In the course of these experiments, several different soils were operated upon, and it was found that all soils capable of profitable cultivation possessed this property in a greater or less degree. Pure sand, it was found, did not possess this property. The organic matter of the soil, it was proved, had nothing to do with it. The addition of carbonate of lime to a soil did not increase its absorptive power, and indeed it was found that a soil in which carbonate of lime did not exist, possessed in a high degree the power of removing ammonia or potash from solution. To what, then, is the power of soils to arrest ammonia, potash, magnesia, phosphoric acid, etc., owing? The above experiments lead to the conclusion that it is due to the _clay_ which they contain. In the language of Prof. Way, however, “It still remained to be considered, whether the whole clay took any active part in these changes, or whether there existed in clay some chemical compound in small quantity to which the action was due. This question was to be decided by the extent to which clay was able to unite with ammonia, or other alkaline bases; and it soon became evident that the idea of the clay as a whole, being the cause of the absorptive property, was inconsistent with all the ascertained laws of chemical combination.” After a series of experiments, Prof. Way came to the conclusion that there is in clays a peculiar class of double silicates to which the absorptive properties of soil are due. He found that the double silicate of alumina and lime, or soda, whether found naturally in soils or produced artificially, would be decomposed when a salt of ammonia, or potash, etc., was mixed with it, the ammonia, or potash, taking the place of the lime or soda. Prof. Way’s discovery, then, is not that soils have “absorptive properties”--that has been long known--but that they absorb ammonia, potash, phosphoric acid, etc., by virtue of the double silicate of alumina and soda, or lime, etc., which they contain. Soils are also found to have the power of absorbing ammonia, or rather _carbonate_ of ammonia, from the air. “It has long been known,” says Prof. Way, “that soils acquire fertility by exposure to the influence of the atmosphere--hence one of the uses of fallows. * * I find that clay is so greedy of ammonia, that if air, charged with carbonate of ammonia, so as to be highly pungent, is passed through a tube filled with small fragments of dry clay, _every particle of the gas is arrested_.” This power of the soil to absorb ammonia, is also due to the double silicates. But there is this remarkable difference, that while either the lime, soda, or potash silicate is capable of removing the ammonia from _solution_, the _lime_ silicate alone _has the power of absorbing it from the air_.