During this season the rivers, which are roaring torrents throughout the monsoon, are almost all lost in the dry, absorbent plains.
The subsoil too is differently formed: the surface consists of very absorbent materials, then comes a stratum of less permeable tufa or peperino (sometimes clay is present), and below that again more permeable materials.
In one the absorbent is placed at the bottom, and the substance to be dried above.
In special cases, such as the preparation of edible oils and fats, a further improvement in colour and greater purity is obtained by filtering the oils over charcoal, or over natural absorbent earths, such as fuller's earth.
The early segmentation of the embryo differs in the several groups, but usually the first leaf or leaves, the apex of the stem and the first root are differentiated early, while a special absorbent organ (the foot) maintains for some time the physiological connexion between the sporophyte and the prothallus.
In both Psilotum and Tmesipteris the functions of the root-system, which is completely absent, are performed by leafless rhizomes bearing absorbent hairs and inhabited by an endophytic fungus.
They may be separated in a similar way by concentrated sulphuric acid, which has the same absorbent effect on the one class, and not on the other.
On the other hand, water should be given generously in hot weather, also when absorbent stone is used or when the concrete is not rammed.
Kieselguhr, for it is too valuable as an absorbent of nitroglycerine, for the manufacture of dynamite, to be available for making pozzuolanic cement.
The soil of yards and the floors and walls of houses rapidly become contaminated, and the ideal condition would be to have an impermeable flooring covering the whole area, and supplied with suitable layers of sand, sawdust, peat-moss or other absorbent substances which can be changed at frequent intervals.