Horrok's apparatus determines Chloride which has to have a holding level of –
Horrock's apparatus is used to find out the dose of bleaching powder required for disinfection of water by chlorination.
The principle in chlorination is to ensure a free residual chlorine of 0.5 mg/litre at the end of one hour contact.
0.1 mg/L
1 mg/L
0.01mg /L
0.5 mg/L