42 
BULLETIN 1147, IT. S. DEPARTMENT OE AGRICULTURE. 
RELATION OF WATER-SOLUBLE ARSENIC TO TOXICITY OF ARSENICALS. 
No perceptible differences in mortality which could be attributed 
to the usually small differences in water-soluble arsenic oxid were 
observed in the 11 commercial acid lead arsenates used in the pre- 
liminary tests. Three of these arsenates which have high percent- 
ages of water-soluble arsenic oxid, however, killed no more insects 
than the others. 
Table 20. — Relation of water-soluble arsenic to toxicity of arsenicals, 1919. 
Insects tested. 
Water- 
Food 
eaten 
per 
soluble 
Toxicity 
insect 
arsenic, 
after de- 
(esti- 
Sample 
No. 
Arsenicals and control. 
based 
on total 
ducting 
mor- 
mated), 
based 
Number. 
Species. 1 
arsenic 
in 
sample. 
tality of 
control. 
on web- 
worms 
and tent 
cater- 
pillars. 
Per cent. 
Per cent. 
Units. 
18 
1,184 
1,939 
1,361 
1,529 
1,516 
1,441 
sftl 
1 15 
21 5 
68 6 
28 
do . 
1.73 
60 9 
10 9 
68 
do.... 
.57 
59.6 
17 6 
9 
do 
17 77 
46 1 
9 6 
10 
Pure arsenic oxid 
...do 
...do 
100.00 
1.25 
76.5 
66.9 
3 5 
23 
CnmmerHal zinc arsenite 
22.0 
70 
Commercial acid lead arsenate (new 
process) 
422 
sfl 
.69 
66.9 
2.8 
39 
Commercial acid lead arsenate 
2,263 
2,645 
2,492 
sftlg 
...do 
...do 
.61 
.41 
.88 
68.9 
70.0 
39.9 
2.9 
9 1 
7 
do 
66.0 
56 
do 
2,373 
2,393 
...do 
...do 
1.31 
.20 
59.2 
60.1 
30.8 
57 
do 
29.9 
58 
do 
2,114 
2,657 
...do 
...do 
.52 
5.20 
43.1 
65.9 
68.1 
59 
do 
18.5 
69 
Laboratory calcium arsenate 
2,298 
...do 
.88 
52.5 
55.0 
45 
1,232 
1,758 
ft 
...do 
.04 
89.26 
3.6 
81.2 
99 9 
46 
Laboratory monocalcium arsenate 
2.0 
55 
Laboratory sodium arsenate plus Bor- 
deaux mixture 
2,674 
sflgy 
61.7 
5.0 
64 
2,059 
1,651 
...do 
flgy 
3.52 
4.64 
65.5 
50.2 
3.2 
62 
Cfrmmprn'al magnesium arsenatp, , . 
18.3 
71 
Laboratory barium arsenate 
1,706 
...do 
.68 
43.6 
22.2 
74 
Laboratory copper barium arsenate 
1,814 
...do 
6.27 
4S.9 
15.6 
73 
1,482 
fly 
1.91 
39.3 
16.1 
Control with food 
100.0 
is, silkworms; f, webworms (E. cunea); t, tent caterpillars; 1, potato-beetle larvae; g, grasshoppers; and 
y, webworms {H. tertor). 
Table 20 shows that those arsenicals which are readily water 
soluble (samples 10 and 46) have extremely high percentages of 
toxicity, but that some of those which are almost insoluble in water 
(samples 5, 23, and 39) have percentages of toxicity nearly as high. 
The toxicity of the insoluble arsenicals does not appear to be based 
upon the water-soluble arsenic present, but upon the stability of 
the compound and how readily it can be broken down in the bodies 
of insects. 
During all of these experiments no special stud} 7 of the burning 
effects of the many arsenicals sprayed on foliage was made. The 
percentage of water-soluble arsenic is generally taken as a criterion 
for judging the burning effect on foliage. The following spray 
mixtures badly burned wild-cherry foliage: Sodium and potassium 
arsenates, sodium arsenate plus Bordeaux mixture, all the samples 
of arsenious and arsenic oxids used, calcium arsenates (samples 5, 
