Double salt and Potassium alum

Double salt noun - A solution of two simple salts that forms a single substance on crystallization.

Potassium alum and double salt are semantically related. In some cases you can replace phrase "Potassium alum" with "Double salt", this phrases are similar.

Potassium alum noun - A white crystalline double sulfate of aluminum: the potassium double sulfate of aluminum.

Double salt and potassium alum are semantically related. You can use "Double salt" instead a noun phrase "Potassium alum".