The use of the various forms of lime will become general,
and the terms employed to designate them should be understood. They
vary in their content of acid-correcting material, and their correct
names should be used with accuracy.
Stone-lime, often called lump-lime or unslaked lime, or calcium oxide
or CaO, is a form widely known, and may be taken as a standard. It is
the ordinary lime of commerce, and is obtained by the burning of
limestone. One hundred pounds of pure limestone will produce 56 pounds
of stone-lime (CaO).
Pulverized lime, often called ground lime, is stone-lime after being
pulverized to permit even distribution. When it is fully exposed to the
air or moisture, it slakes and doubles in volume.
Hydrated lime, often called slaked lime, is a combination of
stone-lime and water. The water causes an increase in weight of 32 per
cent, 56 pounds of stone-lime becoming 74 pounds of the hydrate.
Pulverized limestone, often called carbonate of lime, is the unburned
limestone made fine so that good distribution may be possible.
Air-slaked lime, often called carbonate of lime, is stone-lime or
hydrated lime combined with carbonic acid from the air, and thereby
increased in weight. Fifty-six pounds of stone-lime, or 74 pounds of
hydrated lime, become 100 pounds of air-slaked lime.
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
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.
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