The place was Edinburgh, Scotland. The occasion, the Edinburgh Science Festival. There were a number of captivating presentations, but my biggest thrill came from looking out the hotel window. A light rail track was being constructed just outside and the workers were busy welding. My eyes popped when I saw what they were doing. I was looking at a live thermite reaction! I had talked about this reaction in class on numerous occasions and marvelled on it in videos, but had always deemed it too dangerous to perform.
A chemical reaction that produces heat is said to be “exothermic.” The most common example would be the combustion of a fuel. Light a candle and you can feel the heat that is produced. The hottest part of a flame, where the colour is a light blue, can reach a temperature of about 1400 degrees Celsius. But that is a low temperature compared to the 2500 degrees produced by the “thermite” reaction between aluminum and iron oxide. Essentially, this reaction involves the transfer of oxygen from the iron oxide to aluminum to yield aluminum oxide and metallic iron. At this high temperature, the iron is in its molten form and sets fire to any combustible material in its path, making the thermite reaction ideal for use not only in welding, but also in incendiary bombs and grenades.
Back in 1893, German chemist Hans Goldschmidt was looking for a way to produce pure metals from their ores. The classic method for extracting iron relies on heating iron oxide ore with carbon. The carbon is converted to carbon dioxide as it strips oxygen from the iron, leaving behind metallic iron. Some unreacted carbon, however, tends to contaminate the iron. Goldschmidt was looking for a way to produce iron without the use of carbon and hit upon the reaction of iron oxide with aluminum. He was impressed by the remarkable amount of heat produced and suggested that the reaction he had discovered could be used for welding. In 1899, the thermite reaction was put to a commercial use for the first time, welding tram tracks in the city of Essen.
It didn’t take long for the military to realize the potential of this extreme exothermic reaction in warfare. In 1915, the Germans terrorized England by using Zeppelins to drop incendiary bombs based on the thermite reaction. By the Second World War, the battle was on not only between Allied and German armed forces, but also between their scientists and engineers who sought to produce more effective incendiary devices. The Germans came up with the “Elektron” bomb, named after Elektron, an alloy composed of 86 per cent magnesium, 13 per cent aluminum and 1 per cent copper that was used for the casing of the bomb.
This alloy burns with a very hot flame, but requires a high temperature for ignition. The thermite reaction was up to the task. When an Elektron bomb hit the ground, a small percussion charge of gunpowder ignited a priming mixture of finely powdered magnesium and barium peroxide. This reaction produced the heat needed to ignite the thermite mix of aluminum and iron oxide, which in turn ignited the highly combustible casing. The Allies developed similar types of bombs resulting in the most destructive air raid in history, which was not Hiroshima or Nagasaki, but the firebomb raid on Tokyo in March 1945. An Allied bombing of Dresden the same year with incendiary bombs virtually destroyed the whole city. During the Second World War, the Allies dropped some 30 million 4-pound thermite bombs on Germany and another 10 million on Japan.
Thermite hand grenades were also used during the war to disable artillery pieces without the need for an explosive charge, very useful when silence was necessary to an operation. This involved inserting a thermite grenade into the breech of a weapon and then quickly closing it. The great heat produced by the thermite reaction welded the breech shut and made loading the weapon impossible. Alternatively, a thermite grenade was discharged inside the barrel of an artillery piece making it useless.
During the Vietnam war, thermite grenades found a different use. From the start of hostilities, putting a crimp into the enemy’s food supply was part of the U.S. military strategy. Since rice was a staple for the Viet Cong, destroying rice paddies was a primary goal. At first, attempts were made to blow up rice stocks and destroy paddies with hand grenades and mortars, but this proved to be maddeningly difficult. The next idea was to burn the rice paddies with thermite grenades. All this did was scatter the rice grains, which could then still be harvested. Another approach was needed.
Enter “Agent Blue,” an arsenic-based herbicide, unrelated chemically to the more infamous Agent Orange. Agent Blue affects plants by causing them to dry out, and as rice is highly dependent on water, spraying Agent Blue on rice paddies can destroy an entire field and leave it unsuitable for further planting. The U.S. used some 20 million gallons of Agent Blue during the Vietnam war, destroying thousands of acres of agricultural fields and defoliating wooded areas that the Viet Cong used to ambush American troops.
Recently, the thermite reaction made the news in a different context. Conspiracy theorists purport that it was thermite explosives planted inside the World Trade Center that brought down the twin towers in a CIA coordinated plot. They also maintain that the moon landing was faked and that the U.S. government is hiding the bodies of aliens. Some also claim that the rise of Donald Trump was engineered by a Democratic conspiracy and that on the verge of being elected he will announce “fooled you.” Wouldn’t that be something? It would trump the thermite reaction for heat generated.
Dr. Joe Schwarcz
If you’re on medications you might just want to skip the grapefruit with breakfast. Compounds in grapefruit inhibit enzymes (namely SYP3A4) in the small intestine that work to metabolize drugs. Without action of this enzyme, more of a drug is absorbed into the blood stream instead of being broken down, which can lead to an overdose. Other compounds found in grapefruit can inhibit drug transporters, which would normally help to absorb drugs into the bloodstream, leading to reduced doses of medications. These compounds are also found in Seville oranges (the oranges usually used for marmalade) and tangelos, so be sure to ask your doctor about the safety of your next citrus snack!
Pick an apple off a tree, buff it a little and it will shine! That’s because the fruit is coated with a layer of natural wax that protects it from drying out and helps to prevent fungi from getting a foothold. The wax is a mixture of up to fifty different compounds, most of which fall into the chemical category known as esters. There are also alcohols like heptacosanol and malol as well as hydrocarbons such as triacontane, C30H62. This compound can also be isolated from petroleum and is sometimes applied to fruit to supplement its natural wax. In that case chemophobes kick and scream about a petroleum derivative being applied to their fruit but there is no difference between triacontane produced by an apple isolated from petroleum.
Natural wax also contains compounds in the triterpenoid family. Ursolic acid has a variety of biochemical effects that have been demonstrated in laboratory experiments. For example, it can inhibit the proliferation of various cancer cells and also has weak aromatase inhibitor activity. Aromatase is an enzyme that leads to the synthesis of estradiol, the body’s main estrogen that is implicated in some cancers. This of course does not mean that the amount of ursolic acid in the peel of an apple can have a beneficial effect on human health, but it is at least another plus for eating apples.
After apples are picked they are washed before they appear in the supermarket to remove dirt and chemical residues. This process also removes the wax. Since the waxy layer prevents moisture in the apple from escaping, its loss shortens the storage time for the fruit. Producers therefore spray the fruit with a thin layer of wax to prevent such moisture loss as well as to make the apple look more appealing. The applied layer is very thin, only about 3 mg of wax coat an apple.
Several different types of wax are used, mostly Carnauba wax that comes from the leaves of the Brazilian palm, Candelia wax from a dessert plant, as well as food grade shellac from the Indian lac bug. There are also some synthetic esters made by combining sucrose with fatty acids. Polyethylene, the same plastic used to make disposable shopping bags can also be applied in a very thin layer. Interestingly, this can be termed as being vegan because it is made from ethylene which in turn is made from ethanol that is produced by the fermentation of corn. A trace of an emulsifier morpholine oleate is added to allow the wax to be spread in a thin layer. Some concerns have been raised that the wax seals in pesticide residues that cannot be removed by washing but studies have shown that the prior washing removes most traces of pesticide residues. As far as the wax itself goes, it presents no health issue since it is not absorbed and passes right through the digestive system. Wax coatings can also be used on organic produce with the proviso that they must come from a natural source like beeswax or Carnauba wax or wood resin. While there is no worry about eating the wax on fruits, they should be well washed mostly to remove bacteria that may have stuck to the surface.
A video has been circulating in which boiling water is poured over an apple resulting in the formation of white splotches as a voice drones on warning people not to eat waxed apples because of the pesticide residues. The message is that the boiling water reveals the pesticide residues. That is not the case. The heat cracks the wax coating allowing air to enter between the wax and the skin of the apple resulting in white patches due to the way the air pockets reflect light.
It is not just apples that are waxed. Citrus fruits, rutabagas, cucumbers, many tomatoes, melons and peppers also are treated with wax. Even jellybeans are coated with beeswax to prevent them from drying out and to increase their appeal.