ARSENICALS. 3 
used for insecticide purposes. Canada, Mexico, England, Germany, 
France, Japan, and Portugal produce large quantities of arsenious 
oxid. 
There are three forms of arsenious oxid : (a) The amorphous, vitreous, 
or glassy form; (b) the ordinary crystalline ("octahedral") form; and 
(c) the orthorhombic crystalline form. The amorphous form changes 
spontaneously into the crystalline form on standing. The trade 
usually recognizes two grades of arsenious oxid, the light and the 
heavy forms, although they are the same chemically. 
The literature contains conflicting statements concerning the 
solubility of arsenious oxid in water. Because of the slowness with 
which arsenious oxid goes into solution, many weeks being required 
to dissolve even a small sample of the solid, it is probable that in 
all of the reported results equilibrium had not been reached. The 
varying percentages of crystalline and amorphous material present 
in the samples tested, the amorphous form being more soluble than 
the crystalline forms, may possibly help to account for these dis- 
crepancies. 
With the exception of Paris green, the arsenites are prepared by 
combining arsenious oxid and the base. 
As a rule, arsenates are made by the direct action of arsenic acid 
in solution on a metallic oxid. The arsenic acid used for this purpose 
is manufactured from arsenious oxid by oxidation, usually by means 
of nitric acid, but sometimes by other oxidizing agents. 
The analytical results here reported are based on the weights of 
the original samples. The methods of analyses used were in general 
those of the Association of Official Agricultural Chemists (l). 3 
. Table 1 gives the analytical results on the six samples of arsenious 
and arsenic oxids selected to represent the arsenical materials used 
in the manufacture of arsenicals. 
Table 1. — Composition of arsenious oxid (As 2 O z ) and arsenic oxid (As 2 5 ) used in manu- 
facturing arsenicals. 
Sample 
No. 
Material analyzed. 
Moisture. 
Total 
arsen- 
ious oxid 
(As 2 3 ). 
Total 
arsenic 
oxid 
(As 2 5 ). 
Water- 
soluble 
arsen- 
ious oxid 
(As 2 3 ).i 
Water- 
soluble 
arsenic 
oxid 
(As 2 5 ).r 
9 
Laboratory arsenious oxid 
Per cent. 
0.20 
.99 
.71 
.15 
Per cent. 
99.80 
99.01 
99.29 
99.22 
Per cent. 
Per cent. 
17.77 
24.56 
38.00 
30.26 
Per cent. 
19 
Commercial arsenious oxid 
27 
do 
do 
Laboratory arsenic oxid (solid arsenic acid). 
Commercial arsenic oxid (dissolved arsenic 
37 
10 
77.27 
66.10 
77.27 
16 
66.10 
1 Determined by the A. O. A. C. method for Paris green. 
Attention is called to the wide variation in the data obtained for 
water-soluble arsenious oxid in the different samples of arsenious oxid. 
This is undoubtedly due to differences in the size and structure of 
the crystals present in the samples tested. 
Traces of arsenious oxid (0.008 per cent) and nitric acid (0.02 per 
cent) were found in the commercial sample of arsenic acid (No. 16). 
'Italic numbers in parentheses refer to literature cited. 
