Ferric Chloride, commonly known as Iron (III) chloride and Iron chloride, is a commodity chemical product used in industry. When the chemical is dissolved in water, it undergoes hydrolysis, culminating in a dark, extremely corrosive, acidic solution that is employed as a flocculent in sewage treatment and the generation of drinking water. Anhydrous iron (III) chloride is a strong Lewis acid used in chemical synthesis as a catalyst. Ferric chloride is a hygroscopic crystal in its natural state. Its hue changes depending on how you look at it. The crystals appear dark green in the reflected light.