Apr. 7, 1923 
Action of Soap upon Lead Arsenates 
93 
Tabi^B III .—Quantity of As20^ that might be made soluble by the free {excess) sodium 
carbonate with stearate soap {4.72 per cent) 
No. 
Brand of 
lead arsen¬ 
ate. 
Weight of 
free 
Na2C03 
Equivalent 
weight of 
AssOo 
AS 2 O 5 
found in 
2 liters. 
Quantity 
due to 
soap (by 
difference). 
Total 
AsaOa in 
system. 
Arsenic 
made solu¬ 
ble by neu¬ 
tral soap. 
Gm. 
Gm. 
Gm. 
Gm. 
Gm. 
Per cent. 
I .. . .. 
0.0095 
0.0103 
0.1760 
0.1657 
0.3460 
47.89 
2. 
.0285 
.0309 
. 1870 
.1561 
.3460 
45.12 
3. 
.0095 
.0103 
.1424 
.1321 
.3460 
38.18 
4. •. .. 
“M” 
.0285 
.0309 
.1704 
•1397 
.3460 
40.37 
5 . 
it j > 
.0095 
.0103 
.0884 
.0781 
.2890 
27.02 
6. 
t{ f 
.0285 
.0309 
•0573 
.0264 
.2890 
9-13 
7. 
ft » 
.0095 
.0103 
.0670 
.0567 
.2890 
19.62 
8. 
<< > > 
.0285 
.0309 
.0572 
.0261 
.2890 
9.02 
17 . 
.0095 
.9103 
. 1280 
.1177 
.4050 
29.06 
18. 
“M” 
.0285 
.0309 
.2814 
•2505 
.4050 
61.85 
19 . 
.0095 
.0103 
•1325 
. 1222 
.4050 
30.17 
20. 
.0285 
.0309 
•3097 
.2788 
.4050 
68.84 
21. 
tt f 
.0095 
.0103 
.0625 
.0522 
.3090 
16.89 
22. 
it f 
.0285 
.0309 
. 1084 
•077s 
.3090 
25.08 
23 . 
1 (> > 
.0095 
.0103 
.0596 
.0493 
.3090 
15-95 
24 . . 
.0285 
.0309 
•089s 
.0586 
.3090 
18 96 
It is plain from Tables I, II, and III that “M” is very much more 
acted upon by both soaps than is “T” and that sodium stearate is very 
much more (two to seven times) effective in dissolving arsenic from lead 
arsenates than is sodium oleate. It follows that if it is desired to use 
soap with lead arsenate in spraying, the danger of injury from arsenic in 
solution can be diminished in some degree by securing triplumbic arsenate 
but could be almost entirely overcome by using only sodium oleate as 
the soap. 
It is also clear that sodium stearate at least does not act as stated by 
G. Ennis Smith (5), but dissolves arsenic from the basic arsenate and 
dissolves much more than the 40 per cent that should be made soluble 
in transforming diplumbic into lead hydroxy arsenate. This behavior is 
exactly in accord, however, with the supposition that the reaction is of 
the double decomposition sort, giving insoluble lead soaps as one of the 
end products, instead of free fatty acids as Smith states. In order to 
conffrm this supposition, the insoluble residues from the first series were 
analyzed for arsenic and for lead. 
In case the reaction stops as soon as the iead hydroxy arsenate is 
reached, the ratio of lead oxid to arsenic pentoxid could never be greater 
than that in the lead hydroxy arsenate, i to 3.23, and would usually be 
lower than that, as there would be some material unacted upon. On the 
other hand, if lie reaction is of the double decomposition sort, it might 
be possible to carry the reaction far beyond that ratio, as in fact occurs 
in six of the eight samples that were acted upon by sodium stearate. 
When oleate soap was used, the reaction was so incomplete that the ratio 
never approaches even i to 3. It may be that soap first transforms 
diplumbic arsenate into lead hydroxy arsenate and then undergoes a 
double decomposition with that salt, but it is hard to explain the results 
on the supposition that the action stops at the lead hydroxy arsenate. 
The results of the analysis of the dry insoluble residue and the ratio of 
AS2O5 to PbO are given in Table IV. 
30615—23-7 
