BULLETIN 750, U. S. DEPARTMENT OF AGRICULTURE. 
erate rise in temperature occurs. For instance, in 4 A the tempera 
ture rose from 32°C. to 65°C, and in L D from 32°C. to 40°C. 
After mixing and standing for 15 to 20 minutes the precipitates 
were filtered off. and dried over night on the steam bath. Portions 
were then sieved through a No. 100 mesh sieve, and their bulkiness 
compared by measuring the volume occupied by 2.77 grams in a 10 
cubic centimeter graduated cylinder. Ten times the figure read <>n 
the cylinder equals 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. EnT'unologists have 
stated that a good calcium arsenate for dusting purposes should 
occupy from 70 to 00 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 i'. 
Table 2. — Effect of dilution and temperature on lightness of spraying com- 
pounds. 
•Temperature. 
Series number, degree of dilution, and lightne 
ss : mpound. 
A. 
B. C. 
D. 
ment 
Xo. 
11 
10 
-- 
gin. lime — ■ 
cc H 2 
gm. As,0 5 — 
ec H,0.~ 
11 gm. lime — 11 gm. lime — 
H 2 105 eo H 2 
10 gm. As 2 5 — 1C gm. As,0_— 
H,0. ' " HJOi 
11 gm. lime — 
140 ec H : «j 
10 gm. As_' "•.— 
100 ce ttjO. 
1 
Lime kot : acid 
cold 
c 
u. in. per lb. 
63 
. .. per lb. Cu.in.pt 
90 104 
128 
o 
Acid hot, lime 
cold 
•v: 
104 
112 
3 
Both hot 
63 
TS 92 
OS 
4 
Both cold 
SO 
104 90 
SO 
These results show that the general tendency is the production of 
the lighter material in the lower concentrations. But here a new 
feature, the hardness of the lumps and the effort necessary to reduce 
Them to powder, makes its appearance. Amorpkousness is usually 
associated with the production of hard, lumpy residues on drying. 
as, for example, in the case of aluminum hydroxid. So here we 
have 1 D, 2 C, and 2 D, the lightest of the powders, producing hard 
lumps, 2 D being the hardest of the lot. It was difficult to break 
Them in the lingers, and for commercial use they would almost cer- 
tainly have to he ground. On the other hand, 4 A and 4 D were 
crumbly, and could be readily reduced to powder by simply shaking 
them. Probably, then, a compromise between a method of prepara- 
tion which produces the lightest powder and a method which pro- 
duces the most easily pulverized powder would be necessary. 
