Sulfur and its compounds have powerful uses for good and for evil.
In 1991 a volcanic eruption occurred on the island of Luzon, near the Philippines. In a short period of time Mount Pinatubo had injected into the atmosphere 10 billion tonnes of magma and 20 million tonnes of sulfur dioxide. In the months that followed, global temperature had fallen by 0.5 °C. The cooling occurred because of the formation of a thin layer of sulfuric acid that reflected the sun’s radiation.*
Apart from its rare use in cooling the atmosphere, sulfuric acid, a compound of the abundant element sulfur, is used in many industrial applications. So much so that the amount of the acid produced in a country could be a good measure of that country’s economic development. Sulfuric acid’s historical name is the oil of vitriol and the usage of the word vitriolic stems from its strongly acidic nature. When added to water (H2O) it forms sulfate ions in a heat-producing reaction. Such is its affinity to water that if added to sugar it removes hydrogen (H) and oxygen (O) from it leaving behind a tower of black carbon.
Sulfate ion is a doubly-negative ion that consists of a sulfur atom bonded to four oxygen atoms. Attached to some valuable elements, it is found in the form of minerals too. Gypsum, which is commonly used in plasters, is a sulfate salt of calcium. Another important ion of sulfur is the sulfide ion. Not unlike sulfates, sulfides are also found as minerals in sulfide metal ores.
But sulfide compounds are more commonly known for foul-smelling versions. Burning of sulfur results in the formation of hydrogen sulfide that smells like rotten eggs., which was once considered to be the “smell of hell”. This odd connection was probably the result of a similar reaction occurring near a volcano which, in the middle ages, was considered to be a gateway to hell.
Hydrogen sulfide is not half as bad as its cousin, dimethyl sulfide, which has a disagreeable odour even at low concentrations. And yet, dimethyl sulphide when diluted further is very important to our culinary experience. It is part of the smell of cheeses and the aroma of truffles.
Sulfur compounds have an evil side too. In World War I the Germans used mustard gas, a sulfide compound, that caused horrible blisters. Unlike chlorine, it was colourless and the effects of it were felt only after a few hours. Worse still, it did not kill but only incapacitated the soldiers.
Then there is sulfur hexafluoride, an utterly unreactive gas, that is used on an industrial scales to provide an inert atmosphere for reactions that occur over 1000 °C, for example in the smelting of magnesium. But sulphur hexafluoride is a greenhouse gas that has 32,000 times the potential of carbon dioxide. Even small amounts of the gas are very harmful to the planet, yet it is used on industrial scales. It seems, then, that sulfur and its compounds affect many things from the depths of hell to the very edge of the atmosphere.
* Many consider that mimicking this eruption to cool the planet may be necessary. But a British project, Stratospheric Particle Injection for Climate Engineering aimed to test the feasibility of such an intervention was cancelled in May 2012 because of patent issues and the lack of regulation over actions that can affect many nations.