<prompt> Horroks apparatus determines Chloride which has to have a holding level of -0.1 mgL1 mgL0.01 mg0.5 mgL  <response>: Ans. is d i.e., 0.5 mgL Horrocks apparatus is used to find out the dose of bleaching powder required for disinfection of water by chlorination. o The principle in chlorination is to ensure a free residual chlorine o10.5 mglitre at the end of one hour contact. 