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A solution of sodium hypochlorite is sometimes used for bleaching purposes instead of bleaching powder, and then contains 1 to 2 per cent, of NaOCl. By cooling a concentrated solution, from which sodium chloride has deposited, to -10°, and shaking, crystals of NaOCl,6H2O, or NaOCl,7H2O, separate. These are very deliquescent, and melt at 18°. On cooling the fused substance, large crystals of NaOCl,5H2O are formed.
Calcium hypochlorite, Ca(OCl)2, is prepared in crystals by passing chlorine into milk of lime, and evaporating the clear solution in vacuo. The crystalline hydrate, Ca(OCl)2,4H2O, is first deposited on evaporation. The commercial product (maxochlor) is more stable than bleaching powder, is completely soluble in water, and contains about 74 per cent, available chlorine (theoretical hypochlorite oxygen in Ca(OCl)2 = 22.4 per cent., hence equivalent of Cl = 22.4 x 71/16 = 99.5 per cent.).
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