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INSECTICIDES FOR EXTERNAL BITING INSECTS (FOOD POISONS). 
THE ARSENICALS: PARIS GREEN AND LONDON PURPLE, 
The arsenical compounds have supplanted all other substances for 
the insects falling under this heading. Two compounds are in common 
use, viz, Paris green and London purple.'| The use of powdered white 
arsenic is not recommended, on account of its greater liability to scald 
foliage and because it is very apt to be mistaken for harmless sub- 
stances. Of the first two mentioned, Paris green is the stronger insecti- 
cide, acting quickly, and is less liable to burn foliage. London purple 
has the advantage ot cheapness, and, being more finely powdered, is 
kept more easily suspended in water. The former can be had in 
14-pound or larger cans at 20 cents per pound, and the latter at 10 
cents per pound by the barrel. 
HOW TO APPLY ARSENICALS, 
There are three principal methods of applying arsenicals. The wet 
method, which consists in using these poisons in water in the form of 
spray, is the standard means, secures uniform results at least expense, 
and is the only practical method of protecting fruit and shade trees. 
The dry application of these poisons in the form of a powder, which is 
dusted over plants, is more popular as a means against the cotton 
worm in the South, where the rapidity of treatment possible by this 
method, and its cheapness, give it a value against this insect, in the 
practical treatment of which prompt and economical action are the 
essentials. This method is also feasible for any low-growing crop, such 
as the potato. The third method consists in the use of the arsenicals 
in the form of poisoned baits, and is particularly available for such 
insects as cutworms, wireworms, and local invasions of locusts. 


‘1A third arsenical which promises well, arsenate of lead, has lately been experi- 
mented with by the Gypsy Moth Commission. While not urging that this insecti- 
cide has advantages over Paris green, it is held that it has the merit of showing on 
the leaves, indicating at once which have been sprayed, remains much more easily 
suspended in water, and may be used in large proportions without danger to foliage. 
It has recently been extensively tested at the Department, and a strength as great 
as 1 pound to 2 gallons of water has been used on tender foliage of the peach and 
Osage.orange without injury. Good results have attended its use also against the 
unported elm leaf-beetle. The insecticide results were not better, however, than 
with Paris green ; but for such sensitive foliage as that of the peach, or where no 
risk of scalding may be taken, I am inclined to*believe that it will prove useful. 
This imsecticide is prepared by combining, approximately, 3 parts of arsenate of 
soda with 7 parts of acetate of lead. These substances unite chemically and forma 
fine, white powder which remains easily in suspension. As now used by the Com- 
mission, 10 pounds of the arsenate of lead are used with 150 gallons of water, 2 
quarts of glucose being added to cause the insecticide to adhere longer to the leaves. 
Professor Fernald’s experience and our own would indicate that from one-fourth to 
one-half this strength will answer for most larvee—the larve of the gypsy moth 
proving to be unusually resistant to the action of poisons. The arsenate of lead 
costs the commission 7 cents a pound wholesale, and glucose $16 a barrel. 

