522 
Journal of Agricultural Research 
Vol. XXIV, No. 6 
safe to use. Even with lime sulphur added calcium arsenite does more 
damage to the foliage than any other arsenical in the list given in Table IX. 
We have given some attention to finding an explanation for the re¬ 
duced injury by calcium arsenite when lime sulphur is added. As a 
principle of physical chemistry, the lime sulphur containing calcium 
sulphids, which are more readily soluble than calcium arsenite, would 
be expected to prevent to some extent the ionization of the less soluble 
salt. If this were the only consideration involved, other soluble calcium 
salts would be expected to have the same effect. To test this experi¬ 
mentally we added calcium nitrate to certain lots of calcium arsenite 
suspension, and calcium chlorid to other lots. These were sprayed upon 
tomato, bean, and cucumber plants in comparison with calcium arsenite 
alone and calcium nitrate and calcium chlorid alone. In almost every 
instance the injin-y was increased slightly by the addition of the nitrate 
and chlorid, though these compounds in themselves caused no injury. 
After repeated tests we decided that other factors than the restraint of 
ionization must enter in. This question is now receiving further study. 
TOBACCO J^XTRACT 
This insecticide has come into quite general use for the control of plant 
lice. It will often save the labor of one spraying application to combine 
it with an arsenical spray mixture. The results of such combination in 
injury to the foliage are shown in Table X. The conditions under which 
the tests there recorded were carried on as to dates, localities, arsenical 
chemicals, etc., are essentially as described on page 521. The tobacco 
extract is the “Black Leaf 40.“ It was used at the rate of 2.5 cc. to 
each 2 liters of water. 
It is evident from Table X that the effect of tobacco extract upon the 
injurious properties of the arsenical compounds is not marked. It is 
probable that we may safely state that it does not increase the injury 
with any of the arsenicals tested, to such an extent as to make its use 
undesirable and on the other hand it does not decrease the injury in any 
case enough to make this an important consideration. 
Tabl^ X.— Effects of tobacco extract on the burning properties of various arsenical 
compounds 
Arsenical compounds to which tobacco 
extract was added. 
Number 
of brands. 
Number 
of appli¬ 
cations. 
Number 
of times 
injury 
increased. 
Number 
of times 
injury 
decreased. 
Number 
of times 
injury 
was the 
same. 
Number 
of times 
there was 
no injury 
with or 
without 
the 
extract. 
Arsenic trioxids. 
2 
2 
0 
0 
I 
I 
Arsenic disulphid. 
I 
I 
I 
0 
0 
0 
Arsenic trisulphids. 
2 
4 
0 
I 
I 
2 
Barium arsenate. 
I 
2 
2 
0 
0 
0 
Calcium arsenites. 
3 
22 
3 
7 
9 
3 
Copper aceto arsenites. 
2 
20 
2 
6 
4 
8 
Ferrous arsenates. 
3 
15 
I 
0 
I 
13 
Lead arsenates, triplumbic.... 
7 
62 
3 
2 
0 
57 
Lead arsenates, diplumbic.... 
13 
97 
5 
3 
2 
87 
Lead arsenates, mixtures. 
10 
28 
2 
0 
0 
26 
Zinc arsenites. 
6 
52 
8 
3 
10 
31 
