Arsenic Toxicity Studies —Clements and Munson 
155 
on a black alluvial soil treated with 
various increments of arsenic. 
MATERIALS AND METHODS 
Culture solutions .—For Part I and Part II 
mentioned above, water cultures were used. 
A total of 30 crocks was used for each of the 
three species—10 crocks at each of three 
phosphorus levels—with each crock having 
a known concentration of arsenic in the form 
of sodium arsenite in the study of the triva- 
lent form and sodium arsenate in the study 
of the pentavalent form. 
The experiments were conducted in a 
greenhouse of the University of Hawaii 
Agricultural Experiment Station. Four- 
gallon size glazed crocks were used for the 
Sudan grass and tomato samples, and 2-gal¬ 
lon size for the bean. Distilled water was 
used throughout and continuous aeration 
maintained. The plants were held in corks 
set into lids which fitted over the crocks. 
The tomato and Sudan grass seeds were 
germinated on cheesecloth and transferred 
when large enough to facilitate handling 
without injury. The bean seeds were germi¬ 
nated in black sand and transplanted as soon 
as was practicable. 
All the plants were given complete nutri¬ 
ents for 2 weeks. The following solutions 
were used: 
0 SUDAN 
TOMATO GRASS BEAN 
Ca(N0 3 ) 2 .005M .005M .005M 
KNOs .005M .005M .005M 
MgSOi.002M .002M .002M 
CaCl 2 . .003M .003M - 
KHsPCL ..001M .001M .002M 
Iron (as FeS0 4 ) and standard amounts of 
copper, manganese, zinc, and boron were 
added. 
After 2 weeks passed the solutions were 
changed, but the nutrients as listed above 
were maintained with the exception of 
the phosphate, which was added in the 
amount required in the experiment. The 
arsenic increments were added as planned, 
and the plants were selected for uniformity 
and thinned to three plants per crock for 
the bean and Sudan grass and two plants for 
the tomato. All solutions were changed 
weekly, and the levels of all salts were 
maintained as required in the experiment. 
Plants which did not live until the end 
of the experiment were removed when they 
died. All others were allowed to grow for 
3 to 4 weeks after the original treatment; 
then they were harvested. Green weights of 
the plant tops were taken, after which the 
plants were dried and dry weights taken. 
The material was ground in a Wiley mill 
and stored for subsequent arsenic and phos¬ 
phate analyses. 
Methods of analysis .—The method of Cas- 
sil and Wichmann (1939) was used in 
making the arsenic determinations reported 
in this paper. For the phosphate determina¬ 
tions, the Truog and Meyer (1929) modi¬ 
fication of the Deniges method was used. 
The dry plant material was digested as 
follows: Two grams or less of the sample 
were added to 125 cc. Erlenmeyer flasks, fol¬ 
lowed by 10 cc. of H 2 S0 4 and 20 cc. of 
HN0 3 . The flasks were allowed to stand for 
several hours, then heated slowly. Five-cc. 
increments of HNO s were added, and the 
digestion continued until the solution was 
clear and yellow. A final 5 cc. of HNO s was 
added with 5 drops of perchloric acid and 
heat was applied until dense white SO s 
fumes were evolved. The flask was removed 
and cooled, and the solution made up to 
125 cc. From this, suitable aliquots were 
taken for the arsenic and phosphate deter¬ 
minations. 
DATA AND DISCUSSION 
Part I. Comparative Toxicity of Trivalent 
and Pentavalent Arsenic 
In Tables 1, 2, and 3 are presented data 
for experiments using the three species 
treated with sodium arsenate (Na 2 HAs0 4 . 
