites at high temperature, e.g., at the temperature produced by open flame lamps. To prevent that heating to occur, he constructed a lamp with a two-layer metal gauze chimney. The principle function of the metal mesh is to dissipate the heat of the flame and thus to maintain a temperature outside of the lamp below a critical level. While it is correct that under normal burner settings the flame is confined within the gauze chimney, a passage of the flame through the wire mesh or heating to ignition point of gas outside of the chimney could in principle occur at extremely high setting of the flame within the lamp or at high air draft condition. The Davy lamp also indicates the presence of methane in the air. By drawing methane-containing air into the Davy lamp, the flame become larger (extended). Hence, the change in flame size serves as marker for the presence of significant amounts of combustible gas.
Heinz Baumann