Which one of the following method is used for the estimation of the chlorine demand of water -

Horrock's apparatus is designed to find out the dose of bleaching powder required for disinfection of water. The indicator used is starch iodide solution. Though chlorometer is the instrument used to find the amount of chlorine in the given solution, chlorine demand is best identified by Horrock's. Park's Textbook of Preventive and Social Medicine, 25th edition, Page No. 788,776