a white powder that decomposes on contact with water and has the characteristic odor of gaseous chlorine: regarded, when dry, as a mixed calcium hypochlorite-chloride, used as a commercial bleach for wood pulp, textiles, oils, and soaps, and in laundering as a decolorizer and disinfectant.
Also could contain peroxides such as hydrogen peroxide, or hypochlorites, such as bleaching powder.
Treatment with acids followed by bleaching powder has been recommended for decomposition.
British Dictionary definitions for bleaching powder
a white powder with the odour of chlorine, consisting of chlorinated calcium hydroxide with an approximate formula CaCl(OCl).4H2O. It is used in solution as a bleaching agent and disinfectant Also called chloride of lime, chlorinated lime