So many papers on the use of the phenol disulphonic acid method for estimating nitrates in soils have been published in this country and in America in the last few years, that some apology seems needed for adding yet another note to the literature of the subject. The method possesses great advantages as regards rapidity and convenience over the methods involving distillation and yet in the writers' experience, in spite of the numerous studies already made, it has failed to give entirely satisfactory results; in particular when small quantities of nitrate have to be estimated in soils containing much organic matter, the strong sulphuric acid in the reagent chars the organic matter and makes it exceedingly difficult to match exactly the tints from the soil extracts with those given by the standard nitrate solutions.