"No, this test does not prove that," said Percy. "It only proves that they are not present as limestone. Calcium may be present in other compounds, especially in silicates, which are the most abundant compounds in the soil and in the earth's crust; and, as indicated by the ending _-ate, _oxygen is contained in calcium silicate as well as in calcium carbonate." "I see; the subject is much more complicated than I thought." "Somewhat, perhaps," Percy replied; "but yet it is quite simple and very easily understood, if we only keep in mind a few well established facts. Certainly the essential science of soil fertility is much less complicated than many of the political questions of the day, such as the gold standard or free-silver basis, the tariff issues, and reciprocity advantages, regarding which most farmers are fairly well informed,--at least to such an extent that they can argue these questions for hours." "I think you are quite right in that," said Mr. West. "Of course, it is important that every citizen entitled to the privilege of voting in a democracy like ours should be able to exercise his franchise intelligently; but the citizen who is responsible for the management of farm lands ought surely to be at least as well informed concerning the principles which underlie the maintenance of soil fertility; provided, of course, that such knowledge is within his reach; and from what you say I am beginning to believe that such is the case. At any rate this simple test seems to show conclusively that this soil contains no limestone, and it is common knowledge that limestone soils are good soils." Percy took up the ball of soil containing the slip of blue paper, broke it in two again, and it was seen that the paper had changed in color from blue to red "There's a change, for certain," said Mr. West, "that has some meaning to you I suppose." "This is litmus paper," said Percy. "It is prepared by moistening specially prepared paper with a solution of a coloring matter called litmus, and the paper is then dried. This coloring matter has the property of turning blue in the presence of alkali and red in the presence of acid. The blue paper is prepared with a trace of alkali, and the red paper with a trace of acid. If more than a trace were present the litmus paper would not be sufficiently sensitive for the test. "This little bottle containing two dozen slips of paper cost me five cents, and it can be obtained at most drug stores.