"Alkali and acid are exactly opposite terms, like hot and cold. The one neutralizes the other. This test with litmus paper is a test for soil acidity, and the fact that the moisture of the soil has turned the litmus from blue to red shows that this soil is acid, or sour. The soil moisture contained enough acid to neutralize the trace of alkali contained in the blue paper and to change the paper to a distinctly light red color; and the fact that the paper remains red even after drying, shows that the soil contains fixed acids or acid salts, and not merely carbonic acid, which if present would completely volatilize as the paper dries. "Now, these two tests are in harmony. The one shows the absence of limestone, and the other shows the presence of acidity, and consequently the need of limestone to correct or neutralize the acidity, for limestone itself is an alkali." "But limestone soils are not alkali soils, are they?" asked Mr. West. "Not in the sense of containing injurious alkali, like sodium carbonate, the compound which is found in the 'black alkali' lands of the arid regions of the far West; but chemically considered limestone is truly an alkali; and, as such, it has power to neutralze this soil acidity." "Is the acidity harmful to the crops?" "It is not particularly harmful to the common crops of the grass family, such as wheat, corn, oats, and timothy; but some of the most valuable crops for soil improvement will not thrive on acid soils. This is especially true of clover and alfalfa." "That is certainly correct for clover so far as this kind of soil is concerned," said Mr. West. "Clover never amounts to much on this kind of land, except where heavily fertilized. When fertilized it usually grows well. Does the farm fertilizer neutralize the acid?" "Only to a small extent. It is true that farm manures contain very appreciable amounts of lime and some other alkaline, or basic, substances, but in addition to this, and perhaps of greater importance, is the fact that such fertilizer has power to feed the clover crop as well as other crops. In other words it furnishes the essential materials of which these crops are made. In addition to this the decaying organic matter has power to liberate some plant food from the soil which would not otherwise be made available although to that extent the farm manure serves as a soil stimulant, this action tending not toward soil enrichment but toward the further depletion of the store of fertility still remaining in the soil." "This seems a complicated problem," said Mr. West, "but may I now show you some of our more productive land?"