INDUSTRIAL A S D EKGISEElU\ G CHERIISTK’k
628
shift a t internal reflection, since the intensity of the portion of the field in question is notfound to be reduced appreciablS, when a quarter-wave plate is inserted in various azimuths and the analyzer is rotated. It is observed, as would be expected, that the reversal of the fields is more distinct when the film is birefringent t,han it is optically isotropic; but qualitatively there is litt’le difference between films of Ti-eak and of stronger birefringence. The polarizing method is of considerable practical advantage in a laboratory where refractive index measurements are made on a large number of thin films and the time element is important. A Polaroid microscope cap analyzer, such as the one listed by the Bausch &I Lomb Optical Company and which fits over eyepieces up to 27 mm. in diameter, has been found to be suitable for
S’OL. 1 0 , NO. 11
t h e purpose described.
Such an analyzer is, of course, a necessity in identifying the double boundaries observed when birefringent films or crystals are examined on an Abbe or other total reflection refractometer(4). Bellingham and Stanley (London) are noT5- offering an Abbe refractometer Kith polarizing eyepiece ( 2 ) . The polarizing screen for the illuminator may be obtained from t h e Polaroid Corporation or other dealers. The combination of polarizing screen and cap analyzer may be used in a simple polari.cope f o r examination of specimens preliminary to their nieaiurement .
Literature Cited (1) Bradley, T. F., ISD.EXG.CHEW,Anal. Ed., 3, 304 (1931). (2) Guild, J.,J . Sci. Instrunzents, 15, 65 (1938). (3) Morrell, R. S.,ed., “Synthetic Resins and Allied Plastics,” p. 356, New York, Oxford University Press, 1937. (4) ITest, C, D., J . CILemn. sot,, S9, 7 4 2 (1937), RECEIVED June 17, 1938.
Effect of Ions on Mohr Method for Chloride Determination Hydrogen Peroxide Modification for Sulfite Elimination R. T. SHEEN
AND
H. L. KAHLER, W. H. &- L. D. B e t z , Philadelphia, Pa.
The Mohr method is found to be unaffected by ions, except sulfite, that are prevalent in steam condensate, raw and mixed boiler feed waters, and in boiler salines. A modified Mohr method is suggested for the elimination of sulfite and is proved to be satisfactory. pH between 7.4 and 10.8 has no effect on the method.
The work showed that sulfite interfered, giving high results. The effect of this ion is also presented in the diagram. I n the low range of chloride, ion concentrations of 328 p. p. m. of sulfate, 400 p. p. m. of total alkalinity as calcium carbonate, 600 p. p. m. of total hardness as calcium carbonate, 20 p. p. m. of phosphate, 40 p. p. m. of silicate expressed as SiOz, and 260 platinum units of color were found to have no influence. Sulfite also interfered in this range. I
I
I
I
1
T
HE Rlohr method (1) and modifications of it for the
determination of chlorides are widely used in boiler feedwater studies and yet a fairly exhaustive search of the literature has failed to disclose complete studies of the effects of the ions prevalent in these waters. Although it was felt that the majority of the ions exert no influence, the present investigation was planned to ascertain just what ions affected the method and to what extent. Because of the nature of the maters involved in this work, the study of these effects lent itself to subdivision into low and high ranges of chlorides, the former ranging from 0 to 10 p. p. m. and being representative of what would be encountered in steam condensate and in raw and mixed boiler feed waters, and the latter ranging from 10 to 1000 p. p. m . of chloride and representing concentrations encountered in boiler salines. Owing to the absence of adequate samples of rarious chloride concentrations, synthetic solutions were prepared with known chloride concentration, and the particular ion or ions (chloride-free) to be studied were introduced prior to the titration. Table I presents the results of this work. Reference to Table I will reveal that the method under these conditions was unaffected in the high chloride range by 3000 p. p. m. of sulfate, 100 p. p. m. of total hardness as calcium carbonate, 400 p. p. m. of silicate expressed as Si02, 160 p. p. m. of phosphate, 40 p. p. m. of iron (ferric), 2000 p. p. m. of total alkalinity as calcium carbonate, and approximately 10,000 platinum units of color obtained from tannin.
I
200 -
$ 0“ ’
100 -
O
/
OPOIN4RY BURG7
MiC408UDFl
/O’
L.11
0
10
I
I
30
40
I 20
SO
C/, PPM.
The diagram s h o w that considerable sulfite is required to give an appreciable interference. This being the case, solutions containing low sulfite and high chlorides will not be seriously affected by the presence of this ion. When, however, the sulfite content is high and the chloride concentration low, the error in the chloride determination can be serious. T o eliminate the effects of sulfite, the following procedure was found to be satisfactory: After neutralization of the sample to pH 4.3 (methyl orange end point), 2 cc. of hydrogen peroxide (3 per cent by volume) are introduced. The solution is stirred and reneutralized to the alkaline side of methyl orange. This reneutralization step is necessary because the sulfuric acid present in the hydrogen peroxide reduced the pH value, giving slightly high results due to the fugitive nature of the end point. The solution is then ready for titration with silver nitrate after the addition of the chromate indicator. The results using this procedure are presented in Table 11.
hKALITICAL EDITIOS
NOVEllBER 1 5 , 1938
TABLE I. EFFECTSO F 7
Expt.
Introduced
P. p.
m.
400 1000
Total SO4 Total H alkalinity P.p.m. P.p.m. P.p.m. Hieh Ranee of Chloridec
Variation P. p . m. 0 -2 0 -2 0 +I2 0 +2
400 98 400 412 400 402 440 424 414
100 400 400 400 400 400 400 400
I O N S I N C H L O R I D E DETERUIS.\TION
Ions Present
400 QQU ...
400 ~. .
11
Chloride Found by titration P. p . m.
629
...
...
3280
120
... ...
... ...
,..
++f 424140
,..
P.p.m.
... ... ...
... ... ...
... ,.. ... ... ...
... .). ... ... ... ... ... ...
... ...
...
...
160
...
48
2000
160
, . .
... ..
...
, . .
... ...
200 100 50
, . .
...
Poi
S03a P.p.m.
...
Si02 Fe P.p.m.P.p,m.
...
... ... ...
...
400
... ...
,..
... ...
,..
...
40
... ...
40
. . ...
...
...
Colorb P . P . ~
....
....
10,000
.... .... ....
.... ....
....
....
. . .
Low Range of Chlorided ... ... ... ... . . +0 6 10 "0 -0.4 '3'2'8 .,. 400 ... , . . . ... 10 f5.2 328 600 . . ... 40 40 500 n 10 328 600 40 230 0 +6.6 ... ... 40 0 +0.2 ... 20 0 10 ... +3 1 f0.4 ... , . . .... 5 -0.8 ... , . . ... ... ... . . .... ... 10 ... ... ... 10 ... ,.. .... f 3 a Solid sodium sulfite introduced into titration system immediately hefore titration. 1000 t o 10,000 p. p. rn. of mannitol ujed t o preserve So3 during analysis. b Expressed in platinum units of color. e Condition- for high range: Silver nitrate 1 cc. = 1 mg. C1-. Ordinary buret. 25-cc. sample neutralized t o methyl orange end point. 0.2 cc. of 10% neutral potassium chromate. 0.1-cc. blank. 50-cc. sample. 0.22-cc. blank. d Conditions for l o w range: Same as for high range except for microburet.
10
10 6 9.6 l5,2 10 0.6 0 2 3 1.4 4.2 13
COMP.\RATIT.E RESULTSOF PRECIPITATICN, h l O H R , ASD ?rlODIFIED hIOHR XfETHODS
TABLE11.
TABLE IJ-, EFFECT OF ~ € ON 1 NOHRMETHOD Chloride Found P . p . m.
7
Present Precipitation Regular LIohr method" method P.p . W L . P . p . m. 1 97.9 122 2 252 278
Eupt.
3 4 5
123
140 8.7 15.5
7.4
13.2
so3
HgO? modified method P . p . ni. 100 254
Present5
Type of Sample
Expt.
Boiler Boiler Boiler Raw Raw
a
1000 t o
8 9 10 11
96 l50c 50 5
124 6.6 12.6
7
Precipitation as AgC1. Sodium sulfite introduced directly before analysis of samples. 10,000 p. p. m. of mannitol used t o preserve 903 during analysis. c Approximate. a b
TABLE 111.
a
C O M P O S I T I O S O F SOLUTIONS r s E D IN
1
Present
2 Absent
3 Absent
4 Absent
4
Ga
7'3
12 13
Table I1 shows that the hydrogen peroxide procedure for sulfite elimination gives good results when compared to the precipitation method as silver chloride. The regular X o h r method gave high results because the sulfite x a s not eliminated. The results under the modified method were of acceptable accuracy. Each of these experiments except S o . 2 fits very well the curve presented in the figure. The sodium sulfite introduced in experiment 2 was only approximate. Table I11 presents the composition of the solution used in Table 11.
Experiment Suspended matter
1 2 3
P.p . m
TABLE 11 J
Absent
Expressed as calcium carbonate.
During the course of this study, the effect of p H on this determination was investigated. Inasmuch as the chromate indicator buffers the solution all pH measurements were carried out (electrometrically) after the addition of the indicator. The results are presented in Table IT', which shows that the same results were obtained when the titration was performed in any part of the p H range of 7.4 to 10.8. Experiments on solutions above pH 10.8 and below p H 7.4 gave unsatisfactory results, especially in the low range of chloride.
0
P.p .
vi.
Variation P. 1.'. m.
400 400 400 400 400 400 400
308 402 400 400 402
+;- 2
5.3 5.3 5,3 5.3 5.3 5.3 5.3
16 G
+11.3
.. ..
5.4 5.2 5,l
14 15 5.3 16 5 3 1ia 5.3 S o end point obtained.
5.0 5 6 6.2
8.4 3.2
..
pH of Solution 11.1 10.5 9.9 7.7 6.4 5.4 2 9
0
+2 .. ..
f0. 1 -0.1 -0.2 -0.3 +0.3 +0.9
+3.1 -7 - 1
..
11.3 10.8 10.6 8.8
7., 7.4 7.0 7.0 7.0 5 6
The color reactions of these titrations throughout this pH range of 7.4 to 10.8 were the same, slightly better end points being obtained in the higher pH region. Laboratories which determine chlorides after the analysis of alkalinity titrated to the methyl orange end point incur no error by this procedure, because the chromate buffers this solution from pH 4.3 to 7.7, which is within the acceptable range.
Conclusion The l l o h r method for chloride determination is affected by the presence of sulfite and unaffected by sulfate, total alkalinity, total hardness, phosphate, silicate, iron, and color in quantities that are prevalent in these types of water. The hydrogen peroxide modification of this method suggested for sulfite elimination was found very satisfactory. p H between 7.4 and 10.8 Tvas not found to affect the method.
-4cknowledgment The authors wikh to acknowledge the financial assistance and spon-orship of TI7 H. 6- L. D. Betz, in ~vlioselaboratories this v-ork n-as completed.
Literature Cited (1) " b t a n d a r d M e t h o d s ior the E x a m i n a t i o n oi W a t e r and S e w a g e , " 8th e d . , X e w York, A m e r i c a n P u b l i c H e a l t h A s s o c i a t i o n . 1cl?G RECEIIE D July 29 1938
