Compare colors developed with color obtained when standard salicylic acid solution (containing 1 mg salicylic acid in 50 ml H2O)
is similarly treated, using Nessler tubes or colorimeter. In either case, and especially with FeCl3. avoid excess reagent, although excess of 0.5 ml.2% ferric alum solution may be added to 50 ml. comparison solution of solution salicylic acid without negating results.