354 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 11 
CALCIUM ARSENITE AND ARSENATE AS INSECTICIDES 1 
By E. B. Holland, Associate Chemist , and J. P. Buckley, Assistant Chemist, 
Massachusetts Agricultural Experiment Station 
An intensive production of orchard and garden crops the present 
season will tend towards a maximum consumption of arsenicals in 
combating leaf-eating insects. A scarcity of lead arsenate, the stand¬ 
ard “stomach poison” insecticide, or a prevailing high price will 
undoubtedly bring into the market other cheaper and less reliable ar¬ 
senicals such as calcium arsenite and calcium arsenate. The acknowl¬ 
edged requisites for an insecticide that is to be applied as a spray are: 
non-toxicity as to plant, effectiveness in destroying the insect, adhesive¬ 
ness or persistence under weather conditions, fineness of particles and 
low specific gravity to insure a high power of suspension and uniform 
distribution, ability to indicate the leaf surface covered, and reasonable 
cost. All arsenical compounds are poisonous, although as a rule the 
lower or “ite” salts are more active than the higher or “ate” salts. 
Arsenic soluble in water or which has been rendered soluble by atmos¬ 
pheric agents has a corrosive (burning) action on foliage to the extent 
of entire defoliation of the plant in severe cases. Therefore an arseni¬ 
cal must be insoluble and stable in water or in whatever vehicle em¬ 
ployed to insure its safe application. 
Pure calcium arsenite, Ca(As0 2 )2, is a white powder, fairly soluble 
in water but practically insoluble in presence of excess lime, and con¬ 
tains 77.92 per cent arsenic trioxide. As a farm preparation it was 
formerly used considerably in the central and western portions of the 
United States, but recently it has appeared in eastern markets in the 
form of paste under a trade name. Some years ago Holland and 
Reed 2 prepared the pure salt and determined its formula and solubility. 
Spraying tests by the Department of Entomology of this institution 
showed that it is likely to cause some injury even when mixed with 
strong (3 per cent) milk of lime. Similar results might be expected 
when applied with Bordeaux. Calcium arsenite with excess lime has a 
good power of suspension, the white film readily indicates the leaf 
surface covered and its adhesiveness provides protection for a reason¬ 
able period under average weather conditions. Pure sodium arsenite 
is a white powder, very soluble in water and contains 76.15 per cent 
arsenic trioxide. Although offered on the market in solution under a 
1 From the Department of Chemistry, Massachusetts Agricultural Experiment 
Station. Printed with the permission of the Director of the Station. 
2 1912, The Chemistry of Arsenical Insecticides. > In Mass. Agr. Expt. Sta., Rpt. 
24, pp. 194-201. 
