Journal of Agricultural Research 
Vol. XXIV, No. 6 
518 
TabIv^ VII.— Apple and tomato sprayed with soluble arsenical compounds in amounts to 
contain 7.5 gm, of arsenic in 2 liters of solution 
Injury. 
Chemical. 
Apple. 
Tomato. 
Acid, arsenic. 
Acid, cacodylic. 
Ammonium arsenate. 
Potassium arsenate... 
Potassium arsenite... 
Potassium cacodylate 
Sodium arsenate. 
Sodium arsenite. 
Sodium cacodylate... 
Very bad. 
Defoliated. 
Partly defoliated 
Bad. 
Partly defoliated 
Defoliated. 
Moderate. 
Partly defoliated 
Defoliated. 
Very bad. 
Partly defoliated. 
Very bad. 
Bad. 
Very bad. 
Partly defoliated. 
Bad. 
Very bad. 
Nearly defoliated. 
Cacodylic acid and the cacodylates probably never occur in insecticides 
and are too expensive to be used as weed killers, and are therefore of more 
theoretical than practical interest. The scientific interest which they 
have in this connection lies chiefly in their very high toxicity to higher 
plant life and relative low toxicity to higher animal life. Cushny (d) 
states: 
The action being due to the ion and not to the element . . . organic arsenic combi¬ 
nations in which the metallic atom is directly attached to the carbon atom are only 
feebly poisonous. The earliest of these is sodium cacodylate, (CH3)2AsOONa. 
Merck's Index {20) states also : 
The cacodylates (which see) are now largely used instead of the alkali arsenites, as 
the former are far less toxic. 
It has been stated on high authority {23) that— 
Arsenious acid is extremely poisonous, whereas many, both of higher and of the lower 
plants, can withstand large doses of arsenic acid and can accumulate large quantities 
of arsenic when supplied to them in this form. 
This statement, while perhaps true under some conditions, is wholly 
misleading if applied to spray mixtures. 
NEARLY INSOI,UBD]e ARSKNICAD COMPOUNDS 
Turning to the arsenical compounds that are but slightly soluble, we 
find the comparison more difiicult. In the first place it is hard to get 
these chemicals that are pure and of definite composition, and in some 
instances they are not fully named. For example, a “lead arsenate" 
may be diplumbic ortho-lead arsenate or triplumbic ortho-lead arsenate 
or a mixture of the two, and neither the label nor the statement of the 
manufacturers reveals which of the three it is. Indeed, it is doubtful if 
an absolutely pure diplumbic or triplumbic lead arsenate is now on the 
market. Then, too, some of these chemicals are so slightly injurious that 
they cause no injury except under such conditions as will permit the 
more injurious ones to nearly or quite defoliate the plants or branches, 
making fine comparisons difficult. Furthermore, the number of chemi¬ 
cals in this group is so large, especially if we use several brands of the 
more important ones, that no single series of comparative tests is likely 
to be reliable throughout, owing to individual differences in the plants 
used, unless several are sprayed at the same time with each mixture, 
