bleaching powder, white or nearly white powder that is usually a mixture of calcium chloride hypochlorite, CaCl(OCl); calcium hypochlorite, Ca(OCl)₂; and calcium chloride, CaCl₂. Sometimes called chloride of lime, it can be prepared by reacting calcium hydroxide or slaked lime, Ca(OH)₂, with chlorine gas, Cl₂. It is used as a strong bleaching agent, as a disinfectant, and in making Javelle water. Bleaching powder was first produced in 1799 by Charles Tennant in Glasgow, Scotland.