The Leidenfrost effect explains a cool trick where a wet hand can be briefly dipped into molten lead without injury.
“Bertie,” as Queen Victoria and Prince Albert’s eldest son was known to the family, was not a stellar student, much to dismay of his parents. They tried to groom the Prince of Wales for his future role as King by sending him on tours of educational institutions hoping to spark a flame of interest. In 1859, the eighteen-year-old Bertie was introduced to Professor Lyon Playfair who was to be his guide for a tour of the chemistry labs at Edinburgh University. Playfair thought the prince would enjoy one of his favourite demonstrations and proceeded to pour some molten lead over the fingers of his assistant. Indeed, Bertie was amazed that the man’s hand was not scalded and asked if he could try the experiment. Professor Playfair instructed him to dip his hand in water, shake of the excess, and extend the royal fingers as he proceeded to pour the molten lead over them. The hand that would rule England as King Edward VII from 1901 to 1910 was unharmed. Young Bertie had learned about the Leidenfrost effect!
After graduating as a physician in 1741, Johann Gottlob Leidenfrost went on to teach medicine, physics and chemistry at the University of Duisburg in Germany. He published a number of scientific papers, including “a Tract About Some Qualities of Common Water” in which he described the effect that would be named after him. He had observed that droplets of a liquid placed on a surface considerably hotter than its boiling point skittered across the surface before turning into a gas instead of instantly evaporating. At a lower temperature, but still above the boiling point, the droplets immediately vaporized.
In a classic experiment, Leidenfrost placed a drop of water on a polished iron spoon heated over glowing coals and recorded that the drop “does not adhere to the spoon, as water is accustomed to do, when touching colder iron.” Rather, it hovered over the spoon as a spherical globule for close to half a minute before evaporating. Upon placing a candle behind the drop, Leidenfrost observed that light passed between the spoon and the liquid revealing the presence of a thin layer of vapour on which the droplet floated. This effect is often put to a practical use by cooks wishing to know if their frying pan is hot enough before adding food. If the metal has been heated enough, a few droplets of water sprinkled over the surface will skitter about before evaporating while a lower temperature will result in the water turning into steam as soon as it touches the pan.
The molten lead “trick” makes use of the same principle. Contact of water with the hot lead forms an insulating layer that prevents a burn. But as Adam and Jamie demonstrated on MythBusters, the molten lead has to reach a temperature of 450 C, some 120 degrees above lead’s boiling point, to prevent injury. They cleverly showed this by first testing on sausages instead of fingers before successfully plunging their digits into the molten lead. Thanks to the Leidenfrost effect, we have the curious phenomenon of a higher temperature causing less harm than a lower one.
The oldest lie-detector system in the world also relies on the same effect. In an ancient ritual used by Bedouin tribes, a member who professes innocence after being charged with a crime is given the chance to prove that he is not guilty. All he has to do is lick a red-hot spoon without blistering his tongue! The idea is that if he is guilty and nervous, his mouth will be dry and the tongue will burn as soon as it touches the hot metal. If he is innocent, there will be enough saliva in the mouth to offer protection via the Leidenfrost effect. This “trial by fire” is known as Bisha’h and has been banned by all governments in the Middle East except apparently Egypt where it is still performed. A good liar can probably muster up enough protective saliva, and I suspect there are some innocents who wish they had not agreed to lick the spoon.
It would be great to report that the dramatic demonstration of the Leidenfrost effect triggered an interest in chemistry for the Prince of Wales, but such was not the case. It seems the young man was more interested in debauchery. When his exasperated parents sent him to a military training camp in Ireland to correct his rambunctious behaviour, Bertie contrived to smuggle actress Nellie Clifden into his quarters to initiate him into manhood. When his mother the Queen heard about this, she sent her husband, Prince Albert to scold him. Albert reputedly told Bertie that “I knew that you were thoughtless and weak, but I could not think you depraved.” Albert died just two weeks after this chewing out of his son and Victoria blamed Bertie for precipitating the death by causing stress to his father. She never forgave him. “I never can, or shall, look at him without a shudder,” she said, and she never did.
Bertie was not totally disinterested in science. He was certainly interested in nutrition. Over-nutrition. He consumed gigantic meals and became, let’s just say, portly. His hunger, though, was not only for food. He had a spectacular appetite for sex! As time went on and his belly grew, he had a difficulty positioning himself and sought a scientific solution. He commissioned cabinet maker Louis Soubrier to create a special elaborately upholstered “Love Chair” that allowed him to perform without his enormous girth crushing his paramours. That chair still exists, as do some replicas that can be purchased for around $70,000. The “Siège d’Amour” was equipped with a second cushion that supposedly allowed for sex with two women at once. It seems there was at least one type of chemistry in which the future King Edward VII was interested.
Joe Schwarcz is director of McGill University’s Office for Science & Society (mcgill.ca/oss). He hosts The Dr. Joe Show on CJAD Radio 800 AM every Sunday from 3 to 4 p.m.
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