880
V O L U M E 19, NO. 1 1
phthalic anhydrides, it was found that any appreciable excess of the anhydride over the amount required to react with the water in the reagent always led t o excessive darkening during the decarboxylation and to the evolution of more than the theoretical quantity of carbon dioxide. Quantitative results were obtained only when the reagent was strictly anhydrous and contained no more than about one part of anhydride per thousand parts of acetie acid (Table I). DETERMINATION OF ACONITIC ACID IN PRESENCE OF CITRIC ACID
Reagent. For 1 liter of reagent, dissolve 100 grams of dry potassium acetate crystah in 460 ml. of glacial acetic acid (99.6y0). Dissolve, by worming, 10 grams of boric acid in another 460-ml. portion of glacial acetic acid. Mix the two solutions, add 30 ml. of acetic anhydride, and reflux the mixture for one hour. Cool to room temperature and protect from absorption of moisture. Method. If the sample is not thoroughl dry, dissolve 1 to 2 grams in about 100 ml. of water, or if it is Hquid, take sufficient to contain a t least 1 gram of total acids and dilute to about 100 ml. Add sufficient sodium hydroxide solution or acetic acid to bring the solution to pH 6.0 to 6.2. Dilute with water to about 150 ml. and heat on the steam bath. Add with stirring 50 ml.
of saturated neutral lead acetate solution and cool. to room temperature. Collect the precipitate as described in the procedure for aconitic acid (6), dry thoroughly a t 120" C., and, using 100 ml. of the anhydrous boric acid-acetic acid reagent, decarboxylate for 1.5 hours according to the procedure of Roberts and Ambler ( 6 ) . Calculate the carbon dioxide evolved as aconitic acid. Results of several typical determinations are given in Table 11. If the samples to be analyzed are dry, decarboxylate 1 to 2 grams with the boric acid-acetic acid reagent directly, as in the aconitic acid procedure (6). Oxalic, galacturonic, and mucic acids are slowly decarboxylated with the boric acid-acetic acid reagent. LITERATURE CITED
(1) Boeseken, J., Rec. trap. chim., 37, 165 (1918). (2) Easterfield,T. H., and Sell, W. J., J . Chem. SOC.,61, 1003 (1892). (3) Kolthoff,M., Rec. trav. chim., 45, 607 (1926). (4) LaMer, V. K., and Greenspan, J., J . Am. Chem. SOC.,56, 1492 (1934). (5) Rath, J., Ann., 358, 98 (1908). (6) Roberts, E. J., and Ambler, J. A., ANAL.CHEM.,19, 118 (1947). (7) Zawidski, J., Roczniki Chem., 5, 511 (1925).
RECEIVED February 24, 1947. Agricultural Chemical Research Division, contribution No. 203.
Rapid Determination of Nitroglycerin and Ethyl Centralite in Rocket Propellant Powder I. S . HIRSCHHORN', Badger Ordnance Works, Baraboo, Wis. The use of 84% acetic acid makes pbssible the complete extraction of nitroglycerin and ethyl centralite from ground samples of double-base propellant powders in 20 minutes. The extracts are analyzed for nitroglycerin by a ferrous chloride-titanous chloride method and for ethyl centralite by a volumetric bromination procedure. The results obtained agree closely with those found by the regular 24-hour ether extraction procedure.
I
N CONNECTION with the manufacture of rocket propellant powders during World War 11, rapid control methods were needed, particularly for nitroglycerin and ethyl centralite. The standard analytical procedures are based upon ether extraction for as long as 72 hours. It was found that the nitroglycerin and ethyl centralite could be extracted by refluxing ground samples of powder with 84% acetic acid for 20 minutes. The two constituents could then be determined in the acetic acid solutions by the ferrous chloride-titanous chloride method of Becker (2) and the bromination method of Waugh, Harbottle, and Noyes ( 7 ) , respectively. A slight blank was necessary to correct for the solubility of nitrocellulose in 84% acetic acid. PROCEDURES
Reparation of Sample. Slice a wafer of rocket powder into thin slices and cut the slices into small chips (approximately 10 x 5 x 2 mm.). Carefully clean a Wiley mill, and place a small beaker under the lower vent. Be sure that the mill is vented at both top and bottom. Set the mill for operation a t medium speed. Replace the cover over the mill. Carefully mix all the chips together, and grind one chip a t a time until enough ground powder for the analysis has collected In t h e beaker. Preparation of Solvent Acetic Acid. Mix pure glacial acetic acid with distilled water in the ratio of 5 t o 1, using carbon dioxide as the mixing gas. Check the concentration of the acid by titration with standard base, and adjust if necessary to 84.0 * 0.5%. Extraction. Place a 1-gram sample (accurately weighed) of grouqd rocket powder in a 250-ml. Erlenmeyer flask provided 1
Present address, Chemistry Department, Drew University, Madison,
N. J .
with a ground-glass joint, add 50 ml. of 84% acetic acid (warmed to 100" C.), and mix the powder with the acid by swirling. (.A supply of hot 84y0acetic acid is maintained by heating the acid in a water bath, employing a reflux condenser to prevent changes in concentration.) Connect the Erlenmeyer flask t o a reflux condenser, and heat the flask in a boiling water bath for 20 minutes. Remove and cool the flask to room temperature in a cold mater bath. Disconnect the flask from the condenser. Filter the cooled extract through a KO.4 Whatman paper into a clean 750-ml. reduction flask. Carefully rinse the Erlenmeyer flask with 20 ml. of 84% acetic acid, and filter into the reduction flask. Repeat this procedure, using two successive 10-ml. portions of 84% acetic acid. For the ethyl centralite determination, filter the extract directly into a clean 250-ml. iodine flask. Nitroglycerin Determination. REDUCTION. Place glass beads in the flask, and connect to the carbon dioxide supply. Be sure that sufficient gas enters the flask to create a ripplr on the surface of the solution, and maintain this supply throughout _ _ . the titration. Add 30 ml. of 0.7 N ferrous chloride solution and 50 ml. of 1 to 1 hydrochloric acid, and swirl. Connect the reduction flask to an Allihn condenser. and boil the solution on a hot plate for 10 minutes. If brown 'fumes are observed in the condenser, discontinue the determination, since it will be in error. Cool the solution to room temperature in a cold water bath, rinse the reflux condenser with distilled water, disconnect the flask, and rinse the ground-glass joint. TITRATION. Titrate the solution with 0.25 N titanous chloride. After approxim'ately 50 ml. of titanous chloride have been added, add 5 ml. of 40y0 ammonium thiocyanate, and continue the titration until the color changes sharply from red to peach. BLANKDETERMINATION. Run a blank determination on the reagents, and apply the correction to the results obtained on a sample.
881
NOVEMBER 1947 Table I.
Precision of Nitroglycerin Determination on a Composite Lot of Rocket Powder
Weight of Sample Grams 1,0522 1,0597 1.0180 1,0070 1.0028 1,0088 1,0201 1.0120 1.0101 1,0670 1.0379 1.0071
N e t Volume of 0.2453 N TiCh
Piitroglycerin ’
M1. 73.29 73.68 71.06 70.25 69.88 70.51 71.30 70.51 70,28 74.54 72.51 70.09 Av.
% 43.11 43.03 43.20 43.17 43.13 43.26 43.26 43.12 43.06 43.22 43.24 43.07 43.16
Table 11. Precision of Ethyl Centralite Determination on a Composite Lot of Rocket Powder Weight of Gamde Grams 0,9940 1,0249 1.0398 1.0121 1.0716 1.0256 1.0060 1.0630 1.0030 1,0634 1,0254 1.0464
Net Volume of 0.0244 N NarS,Oa
Ethyl, Centralite
M1.
% 1.03 1.02 1.02 1.02 1.04 1.04 1.04 1.03 1.03 1.04 1.03 1.03 1.03
6.28 6.38 6.46 6.31 6.78 6.53 6.37 6.68 6.34 6.73 6.48 6.58 Av.
CALCULATION. Per cent nitroglycerin, =
2.523N(A - B )
WR
‘V = normality of titanous chloride A = ml. of titanous chloride for titration of sample B = ml. of titanous chloride for titration of blank W = dry weight of sample, grams R = per cent recovery expressed as a decimal fraction
Ethyl Centralite Determination. TITRATION.Add 25 ml. of 0.04 N potassium bromate-potassium bromide solution, measured from a buret, to the acetic acid extract, add 5 ml. of 1 t o 5 hydrochloric acid, stopper the flask, swirl for one minute, and add 5 ml. of 10% potassium iodide solution. Titrate the liberated iodine with 0.02 N sodium thiosulfate solution, adding 5 ml. of starch indicator solution near the end point. BLANKDETERMINATION. Run a blank on the reagents, using 25 ml. of the bromate-bromide solution, etc. CALCULATION. Per cent ethyl centralite =
6.704 N (A
- B)
W
with a ground-glass joint) containing 50 ml. of 84% acetic acid, then adding 0.5 gram of smokeless grade nitrocellulose, 0.03 gram of diethyl phthalate, and 0.01 gram of ethyl centralite. Mix these ingredients together by swirling. Connect the Erlenmeyer flask to a reflux condenser and follow the regular procedure for the extraction, reduction, and titration of nitroglycerin. Run a blank determination on the reagente only. Calculate per cent recovery as follows: Per cent recovery =
2.523N (A
- B)
W
N = normality of titanous chloride solution A = ml. of titanous chloride for titration of known sample B = ml. of titanous chloride for titration of blank W = grams of pure nitroglycerin in sample RESULTS
Tables I and I1 show the precision obtained by the foregoing procedures on a sample of rocket powder. Table I11 shows data on recovery of nitroglycerin obtained by the analysis of synthetic samples. Table I V shows a comparison of the results obtained by the regular ether extraction procedure end by the 84% acetic acid method.
Table 111. Determination of Nitroglycerin in Synthetic Powder Samples Weight of Sample Gram 0.4136 0.4438 0.4413 0.4453 0.4224 0.4468 0.4659 0.4198 0.4161 0.4199 0.4151 0,4306 0,4292 0.4166 0.4031
Net Volume of 0.27N TiCh M1. 61.23 65.66 65 41 66.31 62.86 66 34 69.01 62.41 61.89 62.62 61.86 64.26 63.55 62.32 59.86
Recovers
Av.
% 100.92 100.86 101.04 101.44 101,38 101.14 100.90 101.27 101.32 101.59 101.29 101 43 100.64 101,68 100.93 101.19
Table IV. Comparison of Ether Extraction and 84vo Acetic Acid Extraction Methods for Nitroglycerin in Rocket Powder Lot No.
3087 3903 3081 3088 3086
Ether Extraction 24 hours 72 hours
%
%
42.63 42.79 42.87 43.01 42.82
43.31 43.43 43.36 42.98 43.11
84% Acetic Acid Extraction % 43.08 43.12 42,67 43.00 42.88
N = normality of sodium thiosulfate solution
A = ml. of sodium thiosulfate for titration of blank B = ml. of sodium thiosulfate for titration of sample W = dry weight of sample, grams Standardization of Titanous Chloride. Several methods for standardization of titanous chloride are described in the literature. I n this work, the titanous chloride was standardized against pure iron wire, using the procedure outlined by Sutton (6) in which the iron is oxidized by hydrogen peroxide. Titanous chloride’may also be standardized against iron vvire by use of bromine and hydrochloric acid, as recommended by the American Society for Testing Materials (1). Per Cent Recovery of Nitroglycerin. Determine the nitrogen content of a sample of nitroglycerin by the standard Du Pont nitrometer method (3, 6). Determine the moisture content of the nitroglycerin by vacuum desiccation for 24 hours. Calculate the punty on a dry basis. Prepare a synthetic powder sample by weighing 0.42 t o 0.43 gram of the nitroglycerin into a 250-ml. Erlenmeyer flask (fitted
LU1 (the limit of’ uncertainty under ideal conditions) was calculated by the method of Moran (4). For the nitroglycerin determination, LU1 is *0.24% as given by the data of Table I. LU1 for the ethyl centralite determination as given by the data of Table I1 is +0.0247,. DISCUSSION
The separation of nitroglycerin from rocket powder is based upon the solubility of nitroglycerin and the relative insolubility of nitrocellulose in 847, acetic acid. The selection of 84y0 acetic acid in preference to other concentrations was for two main reasons: Extraction time is 20 minutes and results are equivalent to those obtained by ether extraction methods in 24 t o 72 hours. If 100% recovery were the main objective, it could be accomplished by use of 65% acetic acid
V O L U M E 19, NO. 1 1
882 and a relatively longer period of extraction (approximately 2 hours). The results in Table I11 are 1.2y0above the calculated values, but agree closely n-ith those obtained by the regular ether extraction method as shown in Table IV. The value of the recovery factor, R, may be readily determined by following the procedure outlined in this report. The recovery factor should be redetermined for each new formulation of powder. e
to J. B. R-eaver, director of the Chemical Engineering Laboratow, for advice and guidance. LITERATURE CITED
Am. SOC.Testing Materials, Tentative Recommended Practices E50-46T (1946). Becker, W.W., IKD.ESG. CHEM.,ASAL. ED.,5, 152 (1933). Davis, T. L., “Chemistry of Powder and Explosives,” pp. 271-3, Kern York, John Wiley & Sons, 1943. Moran, R. F., ISD.E K G .CHEM., ANAL.ED.,15, 361 (1943). Pitman, J. R., J . SOC.Chem. Ind., 19,982 (1900). Sutton, “Systematic Handbook of Volumetric Analysis,” p. 263, Philadelphia, P. Blakiston’s Son & Co., 1935. Waugh, T. D., Harbottle, G., and Noyes, R. M., ISD. ENG. CHEM., AKAL.ED.,18, 636-7 (1946).
ACKNOWLEDGMENT
The experimental work in this article was done in the Chemical Engineering Laboratory of the Badger Ordnance Works, operated by the Hercules Powder Company. The author is indebted
RECEIVED October 10, 1945.
Loss of Nitrate Nitrogen Caused by Chlorides Method f o r Determining Total Nitrogen PHILIP RIcG. SHUEY, Savannah, Ga. The Kjeldahl method is likely to give significantly low results when chlorides and nitrates are present in relati\ely large amounts unless the nitrogen content of the gases etolted before addition of the reducing agent is determined and added to the nitrogen obtained in the usual Kjeldahl procedure. The Deiarda method should be used when chlorides and nitrates are high and in the absence of cyanamide, urea, or organic material.
S
EVERAL methods for the determination of total nitrogen are
widely accepted as standard procedure. For the most part these are modifications of the well-known Kjeldahl method, involving digestion of the sample with concentrated sulfuric acid. With mixtures containing organic nitrogen-bearing materials the Kjeldahl-Gunning-Arnold ( 1 ) method, which involves digestion with concentrated sulfuric acid in the presence of a suitable catalyst, is in common use. en as organic I n mixtures containing nitrate nitrogen a nitrogen the sample is treated with concentrated sulfuric acid containing salicylic acid, and the nitro compound is reduced with sodium thiosulfate or zinc, as in the modified Kjeldahl method ( 3 ) . If nitrate nitrogen or nitrate nitrogen and ammonia nitrogen are the only forms present, the Devarda (4) method may be employed. This involves distillation of the sample in dilute sodium hydroxide solution with Devarda alloy, whereby both nitrate and nitrite nitrogen are simultaneously reduced t o ammonia and distilled along with any ammonia nitrogen which may have been present originally. This is an accurate and rapid method that is not affected by the presence of chlorides. I n the author’s laboratory, where mixed*fertilizersamples are continually analyzed, mixtures containing nitrates frequently show low values for total nitrogen. Investigation revealed’that this was repeatedly the case in mixtures containing both nitrate nitrogen and chlorides. Many fertilizers contain so little nitrate nitrogen that losses by the usual modified Kjeldahl procedure are of little importance ; however, for certain fertilizers relatively high in nitrate nitrogen the losses for nitrogen may reach significant proportions. Certain experimental work was undertaken to establish the validity of these observations and t o develop a method whereby nitrogen losses may be recovered. Although the work done in this laboratory pointed towards the recovery of nitrogen from certain fertilizer mixtures, the procedure recommended should find application in analytical laboratories where nitrogen determinations are made on materials other than those found in the fertilizer industry.
Table I.
.
Nitrogen in Mix‘tures Containing Potassium Sulfate (Series A)
Sample 1A
2A 3A 4A
70
70
2 14
2 11 2 99 4 02 4 94 5 93 10 16
3 4 5 6 10
5h 6A
Kjeldahl Method
Theory 05 04 02 01 05
Devarda Method
Difference between Methods
70 2 3 4 5 6 10
13 08 03 05 07 10
70 0 0 0 0 0 0
02 09 01 11 14 06
EXPERIMENTAL
In the Kjeldahl method, modified to include nitrate nitrogen, reactions involving nitrate nitrogen are represented as follows (6, 8) :I
I.
Salicylic Acid-Sodium Thiosulfate Method
+ &SO4 (KH,),SOa + 2HNO3 + 2CsH4:O H , COOH = 2CsH,. OH .,NOz.COOH + salicylic acid nitrosalicylic acid
2NH4SO3 2HSO3
2HzO
+ + 6H2S03+ 6s 6HzS03+ 2CsH3.0H.SOz.COOH+ 2H20 = 6H2S04 + 2CsH3,OH. YH?.COOH aminosalicylic acid 6Sa2S203 6H2SOa= 6SazS04
6s
+ 12HzSO4
11.
18SO2
+ 12H2O
Salicylic Acid-Zinc Dust Method
+ HZSO4 (SH,)zSO4 + 2HSO3 + 2C6H4.O H ,COOH 2C6H3,O H . SOz. COOH + 2H2O 6Zn + 6H2S04= 6ZnSOa + 12H 2XH4S03
2HxO3
