Friday, September 25, 2015

Lead

Lead is element number 82. The oldest pure lead, found in Turkey, was made by early smelters more than 8,000 years ago. Galena is the natural mineral form of lead(II) sulfide, the most important ore of lead and an important source of silver. Thanks to its low melting point, the lead can easily be separated out in an open fire.
It had a lot of uses. Ice cores in Greenland contain traces of lead dust from 2,000 years ago, carried on the wind from giant Roman smelters. One of the largest, located in Spain, was operated by tens of thousands of slaves. The metal was malleable and seemingly impervious to corrosion, and so - just like modern plastics - it became ubiquitous. It could line aqueducts and make water pipes - the word "plumber" derives from the Latin for lead, plumbum. It is flexible; you can cast it into thin sheets, solder it into pipes. 
Lead carbonate has provided a cheap, durable paint since ancient times. Known today as "flake white", it was prized by Old Masters such as Rembrandt because of the steadfastness of its colour and the beautiful contrasts it would bring to their oil portraits.
Glassmakers learned that adding in some lead oxide would yield glassware such as wine decanters that would glisten, because the lead refracted the light across a wider arc. The lead slowly dissolves out into the wine itself. The intriguing thing is that you get a compound that used to be known as 'the sugar of lead'." This compound, lead acetate, not only looks like sugar, it also has an intensely sweet flavor; the wine would gradually become sweeter.
But lead, of course, is also toxic.
Citizens of Ulm in Germany were plagued by agonising stomach cramps in the 1690s, called "Devon colic" after a similar 17th Century outbreak. Dr. George Baker, a century later, showed this was the result of lead, a component of the cider presses and in the form of lead shot which was used to clean them. The general symptoms of lead poisoning, or plumbism, include abdominal pain, confusion, headache, anemia, irritability, and in severe cases seizures, coma, and death.

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