chlorate is added to the warm solution after the expulsion of the hydrogen sulfide. A blank should be run using the same amounts of reagents and acid as for the sample. This procedure was used for the determination of antimony in samples containing pure antimony, antimony mixed with indium oxide, antimony mixed with indium antimonide, and pure indium antimonide. Spectrographically pure antimony was obtained from Johnson, Matthey and Co., Ltd.; indium oxide was prepared in the laboratory from high purity metal and examined spectrographically; indium antimonide (Midway Laboratory) was melted in vacuo, remelted in argon, and
then finely ground in a diamond mortar. The samples were prepared to give approximately 200-mg. quantities of antimony, and the latter was determined by the iodometric method, using a color end point and a potentiometric titration. RELIABILITY
Titrating potentiometrically, the accuracy of the method is within 0.2%. The spread in the results for the determination of antimony in indium antimonide is believed to be due to inhomogeneity of the sample.
OF METHOD
Indium does not interfere. The theoretical percentage of antimony for the formula InSb is 51.48; a value of 51.44 was obtained by potentiometric titration and 50.99 by color end point (Table I). This difference of nearly 1% may be the result of personal sensitivity to the color change, for it was difficult to determine the end point by visual observation.
LITERATURE CITED
(1) Scott, W. W., “Standard Methods of Chemical Analysis,” 5th ed., vol. I, p. 75, Van Nostrand, New York,
1925.
(2) Treadwell, F. P., Hall, W. T., “Ana-
lytical Chemistry,” 9th ed., vol. 11,
p. 94, Wiley, New York, 1951. (3) Zbid., p. 614.
RECEIVED for review May 23, 1956. Bccepted October 10, 1956.
A ppI ic a ti o n of t he Iro n(II)-T it a nium(III) T it ra ti o n Procedure to the Determination of the Nitrogen Content of PropelIants JOSEPH GRODZINSKI Central laboratory of Israeli Military Industries, Ministry of Defence, le1 Aviv, Israel
,A volumetric method for determining nitrate nitrogen in commercial nitrocellulose has been modified to make it applicable to the analysis of both military-type nitrocellulose and smokeless powders. The modification consists in using an acetic acid-acetic anhydride solvent mixture to prevent premature precipitation of the sample during the reduction step with ferrous chloride solution and in adding the hydrobromic acid separately. The proposed procedure has a precision of *0.02% nitrogen and an accuracy comparable to that of the Devarda and nitrometric methods.
S
methods for the determination of nitrate nitrogen have recentlg been discussed by Becker and Shaefer ( 2 ) . Only few of them proved to be applicable for the determination of the total nitrogen content of nitrocellulose propellants, which consists of a simultaneous determination of nitrocellulose and nitroglycerin nitrogen in the presence of other propellant ingredients. The most widely applied is the Devarda method, adapted to the determination of the nitrogen contents of smokeless powders by Muraour (10). Its application has since been extensively investigated, and several mndXcations have been suggested (6, 8, 9 , I I ) . However, it remains relatively timeEVERAL
150
ANALYTICAL CHEMISTRY
consuming and requires reagents of a very strictly defined specification, if the results are to be exact ( 3 ) . The application of the nitrometric method (12) to the determination of the nitrogen content of propellants is also possible, as has been suggested by Grodzinski and Berkowicz (6). The interference of stabilizers with the nitrometric determination may be eliminated by applying a correction based upon a linear relationship existing between the amount of stabilizer and the lowering of results. Four nitric oxide molecules are fixed by each ethyl centralite molecule and nine nitric oxide molecules by two diphenylamine molecules. This method requires, of course, an exact determination of stabilizers simultaneously with the nitrometric determination. The results of the iron(I1)-titanium(II1) volumetric procedure of Knecht and Hibbert ( 7 ) , applied by Becker (1) for the determination of nitroglycerin, are unaffected by stabilizers present in propellants. However, this procedure is not suitable for the determination of the nitrogen content of propellants because of the incomplete reduction of nitrocellulose. Shaefer and Becker proposed a modification of this method ( I S ) for the determination of nitrocellulose which consists of the inclusion of hydrobromic acid in the ferrous chloride reagent. They
claim that very exact results may be obtained by this procedure. Tranchant (14) was unable to reproduce the experiments of Shaefer and Becker with the same precision and the results obtained by him were still too low as compared with those obtained by the Devarda method. He proposes to add an ammonium molybdate solution to catalyze the reduction of nitrocellulose by the ferrous ion. The introduction of ammonium molybdate, as proposed by Tranchant, presents, however, a serious disadvantage by affecting the sharpness of the end point of the titration, which is completely imperceptible in colored ’ or opaque solutions-e.g., in the case of graphite-glazed propellants. The differences between the results obtained by Shaefer and Becker and by Tranchant may be due to the use of different types of nitrocellulose. In fact, in this laboratory the results of Shaefer and Becker were reproduced when samples of industrial nitrocellulose of high solubility were examined; with less soluble military grade nitrocellulose too low and irreproducible results were obtained. This may have been due to a partial reprecipitation of unreduced nitrocellulose from the acetic solution diluted viith water introduced with the ferrous chloride reagent. The author proposes to overcome this difficulty by applying as a solvent
an acetic anhydride-acetic acid mixture. The greater part of the water introduced with the ferrous chloride reagent is fixed by the acetic acid anhydride and the precipitation of nitrocellulose from the solution is prevented. A complete reduction by the ferrous ion is thus achieved in all types of nitrocellulose. Accordingly, a suitable procedure has been developed. The results have proved to be of the same accuracy as those obtained by the Devarda and the nitrometric methods.
ardized with a nitroglycerin or nitrocellulose standard sample. Hydrobromic Acid Solution. Mix 10 ml. of hydrobromic acid (specific gravity 1.377, about 40%) with 90 ml. of hydrochloric acid (specific gravity 1.19). Acetic anhydride, .glacial acetic acid, and hydrochloric acid (specific gravity I. 19), conforming to ACS specifications. Ammonium thiocyanate, 20%. PROCEDURE
Weigh in a high-form weighing bottle APPARATUS
The essential features of the apparatus and titration assembly are the same as those used by Shaefer and Becker ( I S ) . The main difference is the use of an Allihn condenser (Fisher Scientific Co., Catalog KO.7-734) instead of a Hopkins condenser. Into its outlet a rubber stopper with two openings is fitted. Through one of these openings a piece of glass tubing, connected with a glass washing bottle, is inserted. Through the second opening a 10-ml. pipet may be introduced. ilfter the pipet is removed, this opening is closed with a small rubber stopper or with a glass rod. A 10-ml. dropping pipet is used. It consists of a 10-ml. transfer pipet (Fisher Scientific Co., Catalog N o . 13-651) with a 20 to 30 mm. long rubber tubing connected to its upper end. The rubber tubing is closed with a screw compressor clamp (Fisher Scientific Co., Catalog KO. 5-871). The diameter of the bore of the rubber tubing is reduced by means of a capillary glass tubing inserted into
it.
High-form weighing bottles (Fisher Scientific Co., Catalog No. 3-410) are used.
a sample of 0.10 to 0.15 gram of pro-
pellant or nitrocellulose, previously ground to pass 40-mesh and dried for 24 hours in a vacuum desiccator over silica gel., Transfer the sample from the weighing bottle into the reduction flask. Add 30 ml. of glacial acetic acid and 30 ml. of acetic anhydride. Add particles of 10-mesh Carborundum and a glasscoated stirring bar. Close the necks of the reduction flask, and place it above the rotating magnet. Mix gently for some 30 minutes until the sample is completely dissolved. Attach the flask to the condenser, and connect with the rubber tubing leading to the carbon dioxide supply. Pass a current of carbon dioxide through the reduction flask. Add through the inner tube of the condenser 3 ml. of hydrochloric acid. Fit into the outlet of the condenser the rubber stopper connected as previously described. Introduce the
Table 1. Interference of Ferrous Bromide with Determination of the Nitrogen Content of Nitrocellulose Propellants Stabilized with Ethyl Centralite
REAGENTS
Ferrous Chloride Solution. Dissolve 400 grams of iron(I1) chloride tetrahydrate in 750 ml. of water, and a d d 100 ml. of 37% hydrochloric acid. Add about 5 grams of iron powder and heat on a steam bath for 10 to 15 minutes to ensure complete reduction of all iron(II1) ions. Filter the solution, saturate it with carbon dioxide, and preserve it under the inert gas atmosphere. The reduction procedure is repeated if during the storage some iron(II1) chloride has been formed, and 15ml. of 3775 hydiochloric acid are added. Titanous Chloride Solution, approximstely 0.2N. Prepare according t o the directions of English (4). Standardize it with nitroglycerin or nitrocellulose standard samples of known nitrogen content (determined with a nitrometer). If those :ire not available the solution may be standardized by means of 1Ies:tbi iron ore as described by Becker and Shaefer ( 2 ) . Ferric Ammonium Sulfate, approximately 0 . 2 5 for use as a secondary standard. Determine its concentration by titrating it with titanium(II1) chloride, which has just been stand-
K Found, yo Reduction Reduction Kith with 100 to 1 FeC12 solution FeCL-FeBr? (HBr added solution separately)
.4verage Std. dev.
Table II.
14 61 14 64 14 53 14.49 14 64
14 671 14 656 14 663 14 647 14.644
14.58 0.07
14.656 0.011
10-ml. dropping pipet filled with the ferrous chloride solution. Loosen slightly the screw clamps of the pipet so as to drop 20 to 30 drops of the ferrous chloride reagent per minute into the reduction flask. The temperature of the solution should rise gently. After all the ferrous chloride solution has been added, remove the pipet, add 2 ml. of the hydrobromic acid solution, close the opening, and allow the reduction to proceed by heating a t boiling temperature for 15 minutes. In the meantime weigh the empty weighing bottle. Add to the reduction flask 15 ml. of hydrochloric acid and 60 ml. of distilled water saturated with carbon dioxide. Continue heating for some 2 to 3 minutes until the color of the solution has changed to yellow-brown. Increase the current of carbon dioxide and cool the flask on a cold water bath. Disconnect the condenser. Set the flask on a magnetic stirrer, and titrate with the titanium chloride solution. Add 10 ml. of the ammonium thiocyanate solution as the end point is approached. Titrate to the point a t which the red color due to thiocyanate disappears. Carry out a blank determination. The blank value should not exceed 0.1 ml. of titanium(111) solution
where
S
=
B
=
E
=
milliliters of titanium(II1) required for titration milliliters of titanium(II1) required for blank determination normality of titanium(II1) chloride 0.4669 =
14.008 X 100 looo
RESULTS AND DISCUSSION
The blank value must be low if exact results are to be obtained. When a slight oxidation of the ferrous chloride solution takes place during its storage, it should be reduced with iron polvder (as previously described). However, such treatment is not satisfactory for a ferrous chloride solution containing hydrobromic acid; if this solution is used after its reduction, somewhat low
Nitrogen Content of Nitrocellulose and Nitrocellulose Propellants S Found, yo
Sample
Principal Devarda Nitromettic Titanium(I1I) Ingredients method method method 1 Nitrocellulose 12 46 12 47 12 47 ct 0 020 Kitrocellulose 13 22 13 23 13 22 zk 0 02= 2 3 Xtrocellulose, nitroglycerin, diethyl phthalate, ethyl centralite 14 92 14 93h 14 92 i 0 02c 4 Sitrocellulose, nitroglycerin, ethyl 12 S i 12 86b 12 85 i 0 O l d centralite, dibutyl phthalate Five determinations made. ilctual value found by nitrometric method corrected for nitration of stabilizer. Six determinations made. Four determinations made.
KO
a
b c
VOL. 29, NO. 1, JANUARY 1 9 5 7
151
and discordant results are obtained.
A similar effect has also been observed when ferrous bromide is added to the ferrous chloride solution (Table I). Therefore, the hydrobromic acid is put directly into the reduction flask. Some of the results obtained for the analyzed samples of nitrocellulose and nitrocellulose propellants are given in Table 11. They have been compared with the results obtained by the Desrarda and the nitrometric methods. The results are reproducible within = t O . O Z ~ oof the nitrogen content of the samples and are evidently in agreement with those obtained by the Devarda and the nitrometric methods. The proposed procedure is as convenient as the original ferrous-titanous titration procedure of Shaefer and Becker and seems to be generally applicable for the determination of the nitrogen content of
nitrocellulose and nitrocellulose propellants. ACKNOWLEDGMENT
The author wishes to acknowledge the assistance of Lena Herzog, who carried out much of the experimental work. This paper is published with the kind permission of the General Director of the Israeli Military Industries. LITERATURE CITED
(1) Becker,
(5) Fleury, G., Jourdin, P., Mdm. poudres 27, 179-81 (1937). (6) Grodzinski, J., Berkowicz, M., “Determination of the Nitrogen Content of Propellants by the Nitro-
metric Method,” unpublished report, April, 1952. (7) Knecht, E., Hibbert, E., “Xew Reduction Methods in Volumetric Analysis,” 2nd ed., p. 26, Longmans, Green, London, 1925. (8) Liogier, H., Mdm. pozidres 36, 309-13 11954).
Liogier,”., Dalbert, R., Tranchant, J., Ihid., 37, 466-8 (1955). Muraour, H., Ihid., 23,250-5 (1928). Parpaillon, N., Ibid., 34, 419-20 (1952).
w.IT7., IND.EKG.C m x ,
ANAL.ED.5, 152-4 (1933). W. W., Shaefer, W. E., “Organic Analysis,” Vol. 11, p. 97, Interscience, New York, 1954. (3) Brissaud, L., Tranchant, J., Xdm. poudres 36, 315-21 (1954). (4) English, F. L., J.Znd. Eng. Chem. 12, 994-7 11920). (2) Becker,
Pitman,’ J. R., J . SOC.Chem. Ind. (London) 29, 982-6 (1900). Shaefer, W.E., Becker, W.W., ANAL, CHEnf. 25, 1226-31 (1953). Tranchant, J., XXVIIth International Congress, Bruxelles, 1954. RECEIVED for review June 11, 1956. Accepted October 1, 1956.
FiItra tion-Precipitation Separation of Barium-140 from Lanthanum-I 40 R. W. PERKINS General Electric Co., Richland, Wash.
b A rapid method i s described for obtaining a continual supply of carrierfree barium- 140. Purified 12.8-day barium- 140 i s soon contaminated by growth of its 40-hour lanthanum-140 daughter. A method was developed for periodically removing lanthanum140 from the barium-1 4 0 by filtering the solution through an anion exchange bed in the free-base form. The lanthanum-140 i s precipitated on the resin and the barium-140 passes through in the effluent. The barium140 was shown to be radiochemically pure by decay and daughter growth rate measurements. The lanthanum140 can be removed from the anion exchange bed by acid elution. Its radiochemical purity was established by decay measurements.
140 mill reach about 1.5% 1 hour after purification. Numerous methods have been used for the separation of barium-140 and lanthanum-140, including formation of lanthanum-140 as a radiocolloid in basic solution followed by filtration 19), ion exchange (1, 2, 7), paper chromatography ( d ) , and precipitation (6) ; however, it was found that filtration of a barium-140-lanthanum-140 solution through a n anion [OH-] column for removal of the lanthanum-140 was a
more rapid and convenient means of obtaining carrier-free barium-140. This separation differs from the lanthanum140 radiocolloid filtration method (9) in that it involves the precipitation of lanthanum-140 on the surface of a resin rather than the filtration of a lanthanum-140 radiocolloid. A barium-140 solution can be repurified by this method as often as necessary to keep the lanthanum-140 below a n interfering level. The lanthanum-140 precipitated on the column may be re-
I
radioisotopic tracer studies, a constant supply of the radiochemically pure isotope is required. I n the case of 12.8-day barium-140 which has a 40-hour lanthanum-140 daughter, it is necessary to have a rapid method of purification, or the lanthanum-140 mill reach a significant concentration before any tracer studies can be made. The p activity of lanthanum-140 in purified bariumpr’ CARRYING OUT
152
ANALYTICAL CHEMISTRY
3 E F F L U E N T VOLUME,
Figure 1.
ML.
Elution of barium-1 40 with water
Column, 4 X 200 mm.; OH--charged Dowex 1 ( 8 % cross linked; 100 to 200 mesh, Lot 3562-18)
