Bleaching powder is made by the reaction of chlorine and calcium hydroxide (hydrated lime). Because absolutely dry calcium hydroxide does not react with chlorine gas, chlorine gas can only be adsorbed by calcium hydroxide. Therefore, in industry, hydrated lime with free water content less than 1% is used for chlorination, and the chlorine used also contains less than 0.06% water. Using the free water in these raw materials, chlorine gas is hydrolyzed to generate acids (HClO, HCl), and the generated acids are neutralized with hydrated lime. Subsequently, when chlorine is chlorinated, the water separated from calcium hydroxide continues to hydrolyze, which makes more calcium hydroxide participate in the reaction process and generates a series of compounds.
As a disinfectant, bleaching powder is safe for human body when used correctly. But bleaching powder has bleaching effect, and its appearance is similar to that of flour. If mixed with flour, it is difficult to identify. Therefore, some unscrupulous traders illegally use bleaching powder in food, such as bleaching flour, mushrooms and other foods with bleaching powder. Eating flour bleached with bleaching powder can cause food poisoning.
Bleaching powder aqueous solution can stimulate and corrode gastrointestinal mucosa. Chlorine, the decomposition product, is a highly corrosive and toxic gas, which can irritate respiratory tract and skin, cause cough and affect vision. Except for drinking the concentrated bleaching powder directly, no problems were found in the case of using its dilute solution. If the concentration is high, it is easy to feel the smell of chlorine and control it.