Calcium chloride is a colorless or white solid that is produced as a by-product of the manufacture of sodium carbonate or from reactions between hydrochloric acid and calcium carbonate. The anhydrous compound is commonly used as a drying agent, absorbing water until it dissolves into a liquid. This characteristic makes it effective in settling road dust. When spread in the form of a powder or flakes, it absorbs more than its own weight of water, forming a liquid that keeps the road wet. It also is used as a food preservative, treating aquarium water, and for de-icing roads.