VOLUME
2 7,
NO.
7,
JULY
1955
1199
reasonable, the coulometer must be standardized for practical use. Similar equations can be derived for the more complex situation when both the acid and base forms absorb. However, the agreement between theoretical and practical curves is not so good. In practice a solution of the indicator is prepared in a concentration of 0.1 to 1.0 X 10-4 mole per liter, depending on the color
intensity of the indicator. A standardization curve is plotted. Then one is prepared to use the coulometer. For the greatest sensitivity it is best to pass current until the readings are on the steep straight-line portion of the graph. The reproducibility of this portion of the curve is within the accuracy of the colorim-
eter. This coulometer is most useful in the range of 0.01 to 1.00 coulomb.
These colorimetric coulometers with the wide variety of reactions available offer possibilities for use in numerous cases where small quantities of electricity are to be measured. LITERATURE
CITED
(1) Lingane, J. J., “Electroanalytical Chemistry,” 246-50, Interscience, New York, 1953. (2) Lingane, J. J., J. Am. Chem. Soc., 67, 1916-22 (1945). (.3)
Wartenberg, H. v., and Schütza, ., Z. Blektrochem., 36, 256-7 (1930).
Received for review November 3, 1954.
Accepted February 23, 1955.
Determination of Small Amounts of Chlorate in Ammonium Perchlorate CHAIM
EGER
Scientific Department, Israeli Ministry of Defence, Tel-Aviv, Israel A colorimetric microdetermination of chlorate in ammonium perchlorate is based on the production of a colored substance from brucine with chloric acid.
ammonium perchlorate is to be used in explosive or compositions, it must be practically free of chlorate, for chlorate lowers the temperature of deflagration of ammonium perchlorate considerably. According to the standard texts, the chlorate concentration should not exceed 0.02% (4). The methods for the determination of chlorate (7), which are based on the reduction of the chlorate to chloride, are cumberThe method recommended by Lunge (3)—i.e., reduction some. of the chlorate with ferrous sulfate and titration of the ferrous ion in excess with potassium permanganate—did not give consistent results. The colorimetric methods suggested (3) did not seem to be reliable. Therefore, an adaptation of the color reaction with brucine ((J, 7) was worked out for use in quantitative analysis.
WHEN pyrotechnic
EXPERIMENTAL
Reagents. Brucine, Revector indicator preparation (Hopkins and Williams). The 5% (weight by volume) solution of the reagent in glacial acetic acid (AnalaR) was kept in a glassstoppered bottle. Sulfuric acid, 30 to 32%, is prepared by dilution of 80 ml. of sulfuric acid (AnalaR, density 1.84) with distilled water to 250 ml. The purity of the sulfuric acid is of prime importance. Acid with a dark tint gives consistently low results. Potassium chlorate (May and Baker) was recrystallized once from water and dried.
Ammonium perchlorate was prepared by neutralization of technical perchloric acid with ammonium hydroxide solution and recrystallized four times from water. It was completely free from chlorate, as indicated by the negative spot test with brucine
(2). The standard solution of ammonium perchlorate contained an amount of potassium chlorate equivalent to 0.02% of ammonium chlorate. A quantity of 120.8 mg. of potassium chlorate was dissolved in 100 ml. of distilled water. Five grams of ammonium perchlorate (solubility 10.74 grams per ml. of water at 0° C.) were weighed into a 50-ml. volumetric flask and were dissolved in the required amount of distilled water.. Then this solution, to which 1 ml. of the potassium chlorate solution was added, was made up to volume with water. This solution is equivalent to 0.02 weight % of ammonium chlorate in ammonium perchlorate. Apparatus. A Hilger Spekker absorptiometer H760 was used, fitted with No. 1 Kodak filters (transmittance at 405 to 455 µ) and 2-cm. Corex absorption cells. The filter was chosen in accord with the absorption spectrum of the color produced in the reaction (see Figure 1). The principal spectral band lies at 435 mu. The absorption spectra were measured with a Beckman DU quartz spectrophotometer, using 1-cm. quartz cells. Procedure. Preparation of Calibration Curve. From an automatic 5-ml. microburet, fitted with a long capillary tip which reached to the center of the volumetric flasks, 0.5, 1, 2, 3, 4, and 5 ml, respectively, of the standard solution were measured into six 25-ml. volumetric flasks and 5 ml. of distilled water into a seventh one (this gave the same blank as ammonium perchlorate solution). Then 10 ml. of ice-cold sulfuric acid was added to each flask, and the neck of the flask was rinsed with the acid to remove traces of adhering substance; then the flasks were shaken thoroughly. Finally, 0.5 ml. of the brucine solution was added and the content of the flasks was mixed again. The flasks were immersed in a boiling water bath for 15 minutes, cooled with ice, and filled up to the mark with distilled water. The color of the solutions was then measured against that of the blank, and the absorbance (D log I0/I) plotted against weight per cent of ammonium chlorate in ammonium perchlorate. A straight line was obtained from the observed points of 0.01, 0.C2, 0.04, 0.06, and 0.08% of ammonium chlorate, respectively, absorbance 0.0448,0.0880,0.1798,0.2750, and 0.3624. For best results, measurements should be made immediately after the formation of the colored product is completed. The intensity of the color remains constant at a temperature of 10° C. for 2.5 hours. After 20 hours, a 6.5% decrease of the absorbance has been noted. Analysis of Unknown Samples. A quantity of 10.00 grams of the ammonium perchlorate sample was weighed into a 100-ml. volumetric flask, dissolved in distilled water, and made up to volume. If the sample contains insoluble impurities, the solution must be filtered. This solution, 1 to 5 ml. (depending on the chlorate content), is measured into a 25-ml. volumetric flask and the analysis is carried out as described. Using the calibration curve, the chlorate content is determined from the absorbance measured. =
WAVE LENGTH, Mm
Figure
1.
Five per
cent
Absorption spectrum colored compound
glacial acetic
brucine
of
solution, 0.5 mg., in acid, containing 0.008% of potassium chlorate
RESULTS
Some of the results obtained are summarized in the following
tables.
ANALYTICAL
1200
Table I. as
CHEMISTRY
Absorbance Differences (against Blank Value) Function of Ammonium Chlorate Content"
% Ammonium
Chlorate
Perchlorate 0.01 0.02 0.04 0.06
a
Absorbance X
103
1
2
3
4
5
045 088 180 275 359 430
047 088
045 089
045 087 179 269 368
042 088 180 273 361 445
0.08 0.10 Five determinations.
Table II.
181
179
275 363 434
278 361
435
WAVE LENGTH, µ
Error in Chlorate Determination % Ammonium Chlorate
Detn.
Added"
9 15
0.01
Found 0.0096 ± 0.00025 0.02 0.0194 ± 0.00019 15 0.04 0.0398 ± 0.00025 10 0.06 0.0606 ± 0.00028 ± 0.00033 10 0.08 0.08 9 0.10 0.096 ± 0.00148 Calculated from potassium chlorate added.
Difference -0.0004 0.0006 -0.0002 0.0006 -
0
-0.004
The method gives excellent results below the 0.1% concentration of ammonium chlorate. For concentrations greater than 0.1%, the results tend to become somewhat low. Regarding the possible interference of foreign ions, systematic experiments were carried out with chloride and ferric ions. As much as 0.1% of ammonium chloride in the ammonium perchlorate had no effect. The ferric ion did not interfere up to a quantity of 0.005%; larger amounts gave too high absorbance readings. Samples containing large quantities of iron ion should be treated with ammonia solution and then filtered to remove the iron ion. Periodate and nitrate interfere with this method. However, iodate gave no measurable color with the reagent below the 0.033 weight % concentration in the ammonium perchlorate. These ions are not likely to be present in samples of ammonium perchlorate. Heating of the solution from 15 to 30 minutes had no adverse effect on the accuracy of the analysis.
Figure 2. Absorption spectrum of brucine 5.1 mg., in 1 ml. in glacial acetic acid, diluted successively with 30% sulfuric acid
Brucine,
ring system of the former is oxidized by the chloric acid. It is most likely (supported by unpublished results on the determination of nitroglycerin with brucine), that all oxidizing agents convert brucine into the same compound or at least compounds characterized by the same chromophoric groups. ACKNOWLEDGMENT
The author wishes to express his appreciation to Ernst IX Bergmann for his advice and to Shlomo Weinstock for providing the ammonium perchlorate used in this investigation. LITERATURE
CITED
(1) Berl, E., and Lunge, G., “Chemisch-technische Untersuchungsmethoden,” 8th ed., Vol. Ill, pp. 1170-1, Julius Springer,
DISCUSSION
Berlin, 1932. (2) Feigl, F., “Spot Tests,” Vol. I, p. 301, Elsevier, New York, 1954. (3) Kast, H., and Metz, L., “Chemische Untersuchung der Sprengund Zuendstoffe,” p. 379, Friedr. Vieweg und Sohn, Braunschweig, 1944. (4) Ibid., p. 384. (5) Snell, F., and Snell, C. T., “Colorimetric Methods of Analysis,” 3rd ed., Vol. II, p. 717, Van Nostrand, New York, 1949. (6) Welcher, F. J., “Organic Analytical Reagents,” Vol. IV, p. 215, Van Nostrand, New York, 1948. (7) Wischoe, F., J. Chem. Soc., 112, II, 539 (1917).
Comparison of the absorption spectra of brucine (Figure 2) and the colored compound (Figure 1) leads to the hypothesis that the
Received for review May 7, 1954. Accepted December 29, 1954. These experiments were carried out under the auspices of the Scientific Department, Israeli Ministry of Defense.
Spectrophotometric Determination of Nickel in Tungsten Powder KENNETH L. ROHRER1 Tungsten and Chemical Division, Sylvania Electric Products, Inc., Towanda, Pa.
method has been developed for the determination of microgram quantities of nickel in tungsten powder. With this method the nickel is separated from all interfering elements by a chloroform extraction of the bivalent nickel complex of dimethylglyoxime in the presence of the hydrogen peroxide used is to dissolve the metal powder. The determination of the made by spectrophotometric measurement diethyldithiocarbamate complex of nickel. Nickel, 1 to 50 y, can be determined in tungsten powder with an average deviation of less than 1 y. A rapid and accurate
if present within the crystal structure of tungsten As as a dope will alter its physical properties. an impurity, its accurate determination is usually lengthy and it requires a preliminary separation before a suitable colorimetric method can be utilized for the small amounts present.
NICKEL powder or
Fettweis (3) has attempted to determine nickel in tungsten steels by precipitating with dimethylglyoxime, but found that the
nickel precipitate of dimethylglyoxime retains some tungstic oxide and that results are from 0.05 to 0.1% high. However, no previous methods for the determination of small amounts of nickel in tungsten powder have been reported. Dimethylglyoxime has been mentioned frequently in the literature as a reagent forming a soluble, colored complex with nickel, either complexing with quadrivalent nickel, or if oxidized complexing with bivalent nickel. This reagent has long been used for the detection of nickel (3). Bivalent nickel can be separated by a chloroform extraction of the insoluble, bivalent nickel complex of dimethylglyoxime (6). Oxidizing agents such as nitrates, ferricyanides, peroxides, and permanganates have been reported to prevent the formation of this insoluble nickel prePresent address, Westinghouse Electric Corp., Elmira, N. Y.
