The thick liquid used to be called "oil of vitriol," since it was originally made by the distillation of "green vitriol," or iron sulfate as we know it today. It was so corrosive and nasty that the term "vitriolic" entered our vocabulary to describe language that was particularly disagreeable.
Sulfuric acid is the substance that, in movies at least, sizzles through metal, burns skin and dissolves corpses. Although in real life it is not quite as deadly as in works of fiction, it is bad enough. We sometimes use it as a drain cleaner to dissolve all the accumulated guck which includes items ranging from hair to toothpaste tube caps. There is an important point worth noting about using concentrated sulfuric acid as a drain cleaner. It must never be mixed with any of the other commonly available drain cleaners which are based on lye (sodium hydroxide). Combining these two generates a tremendous amount of heat, enough to melt plastic pipes, as well as toxic acid vapors!
So if sulfuric acid is so dangerous, why are their tankers and trains criss-crossing the continent loaded with this liquid? The reason is actually simple. Sulfuric acid is the world's most important industrial chemical! In North America we produce about 50 million tons a year, mostly by burning sulfur to form sulfur dioxide which is then reacted with water. Why do we need all that sulfuric acid? Primarily to produce fertilizer. Sulfuric acid converts insoluble phosphate ore into a valuable fertilizer known as "superphosphate." Without this we could not even contemplate feeding the world. Then there are the detergents, the dyes, the drugs, the explosives, the paints, the metals and the car batteries, all of which require sulfuric acid for production.
Sulfuric acid also occurs in nature. Oil, coal and gasoline all contain small amounts of naturally occurring sulfur compounds. When these burn, their sulfur content is released as sulfur dioxide, a gas that eventually combines with moisture to form sulfuric acid. Presto, we have acid rain! In some areas the rain can be acidic enough to corrode limestone used in building construction. Limestone is calcium carbonate and reacts with sulfuric acid to form carbon dioxide and calcium sulfate that is washed away.
Many years ago during a lecture on acid rain I decided to demonstrate its effects by opening a bottle of the acid and hanging a nylon stocking nearby. The acid vapours soon formed large holes in the stocking. The students were impressed and undoubtedly learned something about acid rain. But I learned something too. I learned about the popularity of nylon underwear! The next day I was confronted by a couple of students who had gone home at night and discovered holes in their finery. Apparently the sulfuric acid vapours had a more wide ranging effect than I had expected. There was some explaining to do in the face of some pretty vitriolic language.
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