The bread must be soaked in water, and to the water in which it has been soaked, a little of the solution of muriate of lime must be added, upon which, if any alum be present, the liquid will be pervaded with milkiness; but if the bread be pure the liquid will remain limpid. Rationale: sulphuric acid has a stronger affinity for lime than for the alumina and potass, with which it forms alum; it therefore quits those bodies to form sulphate of lime with the lime of the test, which produces the milkiness.