Washing of Crystals and Precipitates: When sodium or potassium hydroxide forms carbonates by absorbing carbon dioxide from the air or when there are precipitates of copper or iron hydroxides, they can be soaked in water for several days, then washed with dilute acid to convert them into water-soluble substances, and finally rinsed with water. If organic matter precipitates are present, they can be washed with boiling organic solvents or sodium hydroxide solutions. Washing of Amalgams: Mercury amalgams, which are alloys of mercury with some metals and leave dark stains on glass walls, can be dissolved with a 10% nitric acid solution, then rinsed with water. Washing of Dry Oils, Fats, and Paints: They can be washed with ammonia water; soft fats can be washed with organic solvents; kerosene can be washed with hot soapy water; sticky oils can be soaked and washed with hot sodium hydroxide solutions. Washing of Stains: White stains on glass, formed by long-term storage of alkali and腐蚀, can be cleaned with a solution of sodium bicarbonate or sodium hydroxide; yellow-brown rust stains on glass can be cleaned with hydrochloric acid solution; precipitates formed during the electrolysis of lead acetate can be cleaned with acetic acid; brown manganese dioxide spots can be cleaned with ferrous sulfate, hydrochloric acid, or oxalic acid solutions; ink stains on glass can be cleaned with sodium bicarbonate or sodium hydroxide solutions. Washing of Silver Salt Stains: Silver chloride and bromide stains can be cleaned with sodium thiosulfate solution; silver mirrors can be cleaned by dissolving them with a hot solution of dilute nitric acid to form easily soluble silver nitrate.