Acetic acid 99%, also known as glacial acetic acid, is a colorless, strong organic acid that is liquid at room temperature. Its correct melting temperature is actually 16.6 °C. At temperatures below this value, the acid crystallizes and assumes a solid form, giving it the name glacial acetic acid.

Glacial acetic acid is used in many industrial and laboratory applications, including the manufacture of plastics, pharmaceuticals, and dyes. In histology and cytology, it is often used as a component in staining solutions.

Although acetic acid in dilute form is a common ingredient in food and household products, glacial acetic acid can be hazardous due to its high concentration. It is corrosive and can cause severe skin and eye irritation on contact.

It is important that acetic acid 99% is handled only by trained professionals and used in a well-ventilated environment with proper protective equipment. Despite these risks, glacial acetic acid is an important reagent in many areas of science and technology due to its chemical properties and versatility.