Presumably you mean sulphate of potash, not sulphur... If so, this is useful for scattering on the ground at the base of fruiting/flowering plants - at the right time of year, which depends on the plant. If it looks really old, I'd dispose of it though.

Potash is used by the plant for expansion of new parts, including flowers, fruit, or roots, and it is involved in disease and pest resistance. Sulphate of potash is a particularly strong form of this nutrient, and is slightly acid forming, so it should be used with caution, especially if it has become lumpy from exposure to water. With that caveat, it is especially good for fruit-bearing and root veggies, such as tomatoes, peppers, squash and melons, onions, beetroot, radishes, and turnips. It is also good for flowers and flowering shrubs of tropical derivation, such as petunias, hibiscus, and Solanum, and (as in the root veggies) flowering bulbs.