-67-
AECD-3446
k and the digestion flask washed with dilute hydrochloric acid and the washings
ed to the solution, Total volume about 50 ml.
VENGING
i
ProcedureI
Ten milligrams of arsenic as Aso0, was added and the solution was heated
immost to0 boiling and saturated with H,S.
Ee . to methyl red,
The precipitate of As,S-. was removed
One ml excess of conc.
NH,OH was added, the solution
:s heated almost to boiling, cooled, and the Fe(OH), removed by centrifuging
d transferred to a counting disk.
Ten milligramsof Fe’'* was added and the
gt HCl using methyl red indicator,. one ml more of HCl was added, the solution
“was heated almost to boiling and, while hot, 10 ml of ammonium oxalate solution
{0 g. per liter) was added dropwise, then ammonium hydroxide 1:5 was added
. "Gopwise from a burette to the hot solution until alkaline to methyl red.
The solu-
zton was allowed to stand on a hot plate for one hour and the precipitate of calcium
oxalate was removed by centrifuging and washed with 0.1% ammonium oxalate
lution made slightly alkaline with a few drops of NH4OH.
The CaC 2° 4° H,0 was
a fransferred to a counting disk and weighed.
.
After counting, the calcium oxalate was dissolved in dilute HCl, 1:4,
ited to 50 ml, one ml of 4% ammonium oxalate solution was added and the
falctum oxalate was again precipitated by treating with NH40H as above.
The
-“solution stood for one hour on the hot plate after which the precipitate was
= by centrifuging, w
\ ashed until chloride free with water to which a few
a8ml erlenmeyer flask, diluted to about 50 ml, heated to 80°C and titrated while
\ it with standard potassium permanganate solution.
.
The solution after titration was neutralized with NH40H, acidified with HCl,
‘ mg of Fe**” was added, and the solution was neutralized with NH40H; one ml
.
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i
C4
UNino & 4
On
te