42 
BULLETIN 1H7, U. S. DEPARTMENT OF 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 14 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. 
Sample 
No. 
Arsenicals and control. 
Insects tested. 
Number. 
Species. 1 
Water- 
soluble 
Toxicity 
arsenic, 
after de- 
based 
ducting 
on total 
mor- 
arsenic 
tality of 
in 
control. 
sample. 
Food 
eaten 
per 
insect 
(esti- 
mated), 
based 
on web- 
worms 
and tent 
cater- 
pillars. 
Laboratory basic lead arsenate 
Commercial basic lead arsenate 
Laboratory acid lead arsenate 
Pure arsenious oxid 
Pure arsenic oxid 
Commercial zinc arsenite 
Commercial acid lead arsenate (new 
process) 
Commercial acid lead arsenate 
Commercial calcium arsenate 
....do 
do 
.....do 
....do 
....do 
Laboratory calcium arsenate 
Laboratory calcium meta-arsenate 
Laboratory monocalcium arsenate 
Laboratory sodium arsenate plus Bor- 
deaux mixture 
Commercial Paris green 
Commercial magnesium arsenate 
Laboratory barium arsenate 
Laboratory copper barium arsenate 
Laboratory aluminum arsenate 
Control with food 
1,184 
1,939 
1,361 
1,529 
1,516 
1,441 
422 
2,263 
2,645 
2,492 
2,373 
2,393 
2,114 
2,657 
2,298 
1,232 
1,758 
2,674 
2,059 
1,651 
1,706 
1,814 
1,482 
sftl 
...do 
...do 
...do 
...do 
...do 
sfl.... 
sftlg. 
...do. 
...do. 
...do. 
...do. 
...do. 
...do. 
...do. 
ft.... 
...do. 
"HE: 
Per cent. 
1.15 
1.73 
.57 
17.77 
100.00 
1.25 
.69 
.61 
.41 
.88 
1.31 
.20 
.52 
5.20 
.88 
.04 
89.26 
...do. 
..do. 
fly-. 
3.52 
4.64 
.68 
6.27 
1.91 
Per cent. 
21.5 
60.9 
59.6 
46.1 
76.5 
6S.9 
70.0 
39.9 
59.2 
60.1 
43.1 
65.9 
52.5 
3.6 
81.2 
61.7 
65.5 
50.2 
43.6 
48.9 
39.3 
Units. 
6S.6 
10.9 
17.6 
9.6 
3.5 
22.0 
2.8 
2.9 
9.1 
66.0 
30.8 
29.9 
68.1 
18.5 
55.0 
99.9 
2.0 
5.0 
3.2 
18.3 
22 2 
15^6 
16.1 
100.0 
l s, silkworms; f, webworms (H. cunea); t, tent caterpillars; 1, potato-beetle larvse; 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 study 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 
tor 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 3 calcium arsenates (samples 5, 
