1) Lactic acid, also called 2-hydroxy prop ionic acid, C3H6O3 in molecular formula, CH3CHOHCOOH in structural formula, 90.08 at molecular weight, is a kind of natural organic acid and one of the main compositions of yoghourt, which exists in the blood and muscle tissue of the human body and animal.

2) At the room temperature, the lactic acid is a kind of colorless or yellowish and slightly sour liquid. Its crystal is low at the melting point, soluble in water and organic solvents dissolved in water (such as ethanol, ether), but insoluble in most of other organic solvents.