ANALYTICAL CHEMISTRY
382 hydroxide solution This quantity is well within the amounts used in elementary qualitative analysis. In addition, it is found that 1 mg. of cobalt gives an excellent test in the presence of 15 mg. of nickel; 5 mg. of cobalt and 50 mg. of nickel cause the formation of a blue-tinged lightgreen precipitate xhen analyzed by the above procedure. In the cases of high concentrations of nickel as compared to cobalt, the test is best made by comparing the color of the precipitate with the color of nickel hydroxide free of cobalt, formed with the same reagents.
LITERATURE CITED
(1) Alvarez. E. P., Chern. News, 94, 306 (1906) (2) Donath, E., Z.anal. Chern., 40, 137-41 (1901). (3) Hogness, T. R., and W. C. Johnson, “Qualitative Analysis and Chemical Equilibrium,” 3rd ed., New Sork. Henry Holt and Co., 1947. (4) Reiohel, F., Z . anal. Claern., 19, 468-9 (1880) ( 5 ) Scholder, R., and Weber, H., %. anorg Chem., 216, 159-64 (1934). (6) Wenger, P., Duckert, K.,and Busset, 11.L., Hdv. Chim. Acta, 24, 657-70 (1941). RECEIVED July 19, 1950
Dark-Chamber Titrimeter for Chemiluminescent Indicator Titrations in Colored Solutions FREDERIC KENrVY AND R. B. KURTZ Hunter College, iVew Y o r k , .\. 1..
T H E instrument described obviates the use of a dark room in A titrations employing a chemiluminescent indicator. It can be used in a brightly lighted room. Ferrous solutions, highly colored with sufficient chromic ion to prevent the use of the usual redox indicators, were titrated with ceric sulfate, using siloxene indicator. I n the absence of chromic ion, the results were high by 1.3 parts per 1000. In the presence of 0.16 Mchromic ion, the error increased to 3.3 parts per 1OOO. When the indicator correction was applied this error was diminished t o 2.0 parts per 1000.
900
seo
840-
-6 a20 -
>’ soo5
DESIGN OF TITRIMETER
The instrument used, shown in section in Figure 1,is a lighttight box, A , with black interior walls, provided with a stirrer, C, a buret, B, and an opening, F , for observing the end point. The opening is so constructed that no light can pass into the box when the observer’s eyes are a t the opening. The stirrer may be eithermotordriven or hand-operated.
Table I.
z
0 760 -
a W E 740 --
IE
F
Titration
M1.
Deviation from Mean. hl1
7201
W
-A
‘ 0 f-
z w
mor
6601
Figure 1 . Dark-Chamber Ti trimeter
Volume of Ceric Solution Equivalent, to 30.00 M1. of Ferrous Solution at 23” A 2” C. Ceric Solution,
-
780
c3
SILOXENE INDICATOR
The structure, preparation, and behavior of the siloxene indicator employed have been described ( 4 ) . The chemistry
-
a60
Potential Difference (from Curves),
Mv.
Deviation from Mean,
640 --
I
600,
580
I
r
p
P
d /
MV.
2 2
VOLUME Mean
29.87
0.015
751
3
OF CERIC SOLUTION ML.
Figure 2. Titration Curves Used in Locating Soitchiometric Point
V O L U M E 2 3 , NO. 2, F E B R U A R Y 1 9 5 1
940
383 with ceric sulfate solution, each drop of ceric sulfate added produced a momentary bright spot. When the stoichiometric point was reached, the sudden increase of oxidation potential brought about reactions within the suspended indicator particles which caused light t o come from all parts of the solution and to persist for a considerable time. This was taken as the end point.
9 P -
S O900
-
880
-
860
-
f
EXl’ERI3IENTAL
-
840
t22
5
ilpproxiniately 0.1 -11 solutions of ferrous ammonium sulfate and ceric sulfate were prepared. These solutions mere compared by titrating eight 30.0O-ni1. portions of the ferrous solution with the ceric solution, using a gold indicator electrode, a saturated calomel reference electrode, and a, Leeds and Xorthrup 7660-A vacuum tube potentiometer a t 23 + 2 ” C. Because the curve for the reaction is symmetrical with respect to the stoichiometric point, the midpoint of the nearly vertical portion was taken as t,he end point.
32;
25%
MEAN END POINT
ol-2
(SILOXENE INDICATOR)
820 -
-
800
The eight curves are shown in Figure 2 and the mean curve in Figure 3. As shown in Table I, the curves of Figure 2 yield a n average value of 29.87 ml. for the volume of ceric sulfate required to reach t,he end point, with an average deviation of *0.015 ml., which corresponds t o a precision of 0.50 part per 1000.
-i
>: 7802
-
760
I n order to test the dark-chamber Titrinieter and compare its performance with that of the dark room (4), five 30.00-ml. portions of the ferrous solution were titrated in the dark chamber with the ceric solution, using 100 mg. of siloxene indicator. The results are shown in Table 11. In order to test the effectiveness of the indicator in the presence of a highly colored component, five 30.00-ml. portions of the ferrous solution were titrated in the dark chamber with ceric solution, using siloxene indicator. Solutions titrated were 0.16 M with respect to chromic ion and had sufficient depth of color to make the use of any of the ordinary redox indicators utterly impossible. The results are set forth in Table 11.
+STOICHIOMETRIC POINl POTENTIOMETRICALLY DETERMINED
c3
z 740 P
a 720
-
700
-
C,,
02
w Iw
2
680-
-
660
z
W I- 6 4 0 -
0
a . 620-
600
-
580
-
560
L
I
I
I
I
j”,
d
I
I
0
0
0
0
0
0
N
N
N
N
N
n
~ ) w b m m dvioiuioid
t
I
o
VOLUME OF CERIC SOLUTION ML. . Figure 3. Average Curve Showing Range of End Points with and without Chromic Ion of siloxene and its drrivatives has heen discussed by Kautbky (S), and brief sunimaries in English are to br found in some treatises 011 inorganic chemistry (1. 2 ) . In the titration of ferroup solution
When chromic ion is absent, the average deviation of a single observation of 0.02 nil. corresponds t o a precision of 0.67 part per 1000. The indicator error-namely, 29.91 minus 29.87 or 0.04 ml. -is the same as the value previously reported ( 4 )when a dark room instead of a dark-chamber Titrimeter was used. In the present n-ork this error corresponds to an accuracy of 1.3 part,s per 1000. When chromic ion is present,, the average deviation of a single observation of 0.05 ml. corrt,sponds to a precision of 1.6 parts per 1000. The indicator rrror-namely, 29.97 minus 29.87 or 0.10 nil.-corresponds to an error of 3.3 parts per 1000. The accuracy of this tit,ration could be improved by using siloxene in standardizing the ceric solution or by applying the indicator correction. If the indicator correction w r e a p p l i d , t,he accuracy would become 2.0 parts per 1000. The difference of pot,ential at, the end point when t,he ceric sulfate was standardized and a t the end point R-hen siloxene indicator was used in the absence of chromic ion-namely, 848 minus 751 or 97 mv.-agrees fairly WPII with t,he value of 87 mv. previously reported (4). When t,he solution titrated was 0.16 M with respect t,o chromic ion, the difft,rc~ict% was 861 minus 751 or 110 mv. LITERATURE CITED
(1) Enieleus, H. J., and Ander-
Table 11. Volunie of Ceric Solution Equivalent to 30.00 M1. of Ferrous Solution and Corresponding Potentiometer Readings Using Siloxene Indicator at 23” * 2” C. I n Absence of Chromic Ion
-
A
r
Ceric bolution, mi.
Dei. from mean, nil.
Porenriometer reading, mv.
3fean 2 9 . 9 1
0.02
848
- ---
In Presence of 0.16 M Chromic Ion A
Dev. f t o m mean, m V.
Ceric solution, ml.
Dev. from mean, ml.
18
29 9;
0.05
-
Potentiometer reading, mv.
Der from mean, mv.
86 1
41
son, J. S., “Modern Aspects of Inorganic Chemistry,” p. 315, New York, D. Van Nostrand Co., 1939. ‘2) Ephraim, F., ”Inorganic Chemistry,” 4th English ed., p. 834, New York, Interscience Publishers, 1947. (3) Kautsky, H., KoZZoid Z.,102, l(1943). i4) Kenny, F., andKurtz, R. B., AXIL. CHEM., 22, 693 (1950). RECEIVED J u q 6, 1950.
