In the manufacture of ammonium sulphate, whether by using evaporators or saturators, the erosive effect of crystals present in solution, the low sulphuric acid concentrations usually present, and the relatively high temperatures of operation give rise to serious corrosion problems which begin at the drawing board stage of design and continue through all stages of manufacture. These corrosion problems are discussed in detail in this article and advice is given on materials of construction, including stainless steels, nickel alloys, rubber‐lined mild steel, lead, silicon irons, aluminium and a number of plastics.