Composition of Florida-Grown Vegetables 9

 Tomatoes were prepared by removing the calyx and washing.
Each tomato was halved and placed cut side up on cloth trays
for drying. Drying was started at 300 C. in a forced draft oven.
The temperature was gradually increased to 70 C. over a period
of 48 hours, then held for 24 hours. This method of drying
prevented the loss of juice. All other vegetable samples were
dried for 24 to 36 hours at 700. The samples were broken up by
hand when dry and stored in glass jars.
 Each sample was divided for analyses. One portion was
ground with a Wiley mill and used for the determination of total
nitrogen, potassium, calcium, magnesium and phosphorus. The
other portion was ground by hand with a poreclain mortar and
pestle for the determination of iron.
 Hood, Parks and Hurwitz (12) made an extensive study of
all kinds of laboratory grinding methods. They found that all
of the mechanical grinding methods tested resulted in serious
contaminations with 1 or more elements. Iron and copper con-
tamination made it impractical to use iron mills in minor ele-
ment work. Grinding by porcelain mortar and pestle was the
only method tested by them which appeared to give no serious
contamination.
 Methods of Analysis
 Chemical analyses of plant materials were run in duplicate,
using wet combustion with perchloric acid (10). Calcium was
precipitated as the oxalate and titrated with standard potassium
permanganate. Magnesium was precipitated as magnesium am-
monium phosphate and titrated with standard acid. Phosphorus
was determined colorimetrically by a molybdate blue method
(19). Potassium was determined by precipitation with sodium
cobaltinitrate and titration with permanganate (22). Iron was
determined colorimetrically by the use of the ferrous-ortho-
phenanthroline complex (9).
 Soil samples were analyzed for base exchange capacity and
exchangeable bases by leaching with neutral normal ammonium
acetate, as recommended by Peech (15), with the exception that
precipitation of potassium was by the same method as used for
the plant analysis. Phosphorus was determined by the Truog
(19) method. Soil moisture equivalent was determined by the
centrifuge method of Briggs and McLane (3). Organic matter
was determined by the wet combustion method of Walkley (23),
except for peat soils, in which the organic matter was determined