30 
BULLETIN 1147, IT. S. DEPARTMENT OE AGRICULTURE. 
EELATIVE TOXICITY OF COMMERCIAL LEAD AND CALCIUM ARSENATES. 
\ 
Since the preliminary experiments indicated that the commercial 
acid lead arsenates do not differ greatly in toxicity, sample 39, one 
of those first used, was selected as a standard by which to judge the 
relative toxicity of other spray materials, because its arsenic oxid 
content (32.93 per cent) approaches most nearly the theoretical 
content (33.11 per cent). 
In order to obtain comparable percentages of toxicity for the three 
arsenates tested against five species of insects, it was first necessary 
to place all the daily percentages of mortalities on the same basis. 
This was accomplished by subtracting the daily mortalities of the 
control insects fed nonpoisoned food from the daily mortalities of 
the insects fed sprayed food. Since the daily mortalities on any 
given day vary too much to serve as a fair percentage of toxicity, 
the average of the mortalities on the third, sixth, and tenth days 
have been taken. The records given in Table 13 under the twentieth 
day show whether or not the insecticides used were efficient. To 
test the effect of starvation on the insects, other controls without 
food were used also. 
The results reported in Tables 13 to 21 are comparable only when 
the same combination of data and the same number of sets of insects 
have been used. Data on the number of sets tested and the varia- 
tion and average number of insects used for each individual spray 
material, other than those given in the tables, therefore, are stated. 
For Table 13 these data are as follows: Silkworms, 1 set (variation 
48-52, average 50); webworms (H. cunea), 2 sets (619-1224: 864); 
tent caterpillars, 4 sets (711-1126: 897); potato-beetle larvae, 3 sets 
(132-157: 145); and grasshoppers, 3 sets (368-482: 420). 
Table 13. — Relative toxicity of commercial lead and calcium arsenates on 5 species of 
insects, after deducting mortality of control with food, 1919 and 1920. " 
Arsenates and con- 
Percentage of insects dead within — 
3 days. 
6 days. 
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39 
Acid lead arsenate 
96.0 
39.1 
53.1 
61.5 
37.6 
57.5 
100.0 
91.7 
86.5 
72.3 
31.1 
76.3 
28 
Basic lead arsenate. . . 
61.3 
8.5 
53.6 
47.0 
33.0 
40.7 
81.6 
45.0 
88.5 
66.2 
31.6 
62.6 
5 
Calcium arsenate 
96.0 
12.5 
54.3 
67.5 
63.6 
58.8 
100.0 
69.1 
89.6 
66.9 
32.6 
71.6 
7 
do 
14.3 
3.6 
49.7 
45.6 
48.0 
32.2 
28.6 
15.6 
85.2 
47.0 
32.6 
41.8 
56 
do 
59.6 
4.3 
51.8 
54.8 
62.4 
46.6 
94.3 
33.7 
87.6 
54.9 
32.6 
60.6 
57 
do 
64.0 
1.1 
43.9 
60.5 
61.6 
46.2 
86.0 
27.8 
82.9 
73.3 
32.6 
60.5 
58 
do 
12.5 
2.7 
45.1 
50.6 
42.6 
30.7 
18.7 
18.7 
85.6 
70.4 
32.6 
45.2 
59 
do 
72.5 
3.8 
60.3 
57.8 
61.0 
51.1 
96.1 
42.1 
81.4 
60.8 
32.6 
62.6 
Control without food. . 
Control with food 
12.2 
.0 
.0 
.0 
.4 
1.9 
20.1 
14.6 
61.2 
.0 
28.6 
.7- 
15.3 
5.5 
43.7 
20.7 
35.5 
10.4 
67.4 
18.9 
