_Slaking in Large Heaps._ A preferable method is to put the lime in flat heaps of large size and about four feet deep, so that water may be applied or advantage be taken of rainfall. The value of the lime is so great that one can well afford to draw water and apply with a hose so that the quantity can be controlled with exactness. When fresh burned lime is perfectly slaked, each 56 pounds of pure lime becomes 74 pounds of hydrated lime, water furnishing the added weight. _Hydrated Lime on the Market._ A popular form of lime on the market is the hydrate. Manufacturers first burn the stone, and in the case of a pure limestone they drive off 44 pounds of each 100 pounds of the weight in burning. Then, they combine enough water with the lime to change it to hydrate form, and that adds 18 pounds weight. It is run through a sieve to remove any coarse material, and then packed in bags which help to exclude the air. The small packages in which it comes upon the market make handling easy, and this helps to bring it into demand. Its good physical condition makes even distribution possible, and thus permits maximum effectiveness to be obtained. It is only slaked lime, identical in composition and value with lime of the same purity slaked on the farm, but some dealers have been able to create the impression that it has some added quality and peculiar power. This does no credit to the public intelligence, but the hunger of soils for lime is so great that investment at a price wholly out of proportion to the price of farm-slaked lime has rarely failed to yield some profit. _Degree of Purity._ It is always a reasonable assumption that hydrated lime has been made from stone of a good degree of purity. A local stone, burned on the farm, may be of low grade, but no man of business judgment would erect a costly plant for burning and hydrating lime where the purity of the stone would not afford a good advertisement in itself. On the other hand, we find very little hydrated lime on the market that has not had sufficient exposure to the air to become changed in some part to an air-slaked condition, or has had refuse mixed with it. Air-slaked lime is not worth as much per ton as the hydrate because it cannot correct as much soil acidity, and the percentage of the former cannot be determined by the buyer. Its presence may not be due to any wrong-doing of the manufacturer, and, on the other hand, the increase in weight that attends air-slaking may be welcomed in some degree by a dishonest manufacturer before the goods are shipped. The difficulty in preventing hydrated lime from adding to its weight by becoming air-slaked is a point to be taken into consideration. The percentages of air-slaked material in hydrated limes are widely variable, and no manufacturer can standardize his product on the market surely for the benefit of the farmer. In some instances the product is adulterated with refuse material in finely pulverized condition. CHAPTER XIII