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Iron(III) chloride, generically called ferric chloride, is an industrial scale commodity chemical compound, with the formula FeCl3…When dissolved in water, iron(III) chloride undergoes hydrolysis and gives off heat in an exothermic reaction. The resulting brown, acidic, and corrosive solution is used as a coagulant in sewage treatment and drinking water production, and as an etchant for copper-based metals in printed circuit boards. Anhydrous iron(III) chloride is a fairly strong Lewis acid, and it is used as a catalyst in organic synthesis…
The above quote is from the Wikipedia entry for Ferric Chloride.
Joseph Beuys in the Speck Collection
Speck Collection, courtesy Gagosian Gallery