Aluminum sulfate is known by a variety of names, among them cake alum and filter alum. This latter name refers to its use in water treatment. It is found in anhydrous form near volcanoes and in the waste dumps at coal mines.
The molecular formula for cake alum is composed of two aluminum atoms and three sulfate (SO4) molecules. At room temperature, it usually looks like a white crystalline solid. The melting point for this compound is 770 degrees Celsius.
The primary usage for filter alum is in water filtration. Particles of the compound function excellently as flocculating agents. The impurities coagulate around it and become much easier to remove when the formerly suspended particles settle to the bottom of the container.
This compound also works as a mordant for the textile industry. Its proper application helps dyes to attach to fabrics. There are other products on the market which also include cake alum, such as antiperspirants.
Note: Seidler provides both aluminum sulfate 50% liquid and aluminum sulfate 50% dry.