The functions and importance of calcium and magnesium supplied to the soil by liming have been discussed in detail by Fippin (10). We shall merely summarize this phase of the subject by saying that liming increases the efficiency of utilization of the available water and fertility of the soil by correcting some factors unfavorable to plant growth, making possible more economical crop production and tending to conserve the soil. Only the basic calcium and magnesium compounds—the oxides, hydroxides, and carbonates (and possibly certain silicates, such as blast furnace slag)—are to be included under the term “liming materials.” Ground burned lime was formerly in favor, but is no longer of much importance in agriculture. Hydrated lime is still used to a considerable extent where a concentrated and very quickly active lime is desired. Its extreme fineness and bulk make it easy to spread at light rates, and the temporarily very high pH value resulting from heavy applications may have a sterilizing effect, not shown by ground limestone, against certain plant diseases. The total neutralizing power (T.N.P.) of hydrate and other liming materials, expressed as the equivalent percentage of calcium carbonate (C.C.E.), should always be specified rather than the contents of total oxides only, as is sometimes done, as the latter permits no comparison of value without calculation. Ground limestone, the cheapest and usually the most economical agricultural lime, is offered in several grades, both dolomitic and high-calcium, at prices naturally increasing with the expense of finer grinding and of drying necessary for this operation, and of marketing in bags. Meal and agricultural ground limestone can be produced from undried rock, shipped in open cars, and piled in the field—factors conducive to low cost per ton spread. But for quick effects, these grades must be applied at a heavier rate which may be less profitable than a lighter application of a higher grade liming material. High-magnesium limestone is known to be less rapidly active in the soil, but is usually of higher potential activity as indicated by the total neutralizing power, and some soils, chiefly in the eastern seaboard states, are in great need of the element, magnesium. It is generally accepted that for equal effects a dolomite should be more finely ground than a high-calcium limestone, but little has been published on which to base an opinion as to the optimum fineness under a particular set of circumstances.