Variation in Quality. Limestones vary widely in purity. They were formed under water, and clay and sand were laid down with the lime in such quantity in some cases that the resulting stone is not worth handling for soil improvement. A stone that is practically all carbonate of calcium, or a combination of calcium and magnesium, is wanted because it is these two elements that give value to the material. If a poor stone is used, too much waste matter must be handled. Twenty-five per cent more ground limestone of 80% purity must be applied than would be required in the case of an absolutely pure limestone. Any stone above 90% pure in carbonate of lime and magnesia is rated as good, but the best stone runs from 96% to 99%.

Limestones vary greatly in ability to resist disintegration, and this variation is a big factor in determining the agricultural value of ground limestone that has not been reduced to a fine powder. Particles of a hard limestone may lie inert in the soil for many years. Hardness also affects the cost of grinding.

A Matter of Distribution. Nature has used various agencies in reducing limestone for the making of soils. The stone contained its lime in carbonate form, and when reduced to good physical condition for distribution it helped to make highly productive land. We know that lime carbonate does the needed work in the soil so far as correction of acidity is concerned, but in the form of blocks of limestone it has no particular value to the land. Burning and slaking afforded to man a natural means of putting it into form for distribution, and it is only within recent years that the pulverization of limestone for land has become a business of considerable magnitude. The ground limestone used on land continues to be in part a by-product of the preparation of limestone for the manufacture of steel, glass, etc., and the making of roads, the fine dust being screened out for agricultural purposes. These sources of supply are very inadequate, and too remote from much land that requires treatment. Large plants have been established in various parts of the country for the purpose of crushing limestone for use on land, and quite recently low-priced pulverizers for farm use have come upon the market and are meeting a wide need.

Low-Priced Pulverizers. A serious drawback to the liming of land is the transportation charge that must be paid where no available stone can be found in the region. Great areas do have some beds that should be used, and a low-priced machine for pulverizing it is the solution of the problem. Such a machine must be durable, have ability to crush the stone to the desired fineness and be offered at a price that does not seem prohibitive to a farmer who would meet the demands of a small farming community. In this way freight charges are escaped, and a long and costly haul from a railway point is made unnecessary. The limestone of the locality will be made available more and more by means of this type of machine, and the inducement to correct the acidity of soils will be given to tens of thousands of land-owners who would not find it feasible to pay freight and cartage on supplies coming a long distance. There should be a market many times greater than now exists for the product of all large plants, while the number of small pulverizers multiplies rapidly. The very large areas that have no limestone at hand must continue to buy from manufacturers equipped to supply them, and farmers within a zone of small freight charges should be able to buy from such manufacturers more cheaply than they could pulverize stone on their own farms.

An individual, or a group of farmers, will buy a machine for pulverizing limestone at a cost of a few hundred dollars when costly equipment would be out of the question. If he has a bed of limestone of fair quality, and the soil of the region is lacking in lime, an efficient grinder or pulverizer solves the problem and makes prosperity possible to the region. Within the last few years much headway has been made in perfecting such machines, and their manufacturers have them on the market. Any type should be bought only after a test that shows capacity per hour and degree of fineness of the product. As a high degree of fineness is at the expense of power or time, and as the transportation charge on the product to the farm is small, there is no requirement for the fineness wanted in a high-priced article that must be used sparingly.

The aim should be to store in the soil for a term of years, and the coarse portion is preferable to the fine for this purpose because it will not leach out. The heavy application will furnish enough fine stuff to take care of present acidity. If nearly all the product of such a pulverizer will pass through a 10-mesh screen, and the amount applied is double that of very fine limestone, it should give immediate results and continue effective nearly twice as long as the half amount of finer material. There could hardly be a practical solution of the liming problem for many regions without the development of such devices for preparing limestone for distribution, and it is a matter of congratulation that some manufacturers have awakened to the market possibilities our country affords.