and vapors, the list of ninhydrin reacting materials is reduced to those having significant vapor pressure a t ambient conditions. The work of Hnrding and Warneford (S), which demonstrated reaction viith RCH2HX2-and RCHNH2type bases, coupled with available vapor pressure data should allow potential users of the method to screen their system for possible interference. K i t h proper calibration, the technique should be applicable to other one- and two-component ninhydrin-reacting systems. The method has b e w applied successfully to the submarine atmosphere problem and appears to be the simplest
means available to separate and determine simultaneously occurring ammonia and RIE.4. Auxiliary Equipment. Simplicity of operation and dependable accuracy prompted the development of a device to expedite the sampling of the large volumes of air required by this method of analysis. It consists of a vibrator type diaphragm pump, a valved flowmeter, and a timing mechanism containing a cutoff switch for automatic run termination. These components are housed in a box equipped with appropriate connectors for sample attachment. This unit controls flow rates of 200 to 1200 ml. per
minute for times up to 1 hour Rith automatic shutdown and unattended operation. Commercial models of this unit are available (1). LITERATURE CITED
(1) American Instrument Co., Silver Spring, Md., patent applied for by U. S.
Naval Research Laboratory.
(2) Harding, V. J., MacLean, R. AI., J . Biol. Chem. 2 5 , 3 3 7 (1916). (3) Harding, V. J., Warneford, F. H. S., Ibid., p. 319. (4)McCaldin, D. J., Chem. Revs. 39, 60-1
(1960).
( 5 ) Ruhemann, S., J . Chem. SOC.98, 2026
(1910); 99,792 (1911). RECEIVEDfor review July 28, 1961. Accepted December 7 , 1961.
Spectrophotometric Determination of Inorganic Nitrate in Propellants GEORGE NORWITZ Pitman-Dunn laboratories, Frankford Arsenal, Philadelphia 37, Pa.
A method is proposed for the determination of inorganic nitrate in propellants. The sample is dissolved in acetone, the solution filtered, and the nitrate determined in the residue by the ferrous sulfate colorimetric method. The conditions for the development of the color were studied.
for the determination of inorganic nitrate in propellants (6, 9) involve many operations. The determination of inorganic nitrate salts i n propellants is performed ordinarily by analyzing for the cation (potassium, barium, and occasionally sodium) ( 4 ) . Such a method has the disadvantage that the assumption must be made that the salt is present as the nitrate. The quantitative determination of inorganic nitrate by use of the pink color obtained m-ith ferrous sulfate in concentrated sulfuric acid solution has been described by English ( 2 ) and Swann and Adams (8). English pipetted a 2-ml. aliquot into 1 ml. of water, added 1 ml. of a solution of ferrous ammonium sulfate in 1 to 5 sulfuric acid. followed by 25 ml. of 5 to 1 sulfuric acid. Swann and Adams added alkali to a solution of the nitrate, evaporated to dryness, and added 20 ml. of a solution of ferrous sulfate in 3 to 1 sulfuric acid. Bandelin and Pankratz (1) and Semel, Laccetti, and Roth ( 7 ) applied the method of Swann and Adams to the analysis of nitrate esters and nitramines, respectively. ETHODS
RECOMMENDED PROCEDURE
Ferrous sulfate solution. Dissolve 2 grams of ACS grade FeS04. 7H20 in 30 ml. of water containing a few drops of concentrated sulfuric acid. This sulfuric acid is necessary to prevent air-oxidation of the ferrous ion. Add 100 ml. of concentrated sulfuric acid and cool to room temperature. Prepare this reagent fresh daily since FeSOc precipitates on standing overnight. Standard potassium nitrate solution No. 1 ( I ml. = 0.1 mg. Koa-). Dry ACS grade KT\'O3 in an oven a t 12.5" C. for 2 hours. Dissolve 0.1630 gram in water and dilute to 1liter in a volumetric flask. Standard potassium nitrate solution No. 2 (1 ml. = 0.1 nig. KKOa). Dissolve 0.1000 gram KKOa in water and dilute to 1 liter in a volumetric flask. Powminco acid-washed Gooch asbestos (Central Scientific Co.). Preparation of Calibration Curve. Pipet lo-, 20-, 30-, 3 5 , and 40-ml. aliquots of standard potassium nitrate solution KO.1 into 250-ml. beakers and add 8 drops of O.1N sodium hydroxide solution from a dropping bottle. Carry along a blank sample prepared by adding 8 drops of the alkali to 25 ml. of water. Evaporate to dryness on the hot plate. Add 3.0 ml. of water with a pipet and swirl to dissolve the salts. Cool t o below room temperature in a n ice bath. Add 10 ml. of concentrated sulfuric acid from a IO-ml. tall-type graduate. When the solutions have cooled to room temperature, remove the beakers from the ice bath, and add 10 ml. of ferrous sulfate solution measured with a graduReagents.
ate while swirling. Decant the solutions into 25-ml. volumetric flasks that have been rinsed with 10 to 3 sulfuric acid. Wash the beakers with sufficient 10 to 3 sulfuric acid to bring the volumes in the volumetric flasks to 25 ml. Shake, and allow to stand for 10 or more minutes. Measure the transmittance a t 520 mp in a spectrophotometer that has been set to 100% transmittance with the reagent blank. Plot milligrams of Nos- against per cent transmittance. Method. Weigh the sample into a 250-ml. Erlenmeyer flask (with a ground glass stopper) t h a t has previously been dried in a n oven and allowed to cool. For 0 to 0.4% NO3use a 0.5-gram sample; for more than 0.4% NOS- use a 0.3 gram sample. Add 25 ml. of acetone, stopper, and allow to stand overnight a t room temperature. Do not swirl the flask during the solution process, since particles of propellant may adhere to the sides of the flask. Prepare a moderately thick asbestos pad in a 25-ml. Coors No. 3 Gooch crucible, using Powminco acid-washed Gooch asbestos. Wash the pad by filling the crucible three times with water a t 9.5' to 100" C. The last portion of water should take about 7 to 8 seconds to drain. If the filtration time differs much from this, remove the pad and make a new one. Remove the Gooch and holder, and discard the water in the suction flask. Wash the holder and suction flask thoroughly with acetone. If there is water in the flask during the subsequent filtration of the acetone solution, a coating of nitrocellulose will form which will be difficult to remove. VOL. 34, NO. 2, FEBRUARY 1962
0
227
Place the Gooch and holder back into the suction flask which is protected by a safety trap. Wash the pad with a small amount of acetone. Swirl the acetone solution of the sample and filter. R'ash down the sides of the flask with 3 ml. of acetone from a n all-glass wash bottle with a fine tip and decant into the Gooch. Wash down the sides of the Gooch thoroughly with acetone. Do not wash the Gooch again. Wash down the sides of the Erlenmeyer flask four more times with 3-ml. washings of acetone (no more), and decant into the Gooch after each washing, allowing the
Table 1.
Type M5b
previous washing to drain before adding the next. Remove the Gooch and place it on a surface not attacked by acetone. Retain the Erlenmeyer flask. Pour out the contents of the suction flask, and wash the holder and suction flask thoroughly with acetone, and then with water. Place the Gooch and holder back into the suction flask. Add several portions of water at 95" to 100" C. to the original Erlenmeyer flask, transfer to the Gooch, and filter. Use a total of 100 t o 125 ml. of water. If less than 1.4% KOsis present, wash the filtrate into a 250-
Results for Inorganic Nitrate in Propellants
Kominal Inorganic Sitrate Content ( % ) 0.75 zk 0.25 KNOa, 1.4 i~0 . 2 Ba(K03)2
NOaFound
I
