20:11 · A sign in early chemistry for water. In Dalton's chemical sign system from the beginning of the nineteenth century, was the sign for oxygen, while stood for hydrogen. Water is a compound of the elements oxygen and hydrogen. In the earliest chemistry, i.e. alchemy, water as a substance was represented by , , and . As one of the four elements water was often represented by the empty circle in the Middle Ages. In other contexts, not directly related to chemistry, water could appear as , , , and .
    Compare with , , and , and other signs for different types of rain.