Feb. 7,1916 
Boron 
879 
Tests with tomato (Lycopdrsicon esculentum) and lettuce (.Lactuca 
sativa) were made on plants which had been grown in boxes in green¬ 
houses until they were 2 to 3 inches high, when they were transplanted in 
their respective pots containing the mixtures of manure and soil. The 
potatoes (,Solanum tuberosum) tested were of the Green Mountain variety 
and the seeds used in growing the other plants were common varieties. 
The percentages of boric acid as recorded in the tables are calculated 
to a water- and ash-free basis. At least four pots for each treatment 
were employed in the pot tests. The plots at Arlington Farm were one- 
twentieth of an acre and those in the South about one-sixtieth of an acre 
in size. The tests with lettuce were carried out in benches, each 3 by 5 
feet. 
DESCRIPTION OF METHODS 
Many tests for determining boron in foods and other material have 
been devised. When small amounts are present, as was the case in the 
present experiments, it is determined colorimetrically, using curcumin, 
the active principle in turmeric {Curcuma longa L.), a characteristic red 
color being given when boron is present. 
In preparing the samples, the roots were separated from the plants. 
Both roots and plants were washed, dried, and cut into small pieces for 
analysis. In some cases the fruit also was tested. In such instances it 
was washed, dried, and ground for analysis. Boron was determined by 
the use of freshly prepared strips of curcumin paper, prepared by immersing 
large unfolded filter paper in a 0.2 per cent alcoholic solution of curcumin. 
The procedure was as follows: About 3 gm. of a dried sample were treated 
with sufficient saturated lime water to make the reaction alkaline. After 
a thorough mixing in platinum dishes, the samples were dried and heated 
in a muffle until all of the organic matter had burned off. Ten c. c. of 
water and a little hydrochloric acid were added and the solution was 
warmed, filtered, washed, and made to 100 c. c. volume. A 50 c. c. 
aliquot was usually taken for the determination of the boron, but this 
varied according to the amount present. To the 50 c. c. aliquot, or a 
smaller aliquot diluted to 50 c. c., placed in small porcelain evaporating 
dishes, 2 c. c. of hydrochloric acid were added, and strips of curcumin 
paper were suspended and allowed to dip into those solutions to the 
depth of one-fourth of an inch. In all cases standard boric-acid solu¬ 
tions, as well as blanks, were simultaneously employed. After four 
hours the colors on the strips of paper were compared and the percentage 
of boric acid determined. 
In the case of soils, the boron soluble in weak hydrochloric acid, not 
the total boron, was determined. Fifty gm. of soil were shaken with 
200 c. c. of a solution of hydrochloric acid (1120) for one hour. This was 
filtered and 100 c. c. of the filtrate made alkaline with lime water, evapor¬ 
ated to dryness, and ashed. The ash was acidified with hydrochloric 
