The Florida agriculturist. [volume] (DeLand, Fla.) 1878-1911, 1884-12-10
Gypsum-what is it9r

WHAT III DOES NOT Do-wIEAT IT DOES.
j. A. r., wishes to know what plaster
(gypsum) is good for. There are always
many farmers desiring to know the
same thing, which is perhaps of more
than usual interest because of some erro-
neous belief in regard to its use and eff
fects. Gypsum is a rock, salt OF lime,
commonly called sulphate of lime, and
consists naturally OF 1916 per cent OF sui
phuric acid, and 500 per cent OF water.
The water is chemically combined and
connot be separated except by heat
which changes it to steam, when the
rock is broken up and falls to powder ;
or, if it is ground into powder and heat
ed in iron kettle, the steam escapes just
as it does from boiling water, in bubbles
and putfs until the water is all evap-
grated.
1t is important that this fact should
be noted, because it disposes of a COM
mon error, viz. That one use OF plaster
is to absorb water from the air and so
keep the soil moist in a dry season.
When the plaster has been calcined or
boiled, it has parted with its water OF
combination or crystallization depends,
and becomes y per cent lighter. In this
state gypsum is plaster and is used by
masons for making the hard finish on
plastered walls. 1t makes this hard fin
ish by combining again with the q per
cent of water which it has a natural af-
finity for, and which enables it to cohere
in hard, solid mass again. But in its
natural state it will not take any more
water, no more in fact, and not as much
as sand or soil would do, and therefore,
in the condition in which it is used as IL
fertilizer, it can have no beneficial effect
i'll gathering moisture for crops. When
however, it goes in the soil and decom
poses, it will, of course, part with its
combined water, it is true, and the far
mer who puts 100 pounds of plaster per
acre on his clover, may contribute Just
p pounds, or less than ten quarts of
water, to that acre of surface-an en-
tirely insignificant quantity for any prac-
teal use.-Plaster, then, for the farmers
use consists OF 32l:, per cent OF lime and
49,. per cent OF sulphuric acid, when it
is pure. Usually it contains some car
Donate of lime, silica, and sometimes
sulphate OF iron. When quite pure it
forms the beautiful semi-transparent al
abaster, and in one form in which it is
free from water, it forms the handsome
Sparkle stone called selentine or ''moon-
stone" from its full moon-like lustre.
OF itself, then, plaster can only con-
tribute to the food of plants. |. Its
own substance, viz. The sulphate of
lime; ,. Sulphuric acid 3. Lime That
is the extent of its direct usefulness.
But this is by no means inconsiderable,
for the mineral portion OF many plants,
form the most valuable nutrftive ele-
ments OF plants and animals. On this
accout, the 49, pounds OF sulphuric
acid contained in an average dressing of
100 pounds per acre of plaster will be of
great value. The 52ta per cent of dress
ing is also useful as far as it goes, and is
by no means unworthy of considerations
From these facts it is seen that while
plaster is always one of the useful fer
tilizers, at the same time it is one of
those that are at times indispensable. it
may be also seen that the common but
erroneous opinion that it is exhaustive
to the soil, only applies to its applica-
ton to very poor soils for the purpose of
extracting the last drop Of available fer
tility in them.-H. Stc,Cart, al Country
GPHtlPUl0n