COMMERCIAL CALCIUM ARSENATE. 
Alter being mixed and standing for 15 to 20 minutes, the precipi- 
tates were filtered off and dried overnight on the steam bath. 
Portions were then sieved through a No. 100-mesh sieve, and their 
bulkiness was compared by measuring the volume occupied by 2.77 
grams in a 10-cubic centimeter graduated cylinder. Ten times the 
figure read on the cylinder is equivalent to the number of cubic 
inches per pound. The measurements were taken just as the material 
was poured into the cylinders, no attempt being made to pack it. 
Entomologists have stated that a good calcium arsenate for dusting 
purposes should occupy from 70 to 90 cubic inches per pound. 
Such determinations, however, are comparable only when conducted 
in the same way. 
The results of these experiments are summarized in Table 2. 
Table 2. — Effect of dilution and temperature on lightness of spraying compounds. 
Temperature. 
Degree of dilution and lightness of compound. 
Experi- 
A 
B 
C 
D 
No. 
11 gm. lime — 
35 cc. H 2 0. 
10 gm. As 2 5 — 
25 cc. H 2 0. 
11 gm. lime — 
70 cc. H 2 0. 
10 gm. As 2 6 — 
50 cc. H 2 0. 
11 gm. lime — 
105 cc. H 2 0. 
10 gm. AS2O5— 
75 cc. H 2 0. 
11 gm. lime — 
140 cc. H 2 0. 
10 gm. As 2 5 — 
100 cc. H 2 0. 
1 
Lime hot, acid 
Cu. in. per lb. 
60 
Cu. in. per lb. 
96 
Cu. in. per lb. 
104 
Cu. in. per lb. 
128 
2 
Acid hot, lime 
cold 
60 
104 
120 
112 
3 
Lime hot, acid 
hot 
60 
78 
92 
98 
4 
Lime cold, acid 
cold 
86 
104 
90 
80 
The general tendency is toward a production of lighter material in 
lower concentrations. But here a new feature, the hardness of the 
lumps and the effort necessary to reduce them to powder, makes its 
appearance. Amorphousness is usually associated with the produc- 
tion of hard, lumpy residues on drying, as, for example, in the case 
of aluminum hydroxid. So here 1 D, 2 C, and 2 D, the lightest of the 
powders, produce hard lumps, 2 D being the hardest of the lot. 
It was difficult to break them in the fingers, and for commercial use 
they would almost certainly have to be ground. On the other hand, 
4 A and 4 D were crumbly, and could be readily reduced to powder 
by shaking. Probably, then, a compromise between a method of 
preparation which produces the lightest powder and a method which 
produces the most easily pulverized powder would be necessary. 
Equal bulkiness is shown for 2 B, 4 B, and 1 C, all of which, espe- 
cially 1 C, were easily powdered. Based on this work, the authors 
believe that the most advantageous method to produce a reasonably light 
