Double salt and Potash alum

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

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

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

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