This paper reports the effectiveness of (a) sodium sulphate, (b) sodium phosphate and other inorganic compounds, and (c) a number of organic materials in protecting steel against intercrystalline attack. The test results, given in the tables, form the basis for concluding that certain materials are effective in protecting steel against such attack; from the least effective to the most effective these chemicals would be (1) sodium carbonate, (2) sodium phosphate, (3) sodium sulphate, (4) quebracho and Philippine cutch, (5) lignin sulphonate, and (6) concentrated sulphite waste liquor. The position of sodium sulphate and other inorganic salts in this list is determined by their action in solution rather than any possible mechanical plugging they may cause.