As Way had succeeded in producing an artificial hydrated silicate possessing absorptive properties, Eichorn[88] thought of trying natural hydrated silicates or zeolites and found that they exhibited the same power as Way’s artificial preparation. It has also been shown by Biedermann,[89] Rautlenberg,[90] and Heiden[91] that the absorptive power bears a close relation to the amount of soluble silicates present. In view of these facts it is now generally accepted that the absorption of salts of the alkalies, accompanied by the change of base, is due chiefly to the presence of decomposed zeolite minerals in the soil. Besides the purely chemical absorption of salts by the soil, we have a physical absorption of various substances similar to the action of charcoal when used as a filter. =127. Conclusions of Armsby.=—The data connected with the absorption of bases by a soil have also been reviewed by Armsby.[92] He shows that the absorption is accompanied by a chemical reaction between the salt whose base is absorbed and some constituent of the soil, and this change seems to be due particularly to certain zeolitic silicates, although Liebig and others were disposed to credit this absorption largely to physical causes. Knop advances the idea that the soil has the power of disintegrating salts in the presence of some substances like calcium carbonate which can unite with the acid. In experiments made with hydrous silicates it was shown that the absorption resembled in all cases like phenomena in the soil; hence the supposition already advanced in regard to the influence of such silicates is doubtless true. In respect of absorption in general, the following conclusions were reached: 1. The absorption of combined bases by the soil consists in an exchange of bases between the salt and the hydrous silicates of the soil. 2. This exchange, which is primarily chemical, is only partial, its extent varying (a) with the concentration of the solution, and (b) with the ratio between the volume of the solution and the quality of soil used. 3. The cause of these variations is probably the action of mass or the tendency of resulting compounds to re-form the original bodies, the absorption actually found in any case marking the point where the two forces are in equilibrium.