Here's why:

* Element: A pure substance that cannot be broken down into simpler substances by chemical means. Sulfur is found on the periodic table, indicating it's an element.

* Compound: A substance formed when two or more different elements are chemically bonded together. Brimstone itself is not a compound, but rather a specific form of elemental sulfur.

Therefore, brimstone is just a name for sulfur, which is an element.