CHEMICAL CHANGES IN CALCIUM ARSENATE. a. 
may be present as impurities.”’ The results presented are not 
sufficient to substantiate this conclusion in so far as it applies to 
deterioration during storage. 
RESULTS OF PRESENT INVESTIGATION. 
The United States Department of Agriculture recommends the 
application of calcium arsenate on cotton only in the form of a dust. 
All of the work here reported, therefore, was done on calcium arsenate 
in the dry powdered form. 
It was realized that if chemical changes occur in calcium arsenate 
during storage, the type of container in which it is stored, as well as 
the original composition of the material and the climatic conditions 
under which it is stored might have an influence on the rate of this 
change. The plan as outlined therefore was to obtain material 
representing all of the leading commercial brands on the market and 
all of the principal types of commercial containers. Two original 
containers of calcium arsenate from six of the largest manufacturers 
of this material were stored in a frame warehouse at the Delta Lab- 
oratory of the Bureau of Entomology at Tallulah, La. One con- 
tainer of each of these six brands was put in storage intact and dis- 
turbed only at stated intervals when samples for analysis were drawn. 
The material in the other six packages was subdivided, 25-pound 
portions in each case being put into various standard types of con- 
tainers and the remaining material, from 50 to 100 pounds, retained 
in the original container. Four other samples, three of which repre- 
sented brands included in the six just mentioned, were placed in 
storage in the building occupied by the Insecticide and Fungicide 
Board (220 Thirteenth Street SW, Washington, D.C.). These were 
not subdivided. Samples were drawn at intervals from all of these 
containers for analysis.® 
The following scheme of marking for the identification of the vari- 
ous brands of calcium arsenate, the place of storage, and the kind 
of container, was adopted: Brands or manufacturers, A, B, C, F, H, 
I, and J; material stored in Washington, W, immediately after the 
letter designating the manufacturer; material stored in Tallulah, in 
original containers and without subdivision, 7; sets that were sub- 
divided and used for the container tests, S. All subdivisions were 
stored at Tallulah. 
COMPOSITION OF ORIGINAL SAMPLES. 
The results of the analyses of the samples made at the time of 
collection are given in Table 1. 
6 In sampling the material was disturbed as little as possible. Several cores were taken by means ofa 
trier, about 1} inches in diameter, at various places and extending at different angles from the top of the 
package to the bottom. The head of the container was immediately replaced, or the holes through which 
the trier was inserted were tightly closed. 
