May 12.1923 Injury to Foliage by Arsenical Spray Mixtures 
519 
making a series so large that the last must be applied much later than 
the &st. Table VIII will, however, give a nearly correct idea of their 
relative injuriousness. Under the conditions governing these experi¬ 
ments it should be constantly kept in mind that these results might be 
different if other brands of the chemicals were used or if climatic conditions 
were different. 
If we consider the results shown in this table and also those from many 
other spraying tests, we come to the conclusion that the order of injuri¬ 
ousness of the chemicals listed in Table VIII when sprayed on to foliage 
under our conditions is as follows : 
1. Calcium arsenite. 
2. Arsenic trisulphid, 
3. Barium arsenate. 
4. Calcium arsenate. 
5. Lead arsenite. 
6 . Copper aceto-arsenite. 
7. Arsenic disulphid. 
8. Arsenic trioxid. 
9. Zinc arsenite. 
10. Lead arsenate diplumbic. 
11. Lead arsenate triplumbic. 
12. Ferrous arsenate. 
Tabi.e VIII. —Results of spraying different plants with ** insoluble" arsenical compounds 
in such amounts as to give equal weight of arsenic to 2,000 cc. water to show relative 
toxicity 
Chemical. 
Injury to bean, 
May 3, 1915 (i 
gram arsenic in 
2 liters of water). 
Injury to apple, 
June 18, 1915 (2 
grams arsenic in 
2 liters of water). 
Injury to tomato. 
Aug. 14, 1916 (2 
grams arsenic in 
2 liters of water). 
Arsenic trioxid, Baker... 
Arsenic disulphid, Merck. 
Very slight.... 
.do.... 
None. 
.do. 
None. 
Do. 
Very bad. 
Bad. 
Moderate. 
Partly defo¬ 
liated. 
None. 
Do. 
Very slight. 
None. 
Do. 
None. 
Arsenic trisulphid. Baker. 
Barium arsenate, Adler. 
Calcium arsenate, Merck. 
Bad. 
Moderate. 
.do. 
Slight. 
Moderate. 
....do. 
Calcium arsenite, Baker. 
Ferrous arsenate, Merck. 
Lead arsenate, diplumbic. Baker... 
Lead arsenite, Merck. 
Defoliated. 
Very slight.... 
Partly defo¬ 
liated. 
None. 
.do. 
Lead arsenate, triplumbic. Baker. . 
Paris green. Baker. 
Zinc arsenite, “Ortho 40”. 
None. 
Moderate. 
Very slight.... 
Moderate. 
Slight. 
Probably the most striking fact brought out by this phase of the work 
is that arsenic trioxid may be applied with so little injury. It is well 
known that this compound has been kept out of general use by the injury 
it has caused under field and orchard conditions in other localities. We 
have sprayed both apple and several herbaceous plants many times and 
on many dates during a period of several years and have never found it 
especially injurious if the mixture was applied as soon as prepared. This 
might not be true in localities with a high humidity. Even the freshly 
prepared amorphous form which is more soluble than the crystalline form 
has given less injury than the majority of the slightly soluble arsenical 
