Before disinfecting a small rural water supply, a health officer needs to determine how much bleaching powder is required to achieve satisfactory chlorination. Which simple apparatus is specifically designed to estimate the chlorine demand of water in the field?

• A Orthotolidine comparator disc
• B Berkefeld filter
• C Jacketed fermenter
• D Horrock's apparatus ✓

Explanation

Horrock's apparatus consists of black porcelain cups used to find the chlorine demand of water by adding graded doses of bleaching powder solution and testing each cup after contact time; the lowest dose leaving a satisfactory free residual chlorine is chosen. The Berkefeld filter is a candle filter for purification, the fermenter relates to BOD work, and the OT comparator merely measures existing residual chlorine without determining the dose required. Chlorine demand equals applied dose minus residual chlorine.

Reference: Park's Textbook of Preventive and Social Medicine, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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