ARSENICALS. 
31 
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 — Continued. 
Percentage of insects dead within — 
10 days. 
20 days. 
sis 
A 
ffi 
i 
3 
% 
ago 
T5 C3-0 
IS9 
6 
Arsenates and con- 
trols. 
i 
| 
33 
a 
> 
1 
1 
! 
to 
i 
CO 
a 
a 
ft 
5 
t 
>-> 
•3 
1 
ft 
s 
02 
I? 
1 
En 
6 
o 
bo 
El 
o 
02 
1? 

s 
6 
03 
"S 
Ph 
3 
Pi 
|I1 
39 
Acid lead arsenate 
84.5 
87.3 
52.5 
All. 
81.1 
AU. 
AU. 
All. 
71.6 
2.9 
28 
Basic lead arsenate. . . 
9*6.6 
74.8 
87.5 
47.0 
Ail. 
76.3 
100.0 
AU. 
AU. 
All. 
59.9 
10.9 
fi 
f!a.icinm arsenate 
84.0 
24.4 
87.7 
87.7 
53.7 
40.6 
Ail. 
All. 
81.3 
45.8 
"44." 9' 
AU. 
20.7 
AU. 
All. 
AU. 
All. 
70.6 
39.9 
9.1 
7 
do 
30.3 
66.0 
56 
do 
98.1 
52.4 
86.8 
43.8 
All. 
70.3 
100.0 
49.8 
AU. 
All. 
59.2 
30.8 
57 
do 
98.0 
50.3 
84.7 
51.5 
All. 
71.1 
100.0 
45.7 
AU. 
AU. 
59.3 
29.9 
58 
do 
22.9 
22.2 
87.7 
53.2 
All. 
46.5 
29.2 
20.5 
AU. 
All. 
40.8 
69.1 
59 
do 
100.0 
69.4 
86.6 
52.3 
All. 
77.1 
51.9 
AU. 
AU. 
63.6 
18.5 
Control without food. . 
Control with food 
71.5 
.0 
83.3 
14.4 
79.3 
12.3 
37.4 
42.5 
100.0 
0.0 
All. 
41.8 
AU. 
50.5 
34.0 
57.1 
"15.5" 
78.3 
17.3 
100.0 
Table 13 shows the following: The average percentages of toxicity 
of the acid lead arsenate (sample 39) and of one sample of calcium 
arsenate (sample 5) on five species of insects are practically the same; 
the percentage of toxicity for another calcium arsenate spray (sample 
59) is a little lower; those for two other calcium arsenates (samples 
56 and 57) and for basic lead arsenate (sample 28) are practically 
the same; while those for the remaining calcium arsenates (samples 
7 and 58) are very low. Samples 7 and 58 were not efficient against 
all five species of insects tested. The basic lead arsenate acted much 
more slowly on the silkworms and webworms than did the acid lead 
arsenate, but, as a rule, only slightly more slowly on the tent cater- 
pillars, potato-beetle larvae, and grasshoppers. The quantity of food 
consumed is inversely proportional to the toxicity, being least for 
samples 39 and 5 and most for samples 58 and 7. The results in 
this table also show that starvation had little or no effect on the in- 
sects tested, but that the insects really died from the effects of the 
arsenates. 
EFFECT ON TOXICITY OF ADDING LIME TO ARSENICALS. 
According to the preliminary experiments conducted in 1917 and 
1918, the laboratory sample of calcium arsenate (sample 42) and the 
same compound plus 0.3 gram of lime (sample 42A) killed 69 per cent 
and 68 per cent, respectively, of the webworms counted on the 
twelfth day. When the quantity of lime was doubled (sample 42B) 
the mortality was 50 per cent, and when it was quadrupled (sample 
42C), 40 per cent. In 1919 many other experiments, in which a 
larger amount of lime was added to every 418 cubic centimeters of 
another laboratory sample of calcium arsenate, were performed, using 
silkworms, 1 set (variation 49-53, average 51) ; webworms (H. cunea), 
2 sets (538-818: 622) ; tent caterpillars, 4 sets (785-1021 : 943) ; web- 
worms (H. textor), 1 set (181-325: 266); potato-beetle larvae, 3 sets 
(290-361:339); and potato-beetle adults, 1 set (37-41:39). De- 
