The Washington Monument's Apex

by Nate Burgess
Monday, October 26, 2015

An aluminum pinnacle has graced the Washington Monument since 1884, but subsequent modifications have changed the look of the point. In 1885, after the first major lightning strike to the monument, engineers were alarmed to find that the electricity had cracked a stone beneath the aluminum pyramid. They quickly outfitted the monument apex with a copper band and small lightning rods connected to a series of copper rods running down the corners of the stonework and connected to the internal lightning rods. In 1934, engineers discovered that the aluminum itself had deteriorated after years of lightning strikes. They replaced the copper band with eight larger copper rods extending 15.2 centimeters above the aluminum apex, hoping to shield the point from enough electricity to preserve the stone obelisk’s peak. So far, it has.

Alum, Alumina, Aluminium or Aluminum?

Though aluminum is the most abundant metal in Earth’s crust, comprising approximately 8 percent of the crust by weight, it rarely occurs in a pure form. Aluminum ions have a high affinity for oxygen, so when they are not bound within common minerals like feldspar, aluminum ions usually react with water and air to create aluminum oxides and hydroxides.

People throughout history have used these white powdery substances, but did not understand that they contained a metal. The Romans referred to the white powder as alumen, meaning a substance with a bitter, astringent taste. Ancient natural philosophers and alchemists conducted experiments with alumen, and the shortened word alum eventually came to refer to a chemical compound containing water, sulfur, potassium and aluminum.

In 1761, L.B.G. de Morveau suggested that alum was really a metal oxide and named the yet undiscovered base metal alumina. Subsequent 18th century scientists proved Morveau’s assertion and changed the name of the base metal first to aluminum and then to aluminium. Alumina now refers to aluminum oxide. The metal is still called aluminium in many parts of the world, though American chemists reverted to using the earlier name, aluminum, in 1925.

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