rial that would not pass through a 60-, or 40-, or 10-mesh
screen, but it does contain a big percentage of immediately available
lime, and a more complete pulverization of this by-product would add
greatly to its cost.

It is quite possible that a ton of such stone may be bought at a price
that would cover the value only of the fine portion, estimated on the
basis of the prevailing price of finely ground material, the coarse
material being obtained without any cost at all. It is this situation,
or an approach to it, that leads some authorities to become strenuous
advocates of the use of coarsely pulverized stone. The advice is right
for those who are in a position to accept it. If the money available for
liming an acre of land can buy all the fine stone needed for the present
and some coarser stone mixed with it for later use by the soil, the
purchase is much more rational than the investment of the same amount of
money in very fine stone that has no admixture of coarser material. If
the investment in the former case is larger than in the latter, it
continues to be good business up to a certain point, and the room for
some uncertainty is wide enough to provide for much difference in
judgment.

_Quality of the Stone._ Another factor of uncertainty is the hardness of
the stone. A limestone may have such flinty characteristics that a piece
barely able to pass through a 10-mesh screen will not disintegrate in
the soil for years, and there are other types of limestone that go into
pieces rapidly. The variation in quality of stone accounts for no little
difference in opinion that is based upon limited observation.

_Using One's Judgment._ It is evident that no hard and fast rule
respecting fineness may be laid down, and yet a rather definite basis
for judgment is needed. There is much good experience to justify the
requirement that when all ground lime is high-priced in any section for
any reason, and the amount applied per acre is thereby restricted, the
material should be able to pass through a screen having 60 wires to the
linear inch, and that the greater part should be much finer. Usually
some part of such stone will pass through a 200-mesh screen. When a
limestone on the market will not meet this test, some concession in
price should be expected. If the stone is not very flinty, a 40-mesh
screen may be regarded as affording a reasonably satisfactory test.

An increasing percentage of coarser material makes necessary