24 BULLETIN 1147, U. S. DEPARTIMEXT OE AGRICULTURE. 
COMPARATIVE TOXICITY OF ARSENICALS. 
RESULTS OF PREVIOUS INVES IIGATIONS. 
CALCIUM ARSENATE. 
Bedford and Pickering (3) and Smith. (4S) appear to have been 
the first to use calcium arsenate as an insecticide. In 1907 all three 
of these men tried it as a substitute for lead arsenate. Bedford and 
Pickering found it practically as efficient as acid lead arsenate on 
fruit trees in England. Against the army worm in New Jersey, 
however. Smith did not find it satisfactory. 
Between 1907 and 1912, calcium arsenate apparently was not 
further tested as an insecticide, but during the seasons of 1912, 1913, 
and 1914, the office of fruit insect investigations of the Bureau of 
Entomology, United States Department of Agriculture, began to 
test it, as a result of which a commercial calcium arsenate was put 
on the market. Since 1915 the use of this arsenate in the field has 
steadily increased. In 1914 a commercial calcium arsenate in com- 
bination with lime-sulphur gave very satisfactory control of the 
codling moth (4&). 
Scott Ufi), who, during the seasons of 1913 and 1914, used calcium 
arsenate, states that for spraving apple and shade trees, it may be 
used with the same degree of efficiency and safety as acid lead ar- 
senate. 
Sanders (40), using acid lead and calcium arsenates of equal ar- 
senic contents, found the lead salt slightly superior in killing power, 
but the calcium salt more desirable for use with sulphid sprays. 
Sanders and Kelsall (#£) state that when calcium arsenate is 
used alone it may under some conditions burn foliage, but that when 
used in combination sprays with Bordeaux mixture or lime-sulphur, 
it is as safe as any known arsenical. In sodium sulphid sprays it 
is much the safest of all arsenicals. It adheres fairly well to foliage 
and remains in suspension. 
Coad (9) used various arsenicals, as dusts, against cotton boll 
weevils. He found acid lead arsenate much more toxic than basic 
lead arsenate and a high-grade calcium arsenate still more effective. 
Coad and Cassidy (10 and 11) recommend a high-grade calcium 
arsenate above all other arsenicals for controlling the cotton boll 
weevil, and they enumerate some of the physical and chemical prop- 
erties that such an arsenical should have. 
Eicker (33), testing poison baits against grasshoppers, determined 
that calcium arsenate, used in direct competition with Paris green 
and crude arsenious oxid, gave equally good results. 
BARIUM ARSENATE. 
Barium arsenate seems to have been used first by Kirkland (20), 
who tested it in Massachusetts against the larvae of the gypsy moth, 
fall webworm, and Datana ministra, securing satisfactory results in 
each case. Kirkland and Burgess {21) say: 
The experiments with barium arsenate in 1S96 gave so good results that we were 
hopeful that this insecticide would prove superior to lead arsenate. Its killing effects 
on larvae in confinement are certainly superior to those of arsenate of lead. In the 
field spraying operations it was found that the poison did not adhere to the foliage 
for a sufficiently long time to kill the larvae. 
