58 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 11 
foliage. This same difficulty was encountered in the earlier attempts 
to use lead arsenate and it was therefore assumed that, as with the 
latter, a more complete knowledge of the properties of calcium ar¬ 
senate, its composition and preparation, might lead to some practical 
method for its substitution for the more expensive lead arsenates. 
The calcium arsenates which would prove of any practical interest 
from an insecticidal point of view must have certain physical and 
chemical properties, including a reasonable stability. A study of the 
commercial calcium arsenates, including some supposedly high grade 
c.p. salts intended for reagents, indicated that without exception they 
were mixtures of two or more calcium salts, no two of which were alike 
in composition. 
Believing that the only possible method to properly study the proper¬ 
ties of the calcium arsenates for the purpose of determining their value 
as an insecticide and to establish any reliable data from which sound 
conclusions may be drawn as a basis for future work is to prepare the 
pure salts, this study was first undertaken. 
Calcium Arsenates Prepared 
The chemical work in connection with this project was outlined and 
developed in its entirety by Mr. R. H. Robinson, Assistant Chemist at 
the Oregon Station, and a manuscript detailing the work and results 
has been submitted to the Journal of Agricultural Research. This will 
be published probably in April and to comply with the spirit and letter 
of the regulations concerning matters submitted there, an attempt will 
be made simply to summarize some of the essential details of this work. 
Two calcium salts, the acid calcium arsenate and the neutral or basic 
calcium arsenate, known respectively as CaHAs0 4 and Ca 3 (As0 4 ) 2 
were prepared in the pure form, both of which give much promise as 
insecticides. The chemical and physical properties of the two salts, 
including the specific gravity, solubility and relative stability were 
determined. The specific gravity and fineness of division, physical 
properties so essential in a powdered spray to permit of the efficient 
spread on foliage and a suspension for a reasonable time in solution, 
were found to be satisfactory. Both materials when subjected to severe 
tests were found to be somewhat soluble. The calcium hydrogen or 
acid arsenate is decidedly soluble, approximating the amount shown 
by field tests to cause serious burning and indicating that this salt 
should not be used alone as a spray. The tricalcium, neutral or basic 
arsenate is only slightly soluble and would appear to be a safe spray 
material to use alone. From the standpoint of stability, the basic 
arsenate again showed to an advantage while the acid arsenate proved 
very unstable, permitting the formation of harmful amounts of soluble 
arsenic. 
