May 12,1923 lujuTy to FoUage by Arsenical Spray Mixtures 
527 
in solution would be less than if allowed to stand for some time and the 
injury correspondingly less. To what extent this principle will operate 
can be determined by experiment only. 
To this end we have made repeated trials with arsenic trioxide and a 
few with calcium arsenite, calcium arsenate, lead arsenate, and Paris 
green. 
Quite without exception the burning by arsenic trioxide steadily 
increased as the mixture was allowed to stand. Table XVI illustrates 
a typical demonstration of this fact. In this case suspensions of arsenic 
trioxide^^ (2.6 gm. in 2 liters) were prepared at different intervals so 
spaced that all would be ready for spra)dng at the same time, having stood 
the time periods indicated in the left hand column of the table. These 
suspensions after mixing were kept in an incubator at blood temperature 
and were stirred at intervals of about six hours, day and night. At the 
time of spraying the suspensions were thoroughly shaken and a small 
sample removed and filtered through Swedish filter paper, and the 
filtrate analyzed. The remainder was sprayed upon tomato and bean 
plants in triplicate. 
TabIv® XVI .—Effects of letting arsenic trioxid stand after mixing 
Time after mixinsr. 
Arsenic trioxid 
Injury. 
in solution. 
Bean. 
Tomato. 
5 minutes. 
Per cent, 
0. 001392 
. 002784 
. 006960 
. 012520 
. 016720 
. 024128 
. 032480 
Slight. 
None. 
I hour. 
Moderate. 
Do. 
2 hours. 
Very bad.. 
Slight. 
Moderate. 
4 hours. . . 
Defoliated. 
8 hours... 
.do. 
Do. 
12 hours. 
.do. 
Bad. 
24 hours. 
Dead.. 
Very bad. 
Table XVI shows strikingly the progressive increase in burning by 
allowing arsenic trioxid to stand in suspension and the corresponding 
inarease in the amount of the chemical that went into solution. Other 
experiments showed that this increase in injury as a result of standing 
continued for at least 48 hours and was strongly in evidence whether or 
not soap was added to the mixture. Kilgore {14) has shown that arsenic 
trioxid suspended in water continues to dissolve for 10 days. 
The tendency of calcium arsenite, calcium arsenate, lead arsenate, 
and Paris green to increase in burning power as a result of standing in 
suspension is relatively slight. 
EFFECTS OF REPEATED SPRAYING 
It is often necessary for the control of insect pests to spray plants or 
trees two or more times at intervals of a few days or weeks, and in such 
cases it is important to know if the second or later applications are 
especially dangerous from the standpoint of injury to the foliage. Clinton 
and Britton {2) showed that the second application of zinc arsenite may 
do very serious damage, even though the fost did little or no harm. Our 
work with two brands of zinc arsenite, Thomson’s and Ortho 40,” 
13 Baker's. 
39363—23 - 7 
