Which of teh following is not true regarding bleaching powder-

CHEMICAL DISINFECTION (1) Bleaching powder: Bleaching powder or chlorinated lime (Ca0Cl2 ) is a white amorphous powder with a pungent smell of chlorine. When freshly made, it contains about 33 per cent of "available chlorine". It is, however, an unstable compound. On exposure to air, light and moisture, it rapidly loses its chlorine content. But when mixed with excess of lime, it retains its strength; this is called "stabilized bleach." Bleaching powder should be stored in a dark, cool, dry place in a closed container that is resistant to corrosion. The chlorine content of bleaching powder stocks should be frequently checked. The principle in chlorination is to ensure a "free" residual chlorine of 0.5 mg/litre at the end of one hour contact. Highly polluted and turbid waters are not suited for direct chlorination Ref: Park 25th edition Pgno : 753