523 
May 12,1923 Injury to Foliage by Arsenical Spray Mixtures 
SOAP 
In spraying some plants, for example, cabbage, and to a less extent 
sugar beet, the spray mixture does not spread on the surface of the leaf 
and adhere, but rolls off in droplets, leaving most of the surface unpro¬ 
tected. It has been found that the addition of soap will nearly or quite 
obviate this. Furthermore, Parker {22) has shown that soap will very 
materially retard the settling of lead arsenate from its suspension in 
water. The natural tendency of soap to increase the solubility of the 
slightly soluble arsenical compounds is well recognized and the question 
arises, will this result in an increased tendency to injine the foliage on 
the part of some or all of the arsenical insecticides ? 
During this investigation several different kinds of soap were tried 
and several strengths were used, but in the tests recorded in Tables XI 
and XII one brand was used exclusively, 14.4 gm. being added to 
each 2 liters of spray mixture. The arsenical chemicals were the same 
in kind and strength as recorded on page.521. 
TabIvE XI .—Effects of soap on the burning properties of various insoluble'* arsenical 
compounds 
Arsenical compounds to which soap 
was added. 
Number 
of brands. 
Number 
of appli¬ 
cations. 
Number 
of times 
injury in¬ 
creased. 
Number 
of times 
injury de¬ 
creased. 
Number 
of times 
injury 
was the 
same. 
Number 
of times 
there was 
no injury 
with or 
without 
the soap. 
Arsenic trioxids. 
4 
lOS 
16 
7 
II 
Arsenic disulphids.. 
I 
14 
2 
0 
0 
12 
Arsenic trisulphids. 
2 
17 
9 
I 
3 
4 
Barium arsenates. 
I 
9 
4 
I 
4 
0 
Calcium arsenates. 
I 
77 
48 
6 
17 
6 
Calcium arsenites. 
3 
123 
27 
28 
63 
5 
Copper aceto arsenites. 
2 
123 
8 
64 
28 
23 
Ferrous arsenates. 
3 
29 
I 
0 
0 
28 
Lead arsenates, triplumbic.... 
8 
95 
13 
I 
0 
81 
Lead arsenates, diplumbic.... 
13 
140 
56 
0 
I 
83 
Lead arsenates, mixtures. 
10 
57 
19 
0 
0 
38 
Lead arsenite. 
I 
5 
4 
0 
0 
I 
Zinc arsenites. 
6 
90 
II 
10 
17 
52 
Table XI shows that of the “insoluble’^ arsenicals tested all but three 
cause greater injury if soap is added. This increased injury is most 
conspicuous in the lead arsenates. Of these, 8 brands were triplumbic, 
13 diplumbic, and 10 were probably mixtures of both. The increase of 
injury through the addition of soap is a little more pronounced wi^ the 
diplumbic than with the triplumbic arsenates, but the difference is not 
so great as some have supposed. 
One of the most surprising observations made in this phase of the 
investigation is the reduction in injury caused by copper aceto-arsenite 
when soap is added. , 
Not all brands of soap give the same results when combined with 
arsenical spray mixtures. Some appear to retard the injury by copper 
aceto-arsenite more than others, and they vary in the degree to which 
they increase the injury by lead arsenates and other compounds. Neither 
do they show equal power to keep lead arsenate in suspension. While 
“ Diamond C.’ 
