ARSENICALS. 5 
slightly soluble in water, offers an explanation as to why it burns 
foliage only very slightly when properly applied. McDonnell and 
Graham (26) found that long-continued exposure to constantly 
changing water brings about decomposition, both lead and arsenic 
being dissolved, the arsenic, however, at a relatively greater rate, 
leaving the residue more basic than the original acid lead arsenate. 
According to McDonnell and Smith (27), the specific gravity of acid 
lead arsenate crystals is 6.05. 
The chemical data on 10 samples of powdered lead arsenates and 
on 9 samples of paste lead arsenate, the latter being dried in the 
laboratory before analysis, are reported in Table 3. Of the powdered 
arsenate samples 1 apparently was a basic lead arsenate and 9 were 
acid lead arsenates. Of the paste lead arsenate samples, 1 appar- 
ently was a basic lead arsenate and 8 were acid lead arsenates. These 
samples, which were obtained from various manufacturers in this 
country, include most of the leading brands. The results of the 
analyses, therefore, are representative of the composition of the 
commercial lead arsenates on the market in 1916. 
Table 3. — Composition of powdered and paste commercial lead and calcium arsenates. 
Sample 
No. 
Material analyzed. 
Mois- 
ture. 
Arsenic oxid 
(As 2 5 ). 
Oxid. 
Carbon 
dioxid 
(C0 2 ). 
Water of 
constitu- 
tion and 
Total. 
Water- 
soluble. 
impuri- 
ties by 
differ- 
ence.' 
1 
2 
13 
Powdered acid lead arsenate 
do 
do 
"""do"""!!"!"""".*'""! 
do 
do 
Percent. 
0.32 
1.43 
.21 
.17 
.30 
.14 
.20 
2.06 
.45 
.35 
.10 
.12 
.19 
.11 
.11 
.11 
.22 
.12 
.11 
.28 
1.58 
1.33 
.31 
9.56 
7.71 
11.30 
.99 
6.07 
Percent. 
30.86 
31.55 
32.29 
32.00 
31.24 
32.47 
32.93 
32.76 
31.59 
24.80 
31. 95 
32.30 
30.38 
32.07 
33.17 
32.51 
33.09 
32. 9S 
23.00 
43.35 
43.35 
49.40 
41.82 
38.16 
39.19 
40.49 
47.83 
45.37 
Percent. 
0.31 
.24 
.32 
.30 
.38 
.45 
.67 
.45 
.22 
.43 
.34 
.42 
.53 
.11 
.22 
.22 
.67 
1.73 
.50 
.70 
.38 
2.74 
.22 
1.92 
.55 
.08 
.25 
2.32 
Per cent. 
64.88 (PbO) 
62.95 (PbO) 
64.23 (PbO) 
63.42 (PbO) 
64.35 (PbO) 
64.29 (PbO) 
63.92 (PbO) 
63.70 (PbO) 
63.00 (PbO) 
72.23 (PbO) 
64.57 (PbO) 
64.50 (PbO) 
65.21 (PbO) 
65.01 (PbO) 
63.82 (PbO) 
64.67 (PbO) 
63.41 (PbO) 
63.13 (PbO) 
73.99 (PbO) 
38.86 (CaO) 
44.08 (CaO) 
40.57 (CaO) 
42.61 (CaO) 
37.38 (CaO) 
42.79 (CaO) 
44.03 (CaO) 
46.16 (CaO) 
41.48 (CaO) 
Per cent. 
0.54 
.15 
Percent. 
3.40 
3.92 
3.27 
14 
4.41 
35 
4.11 
38 
3.10 
39 
2.95 
40 
do 
1.48 
70 
do 
4.96 
28 
Powdered basic lead arsenate. . . 
Paste acid lead arsenate, dried. . 
do 
2.62 
3 
4 
Trace. 
3.38 
3.08 
29 
do 
do 
do 
do 
! ! ! ! !do !"!!!!!!!!!!!!!!!!!!!!!! ! 
4.22 
43 
2.81 
44 
2.90 
47 
2.71 
48 
3.28 
49 
3.77 
21 
Paste basic lead arsenate, dried. 
Paste calcium arsenate, dried.. 
Powdered calcium arsenate 
do 
do 
do 
do 
do 
do 
do 
2.90 
6 
7 
24 
32 
34 
56 
57 
58 
59 
2.74 
1.83 
.98 
1.64 
4.34 
4.04 
1.05 
1.70 
2.43 
14.77 
9.16 
7.72 
13.62 
10.56 
6.27 
3.13 
3.32 
4.65 
The results in Table 3 show that in most cases the chemical com- 
position of the commercial samples of acid lead arsenates closely 
approaches the theoretical composition. The manufacture of lead 
arsenate has become standardized to such an extent that different 
batches, or "runs, " of the product vary but little from the theoretical 
figures. Acid lead arsenates are sold in both dry and paste form, the 
paste containing usually from 45 to 50 per cent of water. 
