_Agricultural lime_, or land-lime, may embrace anything that the manufacturer of lime chooses to market. It may be reasonably pure unslaked lime, or it may have less value than a finely pulverized pure limestone. There is a custom of grinding the core, or partially burned limestone of the kiln, together with impurities removed from builders' lime, and with this may be put some air-slaked lime. Some manufacturers market under this name a lime of excellent value. There is no standard, and one should not pay more than a finely pulverized pure limestone would cost unless he knows that the content of fresh burned lime is high. The element with which we are concerned in any of these forms of lime is calcium. It is the base whose union with the acids destroys the latter. It should be obvious that the addition of water to stone-lime, which adds weight and causes 56 pounds of the stone-lime to become 74 pounds of hydrated lime, adds no calcium. Likewise the change to the air-slaked condition adds no calcium, but again adds weight. The Kind to Apply.--If a soil contains free acid, the amount of calcium needed is definite. The form of lime that can supply the need in that particular field at least expenditure of money and trouble is the one to be selected. A ton of stone-lime, or pulverized lime, can correct as much acid as 2640 pounds of hydrated lime or 3570 pounds of pulverized limestone, if all the original material was pure. In other words, if the value of a given weight of pulverized limestone is placed at 100, the value of the same weight of hydrated lime would be 132 and the value of stone-lime would be 180, when each was finely divided and distributed throughout the surface soil. The Fineness of Limestone.--Experiments at the Pennsylvania experiment station have shown that limestone has practically immediate availability in an acid soil if all of it has ability to pass through a screen having 60 meshes to the linear inch. Much of the limestone meeting this test doubtless is fine enough to pass through an 100-mesh screen. The requirement that a 60-mesh screen be used in testing is a satisfactory one to the buyer that wants immediate results in the field. A coarser product must be used in larger amount per acre, as only the fine particles are available at once, and the object of the application is to correct all the acidity. Where a coarse product, containing some fine particles, can be used at such a low price per ton that the application may consist of a large number of tons per acre, the practice may be commended, but the essential thing is immediate results, and only finely divided limestone can give them. Any long railway or wagon haul makes a heavy application of coarsely pulverized limestone inexpedient.