Which one of the following methods is used for the estimation of chlorine demand of water?

Chlorine demand of water : Is the amount of chlorine that is needed to destroy bacteria, and to oxidize all the organic matter amd ammoniacal substances present in water. Is the amount of chlorine added to water minus amount of residual chlorine remaining at the end of a specific period of contact (1 hr). Estimation of chlorine demand of water (or dose of bleaching powder required for disinfection of water) is done by ‘Horrock’s apparatus.