Disinfection is a process of killing disease-causing organisms (or pathogens). Chlorine (Cl2) is a widely used disinfectant because, when mixed with pure water, it reacts to form hypochlorous acid (HOCl) and hydrochloric acid (HCl). HOCl (free active chlorine) is the most effective form of chlorine for disinfecting swimming pools, spas and drinking water.In some industries that work with drinking water, they add chlorine to the water supply as chlorine gas, liquid sodium hypochlorite, or dry calcium hypochlorite. In water, these form free chlorine ions, which destroy disease-causing pathogens, reduce odors, kill bacteria, and help remove unwanted elements. The USEPA (US Environmental Protection Agency) requires that residual disinfectant be present in final drinking water to ensure that disinfectant is available throughout the distribution system, and that chlorine acts as one of the disinfectants provided by said residue. However, the EPA (US Environmental Protection Agency) has also set a maximum contaminant level of 4.Main Features The HI3875 is a test kit that determines the concentration of free chlorine within a range of 0.0 to 3.5 mg / L (ppm). The HI3875 is supplied with all the necessary reagents and equipment to perform the analysis, including the Checker ® disc for an accurate determination. All necessary materials are included with the test kit, such as glass vials, plastic pipette, reagent packs, and Checker ® disc to perform approximately 100 tests. Readings from 0.0 to 3.5 mg / L are determined to 0.1 mg / L resolution It is not necessary to buy a new kit when the reagents are exhausted. The HI3875-100 reagent set can be ordered to replace the reagents supplied with the kit. This reagent set comes with 100 packs of HI93701-0 Free Chlorine Reagent and 1 bottle (500 ml) of deionized water. Each HI3875 Free Chlorine Kit is equipped with: - Free Chlorine Reagent HI 93701-0, packets (100 u.) - Deionized water, 1 bottle (500 ml) - 1 checker disc (contains the disc) - 2 glass vials with caps - 1 plastic pipette (3 ml).