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THE DETERMINATION OF CADMIUM
AS CADMlUM PYROPHOSPHATE

Thesis for the Degree of M. S.
MICHIGAN STATE COLLEGE

George Jacob Atchison
1941

THE DETERMINATION OF CADHIUM A3
CADMIUM PYROPHOSPHATE

by
GEORGE JACOB ucnmou

A THESIS

Submitted to the Graduate School of lichigan
State College of Agriculture and Applied
Science 1n.pert1el fulfilment of the
requirements for the degree or

IASTER OF SCIENCE

Department of Chemistry
1941

‘ I
ll‘ll

 

7546.;

A <6 (03}

ACKNOWLEDGMENT
The writer wishes to express his sincere
appreciation to Ir. llner Leininger, Associate
Professor of Chemistry, for the able guidance
and helpful suggestions offered during the course
of this work.

\I

113%. / O

13

INDEX

Page
IntromJCtion e e e e e e e e e e e e e e 1
Historical . . . . O . O O . O . O . . . 2

Experimental............oo4

SWeeeeeeeeeeeeeeee25

Bibliography' .24

O
O
O
O
O
O
O
O
O
O
O
O
O

INTRODUCTIOI

The well known method of determining magnesium as
the pyrophosphate by igniting the precipitated magnesium
ammonium phosphate has been applied to the determination
‘ of cadmium but without a large measure of success. The
determination is time consuming and due to the solubility
of the cadmium amonium phosphate in both acidic and
basic solutions the results obtained are usually low.

As a consequence the method has never been popular.

The accepted procedures specify that the precipi-
tation is to be made in a neutral or faintly acid solution,
however none of the previous investigators has determined
the influence of the hydrogen-ion concentration on the
precipitation. The object of this investigation, there-
fore, was to find the effect of changing pH, to determine
the optimum pH for the precipitation, and to study the
precipitation of cadmium with diamonium hydrogen phos-
phate in solutions of controlled pH.

HISTORICAL

Austin (1) in 1899 investigated the double phos-
phate method of precipitation and applied it to zinc,
beryllium and cadmium. She made the precipitation by
adding hydrogen sodium amonium phosphate to the hot
solution containing the metal and then heating until
the precipitate became crystalline. Results obtained for
cachiium were good when the precipitation was made in the
presence of ten per cent of ammonium chloride with a
standing time of about sixteen hours before filtration.

Dakin (2) reported in 1900 that the presence of
large amounts of amonium chloride were uneceeeary for
accurate results. He also advocated the use of di:-
ammonium phosphate instead of the sodium compound as
eliminating the error due to the presence of sodium in
the precipitate. Another of Dakin's modifications was
the precipitation of the cadmium ammonium phosphate from
a cold rather than a bet solution since he found that
hot precipitation gave a product of deficient amonia
content.

tiller and Page (3) a year later verified Dakin's
method of cold precipitation and stipulated that for
accurate results the precipitation should take place in
a cold, neutral solution with a large excess of
diamonium phosphate and an overnight standing period
before filtration. Iinkler (4) reported in 1921 that

-3-
the presence of more than five grams of amonium chloride
in one hundred milliliters of solution produced low
results, and gave the ideal concentration of amonium
chloride as being two grams per one hundred milliliters
of solution.
lens of the investigators gave equations for the

reactions between the cadmium and the precipitating
reagent. Hillard a Furman (5) in their book 'llementery
Quantitative Analysis“ state that ”cadmium is precipi-
tated first as simple phosphate which later becomes the
crystalline double salt." The expected equations for
the reactions are:

30d012 + 2(NB4)28PO‘—s Cd3(P04)2 1’ 41111401 + 2301

“3004);; + (m4) 231,04 + m4c1—. wm‘PO4i'HG1

2cm4ro4-fl. «22207 + 21135 + 1120

summer.

a stock solution was prepared by dissolving 62.8
grams of 0.2. Odelz ° 2-1/2320 and ten milliliters of
concentrated c.P. hydrochloric acid in distilled water
and making up to roughly seven liters. This solution
was then used as a source of standard cadmium content.

To determine the cadmium content of the stock
solution twenty-five milliliter portions were standardized
by two methods, (a) by electrolytic deposition of the
cadmium upon platinum, and (b) as cadmium sulfate. For
the electrolytic determination the samples were treated
according to the cyanide method of Beilstein and Jawein
(6) as given by Hillebrand and nmdell. Platinum gauze
was used for the anode and for the cathode and the
solutions were tested for complete deposition after
electrolysis using hydrogen sulfide gas. For the deter-
mination as cadium sulfate the samples were evaporated
in platinum crucibles with an excess of sulfuric acid
and the excess acid carefully fumed off using a nickel
radiator. The residue was then ignited in an electric
muffle furnace by gradually raising the temperature to
five hundred degrees Centigrade and weighed as cadmium
sulfate. The residue was dissolved in a small volume
of water, carefully evaporated and ignited and this
procedure continued until constant weights were obtained.

Table I shows the results obtained by the two described

-5-

methods for samples from a pipette found to deliver 04.94

milliliters.

TABLE I

Standardization of the Cadmium Solution

 

 

 

 

 

3. 0d / 24.94 ml. soln.
is Electrolytic
(M804 Deposition
0 . 1033 0. 1038 =
0.1037 0. 1039
0.1035 0. 1036
0. 1037 0.1036
0. 1036 0 . 1036
0.1038 0. 1036
0.1036
0. 1037

 

 

The value 0.1036 grams was used as the cadmium content of
the 24.94 milliliter ample.

The cadmium sample was added to a buffer solution
containing, for pH values below 7, varying volumes of
approximately ll amonium acetate and approximately ll
acetic acid such that their sum was equal to twenty
milliliters and the solution then diluted to roughly
ninety milliliters using distilled water. The cadmium
was then precipitated by adding ten milliliters of a
15 per cent solution of diamonium hydrogen phosphate
drOp by drop from a pipette with constant stirring to

-5-
the cold solution. For pH values above 7 approximately
1! amonium hydroxide and approximately 11! ansonium
chloride were used to buffer the solutions. In the case
of thehigh pH values, that is, above 9 the ammonium
hydroxide used was 6!.

All of the buffer solutions used for this work were
tested with standard cadmium ”mu... and found to give
no precipitate under the range of conditions used.

The samles were allowed to stand overnight after
precipitation and were then filtered through weighed
Gooch crucibles, washed free of chlorides with a one
per cent solution of the precipitating reagent and
finally three small portions of a sixty per cent alcohol
solution. The precipitates were then carefully ignited
using first Bunsen burners and gradually increasing the
flame until the final ignitions were made with leker
burners.

The results obtained, however, at the beginning of
this work when low pH values were us ed showed such large
errors that a standing period of about forty-eight hours
between precipitation and filtration was tried and the
samples were placed in an ice chest with a temperature
of about 10° 0. This treatment was followed for all ’
samples while the effect of pH was being studied. Later
after the optismm pH range was determined other standing
periods were studied.

-7-

The amount of cadmium_was calculated on the basis of
the ignition of the precipitate to cadmium pyrophosphate.

The pH values of the samples were determined using
the undiluted filtrates and a hydrogen electrode set-up
using a normal calomel half-cell without a salt bridge.
A.student's type potentiometer was used for the voltage
measurements. The set-up was checked periodically against
.05 M potassium.acid.phtha1ate solution which has a,pB of
3.97 and.was further checked several times during the course
of the work by using a glass electrode to verify the results
given with the hydrogen electrode set-up.

During the first part of this work several of the fil-
trates were made up to a volume of two hundred and fifty
milliliters in volumetric flasks, thoroughly mixed and.the
amount of cadmium determined on ten.milliliter portions
using the dithiazone color method of Leininger and Ann-
etrong (7). The results Obtained.were in good agreement
with the cadmium.error found in the pyrophesphate deter-
mination. Table 11 gives the results obtained.

TABLE 11
0d Peund in Filtrate Using Dithiazone

0d 0d.found. Error cd found in filtrate *
taken as 0d2P207 using dithiasone

 

 

 

 

 

0.1036 0.1659 7:-0.0007 0.0066
0.1036 0.1030 s0.0000 0.0006
0.1035 0.1029 -0.0007 0.0006
0.1036 0.1027 -0.0009 0.0007

 

 

 

 

 

 

-8-

The effect of the pH of the solution upon the pre-

oipitation of the cadmium amonium phosphate is shown in

Table III.

TABLE III

Effect of pH Upon Precipitation of Cadmium
Ammonium Phosphate

 

 

 

 

lo. 0d taken 0d found Error mgms. 0d pH
1 0.1066 0.0961 -6.6 6.4
2 0.1066 0.0977 -6.9 6.4
6 0.1066 0.1026 -1.1 6.0
4 0.1066 0.1016 -1.8 6.0
6 0.1036 0.1061 -0.6 6.6
6 0.1066 0.1029 -0.7 6.6
7 0.1066 0.1066 -0.6 6.6
6 0.1036 0.1066 ~O.3 6.6
9 0.1066 0.1033 -O.3 7.0
10 0.1066 0.1034 -0.2 7.0
11 0.1066 0.1066 -0.6 7.2
12 0.1066 0.1064 -o.2 7.2
13 0.1066 0.1064 -0.2 7.4
14 0.1066 0.1061 -0.6 7.4
16 0.1066 0.1066 -0.1 7.4
16 0.1036 0.1066 -0.6 7.4
17 0.1066 0.1066 0.0 7.6
16 0.1066 0.1066 -0.1 7.6
19 0.1066 0.1036 0.0 7.6

 

 

 

 

 

 

TABLE III
cont.

Effect of pH‘Upon Precipitation of Cadmium
Ammonium.Phosphate

 

 

 

 

no: «:6 taken" Cd found Error mm. Cd pH
20 0.1066 0.1066 -0.1 7.6
21 0.1066 0.1033 -0.6 7.6
22 0.1066 0.1061 -0.6 7.6
26 0.1066 0.1066 0.0 7.7
24 0.1066 0.1067 40.1 7.7
26 0.1066 0.1062 -0.4 7.9
26 0.1066 0.1064 -0.2 7.9
27 0.1036 0.1066 0.0 7.9
26 0.1066 0.1069 +0.6 6.0
29 0.1036 0.1066 40.2 6.0
60 0.1066 0.1067 +0.1 6.0
61 0.1066 0.1066 +0.2 6.0
62 0.1066 0.1066 40.2 8.0
66 0.1036 0.1062 -0.4 6.2
64 0.1066 0.1036 0.0 6.2
66 0.1066 0.1033. -0.6 8.3.
66 0.1066 0.1064 -0.2 6.6
67 0.1066 0.1029 -0.7 6.6
66 0.1036 0.1029 -0.7 6.6
69 0.1066. 0.1062 -0.4 6.6
40 0.1066 0.1062 -0.4 6.6
41 0.1066 0.1029 -0.7 6.6

 

 

 

 

 

 

TABLE III
cont.

Effect of pH Upon Precipitation of Cadmium
Amonium Phosphate

 

 

 

 

 

 

 

 

lo. Cd taken A cd found ' Error mgms. Cd

"‘72 0.1036 0.1026 6.6
46 0.1066 0.1062 -0.4 6.6
44 0.1036 0.1062 -0.4 6.6
46 0.1066 0.1061 ~0.6 6.9
46 0.1066 0.1026 -0.6 6.9
47 0.1066 0.1006 -6.0 9.4
46 0.1066 0.0996 -4.6 9.4
49 0.1066 0.0940 -9.6 9.6
60 0.1066 0.0941 -9.6 9.6

 

  
   

 

 

1 study of this table shows that the best pH range“
for the precipitation to take place lies between pH values
7.0 and 8.3. Below a pH of 7 the results are consistently
low and above a value of 8.3 the error increases rapidly.

In figure 1 the average error in milligrams of
cadmium has been plotted against pH values of the undiluted
filtrates. The results although not as consistent as it
was hoped do show that the proper range for the deter-
mination is between pH '7 and pH 8.3. The optimum pH as
obtained from the curve is at a pH of 7.7.

Very little difficulty was encountered due to the
residues of cadmium pyrophosphate turning dark colored
during the ignition period. Occasionally if the Bunsen

flames were raised too rapidly the residues became light

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

   

 

 

 

 

 

 

 

 

 

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7 7 . . . 7 777177. . . . 1. 7 . . . . . . . . . . . . . . . _ . . 7 . 7 . 7 . 7 7 771 7 . 7 . . . . . . 7 . .77

11.

7.77.... . ..7... . 71.. .,7. _ 17777.7...7..77

7. .... .. .. .771..._. .7 ...777 . . ..777 .. 7.7. ..7. .. 77.7. 7 .. ..7

Y. . . .F . . . . 7 . .. . 71171.7. . 7 .. 7 . 7 . 7 7 7 .7 . . . .. 7 . 7 . . . 7 7 7779 . ._ . . . 7 . . . . . - . . . 7 .* .. 7 7 . . . 7 7 7L

7... .. .. .. .7 7777 . . .....27fi77... . . 1177...“. 7 .7 77.1 7 . 7. . ....-.77717
P v . . . Q 4 4 O 4 e.7~ n _ . e . . s 4 4 7 1 u n 4 u u . 1 1 . . . 4 O .101e . . . 111 1.1 77 . e u . e n . C I 7 0 e174

v . . . .- 7 . . 7 . 7 . . e . . 77717 7 . . . . 7 . 7 . . . . 7 7 7 a . 7 . . . . 7 .77 . . . - . _ . . ..7w117va . . . 7 7 . . ..1 .7 7 . . O . 7 7 ., 7 7. 7 7

Y . .- . . . - 7 . 7 4 4 . . . 177. . . . m . . . 4. . . . 47. . 7 . . H . . . . 7 7 _ . 7 . . . 4 77.7111 . . . n . 7 . .7 . w . .7.:477 . .. v .i

7.7:.an ..HwH... ..77. a. 5. _.. .77.. . ...... 77.7 m; ”w .,b7.7.77..777.w . . .71 . .. . ..177777h77.7u:1,

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

-12-
grey in color but in no case did they turn black or dark
grey. lost residues remained pure white throughout the
ignition.

After the optimum pH range was determined the.
following five factors were studied separately:

(1) temperature between precipitation and filtration,

(2) standing time between precipitation and filtration,

(5) various amounts of precipitating reagent, (4) various
amounts of ammonium chloride, and (5) efficiency of alcohol
wash solution. The error in terms of milligrams of
cadmium was determined for each of these factors as
follows:

1. The results obtained for samples at 10° - 12° c.
and at room temperature are given in Table IV. The
samples used were all pipetted from the same pipette
used for standardizing the stock solution and the solu-
tions were buffered with one gram of ammonium chloride,
four milliliters of filtered dilute ammonium hydroxide
(one volume of 61! to five volumes of water) and the
precipitating reagent. 1 standing period of forty-
eight hours was allowed between precipitation and
filtration. The 10° - 12° c. temperatures were obtained

by using an ice chest.

-13-

 

 

 

 

 

 

TABLE IV
Effect of Temperature
10° - 12° 0. Room Temp.
lumber Error in pH of Error in pH of
mgm. Gd filtrate mgm. Cd. filtrate
m==—1_——1 -o.2 7.8 -o.1 7i
2 -O.2 7.8 -0.2 7.8
3 -0.1 7.8 -O.l 7.8 ‘
4 40.2 7.8 +0.1 7.8
5 00.2 7.8 40.1 7.8

 

 

 

 

 

 

It is apparent that the results are not improved
by the use of an ice cheat for the digestion period.
2. the effect of standing time between precipitation
and filtration of the cadmium ammonium phosphate is
shown in Table V. In each case the samples were
delivered from the standardization pipette and buffered
as described above. All determinations were carried
out at room temperatures. Ho definite trend is indi-

cated in any of the three standing periods studied.
TABLE V

Effect of Standing Between Precipitation and Filtration

 

 

16 hrs. 24 hrs. 48 hrs.

 

 

 

 

 

 

‘°' Error in pilot Error in H of Error in PE Of
mgn. Cd filtrate mgm. Gd f1 trate ‘ngn. Cd filtrate
1 :0.0 “—7.7 -o.1 5.7 -o.1 7.7
2 -0.2 7.7 -002 7.7 -O.2 7.7
3 -0.2 7.7 0.0 7.7 0.0 7.7
8 00.2 7.7 00.1 7.7 90.1 7.7

 

 

 

 

 

 

 

 

-14-

Standing periods of less than sixteen hours were
not tried since the most convenient working arrangement
was to make the precipitation in the late afternoon and
filter the precipitate the next morning. ‘Winkler (5)
however, reports that a standing period of two hours
might be sufficient if one is pressed for time and if
the corrections given by him are applied.

5. In Table VI the results of using various amounts
of the precipitating reagent are shown. All determinations
were made at room.temperature with a twenty-four hour
standing period allowed between precipitation and filtra-
tion. 1.15 per cent solution of diammonium hydrogen
phosphate was used as the precipitating reagent. The
samples were buffered as described before.

TABLE VI
Effect of Various Amounts of Precipitating Reagent

 

 

 

 

 

10 ml. 20 ml. 30 m1.
lo. Error in pH of Error in pH of Error in pH of
mgm. Gd filtrate mgm. Gd filtrate mgm. Cd filtrate
l 0.0 7.8 -0.1 8.0 0.0 8.1
2 0.0 7.8 0.0 8.0 40.1 8.1
3 -0.1 7.8 -O.2 8.0 90.1 8.1
4 -0.2 7.8 e0.l 8.0 +0.1 8.1

 

 

 

 

 

 

 

 

4. The data obtained from a study of the effect of
various amounts of ammonium chloride are presented in
Table VII. The samples were all buffered as before withu

the exception of the amount of ammonium.chloride which has

one, five and ten grams.

The precipitates were allowed

to stand twenty-four hours at room temperature before

filtration.

TABLE VII
Effect of Various mounts of Ammonium Chloride

 

 

 

 

 

 

 

 

 

 

 

lg. 101401 5g. 118401 10g. 13401
No. Error in] pH of Error in4 pH of Error in pH of
mgm. Cd filtrate mas. Gd filtrate mgm. Cd filtrate
—1 so.1 8.0 -o.1 7.5 -7.0 7.2
2 90.1 8.0 +0.2 7.5 -6.9 7.2
3 0.0 8.0 -0.2 7.5 -7.1 7.2
4 90.1 8.0 -0.2 7.5 -6.5 7.2

 

 

Ihen ten grams of ammonium chloride were used the
error was very large showing that for best results the
ammonium chloride concentration of the one hundred milli-
liters of solution-should be kept to not over five grams.

5. To determine if all of the diamonium hydrogen
phosphate from the one per cent wash solution was being
removed by the alcohol wash the following determination
was carried out. After the precipitate had been trans-
ferred from the beaker to the Gooch mat it was washed
with two one milliliter portions of alcohol. The Gooch
funnel was then thoroughly washed with distilled water
so as to remove any diammonium hydrogen phosphate wash
solution adhering to the funnel. Then five milliliters
of alcohol wash solution was used to wash the precipitate

and this alcohol was caught in a clean test tube.

. ~16-
transferred to a weighed twenty-five milliliter beaker
and evaporated to dryness on the steambath. The results
given in Table VIII indicate that the alcohol wash solu-
tion as used for this determination removes all of the
diamonium hydrogen phosphate adhering to the precipitate.

TABLE VIII
Residue From Alcohol lash Solution

 

Number I Igm. residue
1 0.0
2 0.0
3 0.0
4 0.0

 

 

 

 

The next step in this work was the working out of
a simple, easy method of adjusting the p11 of the sample
so as to have it within the permissible range. This
was accomplished by using the indicator phenol red
which changes color at pH 6.9 as determined with a
hydrogen electrode and adding amonium hydroxide until
the color change is noticed and then five drops in
excess. Table 11 contains the data obtained when the
following procedure was used. One gram of amonium
chloride was dissolved in sixty milliliters of distilled
water in a one hundred and fifty‘milliliter beaker.
Samples of the-standard cadmium solution were added
using the original standardization pipette. Two drops
of phenol red indicator were added producing a yellow

-17-
colored solution. Filtered ammonium.hydroxide ( one
volume of 6! to five volumes of water) was added from
a burette until the color changed from yellow to pink
and.then five drops in excess. The cadmium.was then '
precipitated.by adding ten.milliliters of a 15 per
cent diamonium hydrogen phosphate solution drop by
drOp from a pipette with.constant stirring. The
precipitate was allowed to stand sixteen hours at room
temperature and.then filtered.through a weighed Gooch
crucible. The precipitate was washed free of chlorides
using a one per cent solution of the precipitating
reagent and finally with.three small portions of a
60 per cent alcohol solution. The precipitate was then
'ignited as described in the first part of this work.
This method of adjusting the pH of the solution pro-

duced satisfactory results as the data in Table II

 

 

 

 

 

 

 

indicates.
TABEB IX
Test of pH Adjusting Procedure
Cd taken Gd found Error mgm. Cd, pH of filtrate
__0:1036 0.1036 0.0 7.7
0.1036 0.1037 00.1 7.7
0.1036 0.1037 00.1 7.7
0.1036 0.1036 0.0 7.7
0.1036 0.1034 -o.2 7.7
0.1036 0.1034 -0.2 7.7

 

 

-13-

The procedure was also checked using varying amounts
of cadmium sample and.produced satisfactory results for'
quantities of cadmium.greater than 0.04 gram. For
samples of less than 0.04 gram.the error is negative and
very large while for samples of more than 0.2 gram.the
error is positive but notexcessive as the data of

Table I shows.

 

 

 

 

 

 

 

TABEE.X
Results Using Varying Quantities of Cadmium
Cd.taken Cd found Error in Percentage
===: mgm. 0: erroi===J
0.0208 0.0198 -1.0 -4.80
0.0208 0.0202 -0.6 -2.88
0.0208 0.0198 -l.0 -4.80
0.0208 0.0200 -0.8 -3.84
0.0415 0.0418 90.3 90.72
0.0415 0.0412 -0.3 -0.72
0.1036 0.1036 0.0 0.00
0.1036 0.1037 90.1 90.09
0.1036 0.1037 90.1 90.09
0.1036 0.1036 0.0 0.00
0.1036 0.1034 -0.2 ~0.18
0.1036 0.1034 -0.2 -0.18
0.2075 0.2072 -0.3 -0.14
0.2075 0.2073 -0.2 -0.09
0.4151 0.4156 90.5 90.12

 

 

-19-

TABLE 1
cont e

Results Using Varying Quantities of Cadmium

 

 

Cd taken Cd found Error in Percentage
mgm. Cd error
0.4151 0.4162 91.1 90.26
0.5187 0.5195 90.8 90.15
0.5187 0.5202 91.5 90.28

 

 

 

 

 

Several samples were run in which the volume of
solution was varied and gave the results shown in
Table II.

TABLE XI
Effect of Varying Volumes of Solution

 

 

 

 

Error in mgm. Cd
Total Vol. Total Vol. Total Vol.

100 ml. 200 mm. 300 ml.

0.0 ~O.4 -0.8fi
90.1 -0.4 -0.7
90.1 -0.3 ~0.8

0.0

90.2

-0.2

 

 

 

 

 

From the results given in Table II it is evident
that the volume of the solution containing the cadmium
must be kept small for best results.

as series of unknown samples prepared by two other
workers in the laboratory were run using the phenol.

red method of adjusting the pH and gave the results

tabulated in Table XII.

TABLE XII

Unknown Samples

 

 

 

 

 

 

 

arms. Cd Grms. Cd Error in Percenta::=J
taken found mgm. Cd error
0.0400 0.0398 90.2 90.50
0.0600 0.0598 90.2 90.33
0.0999 0.0998 90.1 90.10
0.0999 0.0999 0.0 0.00
0.1399 0.1404 90.5 90.36
0.2001 0.2000 90.1 90.05
0.2598 0.2601 90.3 90.11
0.2997 0.3002 90.5 90.15
0.3000 0.2995 90.5 90.16
0.3397 0.3406 90.9 90.26
0.3996 0.4004 90.8 90.20
0.4003 0.3996 90.7 90.17

 

 

The samples for which a.positive error was obtained

were prepared by one worker in the laboratory and the
samples for which a negative error was obtained were
prepared.by another worker in the laboratory.

The errors were not excessive, however, for any
sample and.the method for determining cadmium.produced
acceptable results.

The directions for determining cadmium.by this

method are as follows:

-21-

The solution containing not more than 0.3 gram and
not less than 0.04 gram.cadmium.and no interfering sub-
stances should have a volume of approximately 75
milliliters. Add one gram.of ammonium chloride and two
drOps of phenol red indicator thus producing a yellow
colored solution. Add from a burette filtered ammonium
hydroxide (one volume of 6] to five volumes of water)
until the color of the solution changes from yellow to
pink, then add five drops in excess. Precipitate-the
cadmium by adding a 15 per cent solution of diamonium
hydrogen.phosphate drop by drop and.with.constant
stirring until five milliliters have been added. Allow
the precipitated cadmium ammonium phosphate to settle
slightly and test for complete precipitation. Ihen
the cadmium is completely precipitated add an excess of
ten.milliliters of the precipitating reagent drop by
drOp and with constant stirring. The volume of the
solution at this point should not be greater than 100
Idlliliters.

.Allow the precipitate to stand overnight and then
filter through a weighed Gooch crucible. Transfer the
precipitate to the Gooch crucible and wash with a 1 per
cent solution of diammonium hydrogen.phosphate until no
test for chloride is obtained. Remove any adhering wash
solution using three two milliliter portions of a 60

per cent ethyl alcohol solution.

-22..

Carefully dry the residues in the Coach crucible
using the smallest Bunsen flame possible. Gradually
increase the flame so that at the end of about four
hours a full Bunsen flame is being used. If the
residue begins to turn grey in color the flame must
be increased more slowly. Continue the ignition for
one hour with a full Bunsen flame and finally ignite
for one hour with a leker burner. Cool and weigh the
Coach crucible and ignite for one-half hour with a
leker burner, continuing this procedure until constant
weights are obtained. The cadmium pyrophosphate residue '
will be pure white in color.

-23-
sown

A method of determining cadmium.as cadmium.pyro9
phosphate by precipitating cadmium.ammoniumrphosphate
from.a solution of controlled.pH is described. Fairly
satisfactory results may be obtained for the precipita-
tion of cadmium amonium phosphate over a pH range of
7.0 to 8.3 for amounts of cadmium from 0.04 gram to
0.3 gram. The preper pH is indicated by the color change
of phenol red from yellow to pink. Below a pa of 6.5
and above a pH of 8.5 the results obtained are much
too low. A concentration of ammonium chloride between
one and five grams per 100 milliliters has no detrimental
effect.

1.
2.
3.

4.
5.

6.

'7.

-24-
BIBLIOGRAPHY

‘ultin' He, me Je 801e, g, 214, (1899)e
Dakin, s. 1)., 2. Anal. Chem., gg, 273-34, (1900).

“1191', Be He and Page, Re 'e, Chemo Centralblatt,
g_2_, 1181, (1901).

Winklor, Le 'e. Ze “89's Chane, ‘33-, ‘66, (1921)e

‘lillard, B. H. and Furman, N. 8., Elementary
Quantitative Analysis, 287, (1933).

Hillebrand, I. P. and Lundell, G. E. F., Applied
Inorganic Analysis, 206, (1929).

Leininger, E. and Armstrong, G.'I., Unpublished work.

 

 

   

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