Slaking Lime. The usual means of reducing fresh burned stone lime to a
condition that makes even distribution upon land possible is by slaking.
A few years ago considerable effort was made to create a market for lime
pulverized by machinery, but the
difficulty in excluding the moisture of
the air so that packages would not burst has been in the way of
developing a market. Slaking, by the addition of water to the fresh
burned lime, is the common method of getting the required physical
condition. When the slaking is done on the farm, the custom has been to
distribute the lime in small piles in the field, placing the piles at
such convenient distance apart that the lime, after slaking, could be
spread easily with a shovel.
The water for slaking comes from rains, or from moisture in the air and
earth. The method is wasteful and can be justified, if ever, only where
farm-burned lime costs little per ton, and the nature of the soil is
such that a relatively heavy application can be safely made. The
distribution is necessarily uneven, and if the required amount goes upon
all the surface, a great excess is sure to go upon a portion of it. Very
often an excess of water puddles much of the lime in the pile, and lumps
may be seen lying in ineffective form in the soil for years. The
practice is responsible for much of the excessive application that
brought the use of caustic lime into disrepute.
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.
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