Soil improvements by burning

1232. The soils improved by burning are all such as contain too much dead vegetable fibre, and which consequently lose from one third to one half their weight by incineration; and all such as contain their earthy constituents in an impalpable state of division, i.e. the stiff clays and marls, are improved by burning: but in coarse sands, or rich soils containing a just mixture of the earths, and in all cases in which the texture is sufficiently loose, or the organisable matter sufficiently soluble, the process of torrefaction cannot be useful.