with a fine stone.

_Air-Slaking a Slow Process._ Lime changes to an air-slaked condition
slowly unless it has full exposure. Old heaps will remain in hydrate
form for many years, excepting the outside coat, which excludes the air.
Complete air-slaking would not reduce ability to correct soil acidity,
the total amount of calcium and magnesium remaining constant, but weight
would be added in the slaking, and therefore the value per ton would be
reduced. The slowness with which air-slaking proceeds gives reason to
expect that any bulk of old lime may contain a considerable percentage
of the hydrate, and therefore have greater strength than a true
carbonate like limestone. This is a consideration of value to a buyer.

_Agricultural Lime._ Some manufacturers have found in the demand for
lime by farmers an opportunity of disposing of much material that would
not be satisfactory to manufacturers and builders. In some cases this
so-called agricultural lime is sold at a price that is not beyond value,
but it varies much in its content of pure lime. If the unburned cores
of kilns are ground up, the material simply retains the value of
unburned stone. Any air-slaked material put into it has like value.
Forkings, ground up, have less value, and sometimes no value at all.
Some better material may go into this mixture that is given the name
"agricultural lime," and the product cannot be standardized or have a
valuation given it that would be true for another lot.

Some manufacturers are marketing limes of fair values under this
designation, but the values change as the material changes. There are
other manufacturers who are putting poor stuff on the market. Unless one
knows the manufacturer and his processes, he should not pay a great deal
for "agricultural lime." It is much better to buy a high-grade lime or
limestone that is more nearly constant in composition. When the word
"agricultural" is part of the brand, there is assurance that the
percentage of waste stuff in it is relatively high. Unless one knows to
the contrary, he should assume that a ton of finely pulverized limestone
is worth more per ton than "agricultural lime."

_Marl._ Marls vary in composition, as limestones do, but there are beds
of chalky marl that contain very little clay and sand and are nearly a
pure carbonate. It is only marls of high degree of purity that can be
put on the market with profit, but beds of less pure marl furnish
dressings for farms of th