correct all acidity, and
the use of such material to free plant food in humus sufficiently to
produce heavy sods, are just as good farm practices as drainage and the
application of manure.

[Illustration: Laying Foundation for a Lime Stack at the Pennsylvania
Experiment Station]

[Illustration: A Stack Nearly Completed at the Pennsylvania Experiment
Station]

CHAPTER XI

BURNING LIME

_Methods of Burning._ Limestone contains the calcium and magnesium that
must be the chief source of supply of American soils, though marls,
ashes, etc., have their place. The burning of the stone has been the
leading means of bringing it to a condition of availability to the soil,
excepting, of course, the vast work of disintegration carried on through
all the ages by nature. Pulverization of the rock by machinery for use
on land is recent.

The devices for burning are various, a modern lime plant containing
immense kilns, cylindrical in form, the stone being fed into them at the
top continuously, and the lime removed at the bottom. A large part of
the lime that is sold for use on land is made in plants of this kind.
Some is burned in kilns of cheap construction, but a traveler through a
limestone country finds few such kilns now in use.

_The Farm Lime Heap._ A common method of producing lime for farm use
has been, and continues to be, a simple and inexpensive one, involving
the use only of wood, coal and limestone, with earth as a covering. Dr.
Wm. Frear, chemist of the Pennsylvania station, in Bulletin 261 of the
Pennsylvania department of agriculture, describes a method of burning
lime on the farm as follows: "A convenient oblong piece of ground is
cleared, and leveled if need be, to secure a fit platform. Upon this
level is placed a layer or two of good cord wood, better well seasoned,
arranged in such manner as to afford horizontal draught passages into
the interior of the heap. Between the chinks in the cord wood, shavings,
straw or other light kindling is placed. The stone having been reduced
to the size of a double fist, sometimes not so small, is laid upon the
cord wood, care being taken to leave chinks between the stones just as
between the bricks in a brick kiln. It is preferred that this layer of
stone should not exceed six to ten inches in thickness.

"In some cases, temporary wooden flues, filled with straw, are erected,
either one at the center or, if the heap is elliptical, one near each
end, and the st