A Simple Method of Demonstrating the Action of Lime in Soils 1

Every demonstrator or lecturer realizes the fact that the more vividly he paints his word pictures the more lasting is the impression made on his audience. If the lecture is illustrated it is better understood, even with a poor lecturer, than if not, and the closer the illustrations are to the point the better. While demonstrating methods for testing soils and determining their lime requirements at a large State fair recently, the writer was asked this very pointed question: " How can you prove to me that limestone has a beneficial action in the soil by neutralizing the acidity ?" The questioner was of the type that demands to be shown rather than told, and his question was answered in the following manner. A few drops of sodium Mazarin sulfonate (alazarin red) indicator was put into about IOO c.c. neutral water in a flask. The farmer was asked to note the resulting bro~vn color and also any other change of color that might subsequently appear. Approximately 2 grams of ground limestone were then dropped into the water and the flask thoroughly shaken. Naturally the characteristic alkali color appeared. This state was assumed to be that of a soil in good tilth. But practically all farming operations tend toward an acid reaction, so a few drops of dilute hydrochloric was added. The farmer was quick to note the solution’s change from red to yellow, but when the flask was agitated a few times and the alkali color returned, he was amazed. When the phenomenon was explained to him in a manner that applied to the soil, he was apparently convinced that the beneficial action of limestone in the soil continued as long as there was any present. This demonstration proved to be very popular and absolutely settled a number of arguments. It is hoped that lecturers on limes and lim̄ ing will be able to make use of the method, as the materials required take up little room and are found in practically all laboratories.