Sentence:  With weld and cochineal, which are colouring matters the most sensible to the action of sulphate of iron, the purified <WSD>alums</WSD> gave us colours more brilliant, fresh, and in a slight degree lighter; while those with our common <WSD>alums</WSD> were all duller, and evidently of a deeper hue. 
Meaning of the word marked with <WSD> tags:  Any similar double sulphate in which either or both of the potassium and aluminium is wholly or partly replaced by other univalent or tervalent cations. (from 17th c.)