Phase diagram--Hydrogen sulfide (H2S)

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Hydrogen sulfide is an inorganic compound; under normal conditions it is a colorless, flammable acidic gas. At low concentrations (0.13 ppm–4.6 ppm), it has an **egg-like odor**； At concentrations higher than 4.6 ppm, there is no odor (because high concentrations of hydrogen sulfide can numb the olfactory nerves). It is soluble in water; at 0 °C, 1 mole of water can dissolve 2.6 moles of hydrogen sulfide. An aqueous solution of hydrogen sulfide is called hydrosulfuric acid; it is a weak acid, and when heated, hydrogen sulfide escapes from the water. The solubility in water at 25°C is 4 mg/mL. The critical temperature is 100.2°C, and the critical pressure is 8.98 MPa. The hydrogen sulfide cylinders commonly used in laboratories are 8L (with a filling capacity of 5kg) and 40L (with a filling capacity of 30kg), with a purity of 99.9%.