Demonstration dips his wettened fingers into molten lead

[thenewbosco]

Just reading a textbook and came across this interesting question:

"a daring lab instructor in a demonstration dips his wettened fingers into molten lead (327C) and withdraws them quickly without getting burned. How is this possible?"

I was thinking simply that the water on the fingers will absorb the heat and since he withdraws his fingers quickly it won't reach his hand but this sounds a little shady...any other ideas on this?

 

[ranger]

The water vaporizes to form a protective sheath.

QUESTION: The professor readies a pan of molten lead, measuring 740 F. on the industrial thermometer, then prepares to plunge in a finger. What's he trying to prove?

ANSWER: It's Jearl Walker of Cleveland State University doing another wacky physics demo, described in "Fundamentals of Physics Extended, 5th Ed." He had read of 19th century carnival showmen dipping wet fingers into molten lead, and figured he was on to their secret: "As soon as the performer's wet flesh touched the hot liquid metal, part of the water vaporized, coating the fingers with a vapor layer. If the dip was brief, the flesh would not be heated significantly."

So Walker wetted a finger and took the plunge. "Amazingly, I felt no heat." The water had indeed vaporized to form a pro tective sheath. Growing bolder, he wetted and dipped in all the fingers of one hand, deep enough to touch the pan bottom.

"Still I questioned my explanation. Could I possibly touch the lead with a dry finger without suffering a burn? Leaving aside all rational thought, I tried it, immediately realizing my folly when pain raced through the finger." Then he dipped in a dry wiener, which blackened within seconds, lacking also the vapor protection.

NEVER, NEVER try this, warns Walker. A slight mistake can cause lead to solidify around the fingers, or send searing splashes onto the body. "I have been scarred on my arms and face from explosive vaporizations."

 

[FredGarvin]

The cold water absorbs the heat before the fingers do. It only lasts a very brief time. Dessert chefs do something very similar when making various candies. They test what stage their molten sugar is at (softball, hardball, soft crack hard crack etc...)by dipping their hands in water and then grabbing a small portion of the molten sugar with their two fingers. They immediately take the molten sugar and put it under the water again to get the feel for the sugar. It doesn't burn you even though the molten sugar is usually well over 300 degrees.