It is generally recognised that the mechanical analysis of soils containing large quantities of organic matter presents considerable difficulties and that in the case of peaty soils mechanical analysis can have little significance. Apart from the masking effect of organic matter on soil properties which will naturally vitiate any correlations with mechanical composition, the actual dispersion of humus soils is difficult owing to the cementing action of humified organic matter, whereby soil particles are aggregated together into compound structures which resist ordinary methods of dispersion. Various methods have been suggested for the destruction of organic matter as a preliminary to mechanical analysis. Atterberg recommends the use of alkaline sodium hypobromite solution. In the case of diatomaceous soils, however, oxidation of the organic matter with hot nitric acid (d. 1·14) is recommended. For soils free from calcium carbonate the use of hydrochloric acid (d. 1·12) is suggested.