4 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE. 
All samples of commercial arsenic acid are likely to contain traces 
of arsenious oxid and nitric acid. Arsenic acid solutions containing 
from 56 to 66 per cent of arsenic oxid have a specific gravity of from 
1.8 to 2. Solid arsenic acid containing from 75 to 80 per cent of 
arsenic oxid has recently been placed on the market. 
BASES USED IN PREPARING ARSENICALS. 
The oxids of lead, zinc, calcium, and magnesium are the bases 
most used in manufacturing arsenicals. Litharge is the commercial 
lead oxid and lime the commercial calcium oxid. Zinc oxid (ZnO) 
and lead oxid (PbO), ordinarily employed in the manufacture of zinc 
arsenite and lead arsenate, are more expensive than calcium oxid 
(CaO) (in the form of lime) and magnesium oxid (MgO) used in manu- 
facturing calcium arsenate and magnesium arsenate. Table 2 gives 
the results of the analyses of the five bases and the copper oxid 
(CuO) and barium hydroxid (Ba(OH) 2 ) which were used in this 
investigation. 
Table 2. — Composition of bases in arsenicals. 
Sample 
No. 
Material analyzed. 
Moisture, 
Oxid. 
Carbon 
dioxid 
(COa). 
Undeter- 
mined 
material, 
by dif- 
ference. 
Lime (laboratory) 
Lead oxid (laboratory) 
Lead oxid (commercial) 
Zinc oxid (commercial) 
Magnesium oxid (laboratory). 
Copper oxid (laboratory) 
Barium hydroxid (laboratory) 
Per cent. 
6.54 
.00 
.02 
.17 
.99 
.00 
14.58 
Per cent. 
Per cent. 
84.00 (CaO) 
9.02 
99.13 (PbO) 
Trace. 
97.88 (PbO) 
1.64 
lCO.OO(ZnO) 
.00 
77.16 (MgO) 
21.89 
98.75 (CuO) 
.10 
66.73 (BaO) 
14.91 
Per cent. 
0.44 
.87 
1.15 
3.78 
ACID LEAD ARSENATES. 
F. C. Moulton, chemist for the Massachusetts g} r psy moth com- 
mittee, is credited with the discovery in 1892 of the insecticidal 
properties of lead arsenate. The use of arsenate of lead as an in- 
secticide, first recommended in October, 1893 (21), has greatly 
increased during the past few years. Forty-two United States patents 
relating to its production have been issued. 
The principal lead arsenate is acid lead arsenate (PbliAsOJ, an 
acid salt, so-called because of the presence of hydrogen (H) in its 
molecule. It has the following theoretical composition, As 2 5 
(33.13 per cent), PbO (64.29 per cent), and water of constitution 
(2.58 per cent). 
In the early procedure for preparing acid lead arsenate, solutions of 
lead acetate or of lead nitrate were precipitated by sodium hydrogen 
arsenate (NaoHAsOJ. The tendency is to produce acid lead arsenate 
when lead nitrate is used and the more basic form when the acetate 
is used. McDonnell and Smith (27) obtained acid lead arsenate of 
practically theoretical composition by precipitating lead nitrate or 
lead acetate by an excess of monopotassium arsenate. A method 
frequently employed in manufacturing this arsenate is to mix arsenic 
acid (H 3 As0 4 ) and litharge (PbO) in the presence of a small amount 
of nitric acid. Other processes, however, are used. The fact that 
acid lead arsenate is a comparatively stable compound and is but 
