Determination of Total Volatiles in Smokeless Powder W. E. SHAEFER, ROBERT T. HALL, JOHN C. FRENCH’, AND WALTER W. BECKER Hercules Experiment Station, Hercules Powder Company, Wilmington 99, Del. In the manufacture of solvent types of smokeless powder, small amounts of volatiles (ether, alcohol, and water) remain in the finished powder. These volatiles may be determined accurately by dissolving 2-gram samples in dibutyl phthalate by overnight agitation at 85’ C., after which the samples are evacuated for 2 hours at a pressure of 5 mm., and the loss in weight of the system is then measured. In the analysis of certain types of smokeless powder, it is
necessary to dissolve the samples in an atmosphere of nitrogen to avoid oxidation, and to add more stabilizer to prevent decomposition. This method was used in all ordnance plants manufacturing smokeless powder during World War 11. The method appears to be applicable to the determination of any readily volatile substance in admixture with any nonvolatile heat-stable material soluble in a nonvolatile high-boiling solvent.
M
ETHODS of greater rapidity and accuracy than those previously available were needed for proper plant control in producing the enormous quantities of smokeless powder manufactured during World War 11. In the manufacture of solventtype powders, a small amount of total volatiles (ether, alcohol, and water) is retained in the finished powder. The determination of total volatiles is important because the amount present greatly affects the ballistic properties of the powder. Prior to 1940, the solution-precipitation method was the only one available for determining total volatiles. It was really an indirect or “difference” method which consisted of (1)extracting a weighed sample of powder with ether, (2) drying and weighing the ether extract, (3) dissolving the nitrocellulose residue from the ether extraction in ether-alcohol, (4)precipitating the nitrocellulose with water, ( 5 ) evaporating the latter mixture to dryness, and (6) weighing the residue. The difference between the weight of the sample and the sum of the weights of ether extract and dried nitrocellulose represented the total uolatiles. This difference value obviously included all the errors in the other determinations. The analyst needed considerable experience and patience to obtain concordant results. Depending on the type of powder, from 3 to 6 days were required to complete a determination. In 1940, an entirely new and direct method, hereafter termed the “solution-evacuation” method, was developed and has since been used for determining total volatiles in solvent-type powders. It consists essentially in dissolving (overnight) the sample in dibutyl phthalate a t 85” C., evacuating a t a pressure of 5 mm., and measuring the loss in weight of the system. The apparatus required is somewhat elaborate, but, once set up, one analyst can make 12 determinations per day. The method was used a t all ordnance plants manufacturing smokeless powder during World War I1 and was made available to our Allies. More recently, this general method has been applied to the determination of total solids in resin solutions (1). Many difficulties had to be overcome before the solutionevacuation method could be successfully applied to smokeless powder. Dibutyl phthalate was selected from various possible high-boiling liquids as the most satisfactory solvent. Suitable conditons had to be determined for dissolving samples of smokeless powder in dibutyl phthalate in a reasonable time without decomposition or oxidation of any components in the powdersolvent system. While preliminary work on solution temperature was done a t 100” C., subsequent work showed that 85’ C. was preferable. (This temperature was suggested by the Indiana Ordnance Works, operated by E. I. du Pont de Nemours and Company.) To make the method applicable to both single-base and nitroglycerin powders, the powder was dissolved a t 85 C. in an atmosphere of nitrogen, and an additional known amount of the stabilizer, diphenylamine, was added to react with oxides of 1 Present
nitrogen which might otherwise be given off during the long (16hour) heating period and cause fictitiously high Eesults. For the solution vessels, polarimeter-type tubes of about 100-ml. capacity proved most satisfactory. These were tilted back and forth mechanically inside an electric oven. The presence of steel balls in the tubes hastened the solution of the smokeless powder. To obtain results of satisfactory precision and accuracy, it was necessary to pretreat the dibutyl phthalate so as to ‘decrease its total volatiles content, to obtain blank values on the dibutyl phthalate, to A C “condition” the heavy solution tubes before weighFigure 1. Apparatus Solution tube, A . Protective drying tube, B . Counterpoise, C ECCE N T R l C
n
fl
1” Figure 2.
Rocking Mechanism and Manifolds Left, front view.
address, Hercules Powder Co., Kenvil, N . J.
378
Right, aide view
JUNE 1947
379
by gradually opening needle valve E. Remove the tubes from the oven, place them in a suitable tray, and imTO H Y V A mediately attach the small PUMP c protective drying tubes. Replace the latter with small cork stoppers after the solution tubes have cooled to room temperature. Weighing the Solution PYREX WOOL Tubes. Since this determination consists in the measurement of a decrease of 20 to 40 mg. in the weight of a 170-gram system, the conditioning and weighing proYREX WOOL cedures are important. Wipe the tubes with a wet towel and then with a clean dry cloth which is free of lint. Dl0UTYL P H T H A L A T E This operation serves to clean the tubes, remove electrostatic charges, and hasten the C ATMOSPHERE attainment of equilibrium with the moisture content Figure 3. Vacuuni Line .4ssenibly of the air. Allow the tubes to stand near the balance for a t least 30 minutes and weigh them, using a counterpoise (Figure 1) containing a suitable ing them, and to use a suitable counterpoise. Under the condinumber of steel balls, so that it will have approximately the same tions &ally established, known amountsof total volatiles weight, volume, and exterior surface as a solution tube containing had been added to knon-n mixtures of dry nitrocellulose, dinitroof dibutyl phthalate and 10steel balls. 50 toluene, and diphenylamine (simulating smokeless powder) were Determination of Total Volatiles. Remove the wads of Pyrex wool with pointed-tipped forceps, introduce 2-gram samples of determined with adequate accuracy and precision. Similar smokeless owder through a metal funnel, reinsert the wads of plant-produced samples were analyzed with equal precision. Pyrex woof weigh the tubes accurately, and attach them to the manifold in the electric oven. At least two of the tubes should be APPARATUS put in the oven without samples, in order that blank values on the dibutyl phthalate may be found simultaneously with the deter~i~~~~ sholvs a solution tube, A , in a wire holder, a protective drying minations of total volatiles. After alternately evacuating the drying tube, B , and a counterpoise, c. The tubes and filling them SlOwlY with nitrogen through stopcock F, tube, which contains indicating Drierite, to preventthe they are left full of nitrogen with stopcock F turned to connect the access of atmospheric moisture into a solution tube while it is oven with the tube leading to the nitrogen overflow bottle containcooling. Figure shows the mechanism and the arrangeing mercury. Admit air to the pressure regu1ator, pump, ment of the manifolds to which 16 solution tubes are attached. and the rest Of the system by opening stopcock 6 '. Rock the tubes The rocking mechanism causes the tubes to tilt back and forth a t 85' C. for a t least 15 hours. Ordinarily, the samples dissolve through an angle of approximately at the rate of 12 complete under these conditions. It is essential that they be softened by cycles per minute. The manifolds and solution tubes are mounted dibutyl phthalate, but not essential that they dissolve cominside an Oven (central scientific company, catalog No. 95, pletely. 105A). Figure 3 indicates the relative positions of the vacuum matter from the tubes by evacuation at Remove the pump, pressure gage, pressure regulator (S),and various traps. mm. for 2 hours. The beginning of the evacuation, while most of A suitable empty trap, cooled by dry ice, may be used instead of the volatile matter is being removed, is the critical point of the the one containing silica gel. determination. The pressure can be lowered rapidly to about 50 mm., but must be lowered cautiously from about 50 mm. to 5 REAGENT mm. over a period of approximately 10 minutes to prevent mechanical loss of the dibutyl phthalate solution. Remove the A good grade of dibutyl phthalate (odorless grade, Carbide tubes from the oven, attach protective drying tubes, and condiand Carbon Chemicals Co.) containing 0.1% of dissolved diphention and weigh the tubes in the manner already described. ylamine is used as a nonvolatile solvent. This is pretreated in the Calculation. solution tubes prior to weighing in the samples by evacuating it a t 85' C. and 1-mm. pressure for 2 hours. The pretreatment is conducted a t 1-mm. pressure instead of a t the 5-mm. pressure ( A + B, X loo = %total volatiles grams of sample used during the removal of total volatiles from samples to obtain lower and more uniform blank values. where A = decrease in weight of sample tube, and B = average change in weight of blank tubes. The change in weight of the PROCEDURE blank tubes is usually negative, but occasionally is positive, possibly due to humidity changes. In all cases the change is algePretreatment of the Reagent. Place 10 clean, dry steel balls braically to A * (0.78-cm., 6/ls-inch, diameter) in each of a series of solution tubes and then pour 50 ml. of dibutyl phthalate into each tube, using a DISCUSSION small funnel. After wiping the inlet of a tube with tissue paper, insert a Plug of Pyrex wool (about 0.2 gram) at such a Point that During the development of this total volatiled procedure, a considerable number of determinations were made to gain infor" , f & l l ~ n ~ ~ ~ ~~ $ k a ~ t ~ ~ ~ ~ ~ ~ mation as to the optimum conditions under which it should be serted later. performed. Only a few of these will be discussed. T h e n total httach the tubes to the manifold of the rocking device inside the oven by means of 5-em. pieces of clean rubber tubing. Close volatiles in both single-base and nitroglycerin powders were determined by heating a t 85 ' C., the results were the same, regardless ~ o ~ ~ ~ ~ , of 1% hether the samples were heated in dibutyl phthalate for 16 or turn on the rocking motor and vacuum pump, and evacuate the for 32 hours. This indicates that no decomposition with evolutubes a t 1 mm. or less as shown by the McLeod gage. This pretreatment procedure is accomplished very easily because the evaction of gases or vapors occurs lvhen the poivder is subjected to prouation is started when the dibutyI phthalate reagent is sti1I a t C,, on the other longed heating at this temperature. approximately room temperature. hand, the results were slightly higher on long heatlng (0.15% -it the end of 2 hours, stop the vacuum pump and rocking higher after an additional 16 hours, for example). At 70" C , motor, open stopcock B cautiously, and admit dry air slowly
:zl\ztzFey::: " ; n ~ ~ ~ " , " , z ~ ~ c ~ ~ ~ ~ ~ ~ s ~ ~ ~ ~~~~~~~
V O L U M E 19, NO. 6
380
Table I. Determination of Known Amounts of Volatile Matter Added to Dibutyl Phthalate, Nitrocellulose, and Nitroglycerin Mixtures Solution of Water, Alcohol and E t h & Added
Solution of Water, Alcohol and Acetdne Added
Mo.
MQ.
.. ..
.. ..
M1.
Nitrocellulose Added Grams
Xitroglycerin ildded Gram
Dinitrotoluene Added Gram
Diphenylamine Added Gram
50
..
..
.. .. 0.020 0.020 0.020 0.020 0.020 0.020
0.0 0.0 77.4
Dibutyl Phthalate
..
..
.. ..
1.1 1.1 1.1 1.1 1.1 1.1
0.41 0.75 0.41 0.54 0.69 0.87
0.10 0.10 0.10 0.10 0.10 0.10
Mg.
-
.
I
1.4 0.5 1.5
6i:3
Mo.
.. ..
..
1.8 0.9
.
.. ..
+- 00 .. 91
-1.4 -1.4 -1.4 -1.4 -1.4 -1.4
-78.2 -67.0 -50.4 -63.7
60:2
..
Mo
-
0.0 0.0
48: 1
Correction Value
Av.
50 50 50 50 50 50
Change in Weight
Difference between Volatiles Added and Found
Total Volatiles Found. Mo.
-0.9 1 -0.6 -0.6 +0.9 f1.0
+o.
76.8 65.6 49.0 62.3
Av.
0.7
Table 11. Analysis of Samples and Determination of Known Amounts af Added Total Volatiles by Evacuation at 5 RIm. and85 C.
Type of Powder Blank Blank
Wei h t 0%
Sample Grams
Change in Weight on Evacuation at 5 hlm. for 1 Hour
.. ..
M g.
%
Me.
%
- 1.0
.. ..
-6.5e -4.OC -5.3 -5.0 -4.7 -4.2
.. ..
+ 0.6 Av.
ddditiona! Total VolaChange in Total Volatiles tiles Found Weight on Fur- Found on Furafter Evacua- ther Evacua- ther Evacuation tion a t 5 Mm. tion a t 5 M m . a t 5 M m . for for 1 Hour for 1 Hour for 1 Hour
-
Single-base, small arms, lot 1
2.00 2.00 2.00
0.2 -33.4 -33.0 -33.5
Single-base, small arms, lot 2
2.00 2.00 2.00
-42.3 -42.2 -41.5
1.66 1.64 1.67 Av. 1 . 6 6 2.11 2.10 2.07 Av. 2 . 0 9
-4.8 -4.5 -4.6 -4.6
MO .
70
.. ..
.. ..
-0.02 -0.03 -0.06 -0.03 -0.04 -0.04
Total Volatiles Found after EvacuaTotal tion a t 5 mm. Volatiles for a Total Added a t of 2 Hoursa This Point
1VQ
-
..
1.64 1.61 1.61 1.62 2.08 2.06 2.03 2.06
Change in Weight on Evacuation a t 5 hlm. for 1 Houra
4212 48.3 47.9 46.4
Total Volatiles Found
Difference between Volatiles Added and Found
%
%
.
....
1.2 0.3
+ ++ 00 .. 64
..
..
..
..
-40.7
2:04
-0:07
-46.4 -47.1 -45.0
2.32 2.36 2.25
-0.10 -0.04 -0.07 -0.07
0 In this additional hour of evacuation, average loss in weight of bla,nka was slightly higher than that of samples. Therefore, amount of total volatiles found after eyacuation for 2 hours was apparently slightly,less than, b u t within limit of error of, amount found after 1 hour. b Prior to this treatment, tubes were filled with nitrogen a n d heated for 1.5 hours at 85O C. e Blank values higher than those usually obtained.
the 2.0-gram samples did not dissolve in 50 grams of dibutyl phthalate in 16 hours, and the solution was too viscous to permit free movement of the steel balls. On determining total volatiles in large samples (&gram) a t 85' C., the greater part of the samples did not dissolve. Horn-ever, the results were the same as when 2-gram samples were taken and completely dissolved. I n spite of this fact, it is considered preferable to have the samples dissolved completely prior to removal of the total volatiles by evacuation. All the available comparative results on smokeless powder samples indicate that the removal of total volatiles is usually complete when it is accomplished by evacuation a t 85' C. and 10 mm. for 1.5 hours or 5 mm. for 1hour. However, to assure complete removal of the total volatiles, the evacuation at 5 mm. should be conducted for 2 hours. In several determinations, the samples were dissolved in dibutyl phthalate in an atmosphere of oxygen instead of in nitrogen. This exaggerated the harmful effect attributed to oxygen that had been observed when samples were dissolved in the presence of air. When a n atmosphere of oxygen rn-as used, the results, expressed as per 'cent total volatiles, were 0.3 to 0.5 unit lower than when nitrogen was used. A satisfactory technique of cutting and sampling large-size grains of powder was developed in order to apply the method to cannon powders. A 16qnch paper cutter was provided with a perforated guide plate and gear arrangement, so that thin slices of large grains could be readily cut off. These slices were further subdivided with a pair of tinner's snips, and then kept in small stoppered weighing bottles until they could be weighed. The worth of the method was first demonstrated by the analysis of knowns. . Mixtures of dibutyl phthalate, nitrocellulose, nitroglycerin, dinitrotoluene, and diphenylamine were made up.
Table 111.
Determination of Total Volatiles in Check Samples of Smokeless Powder
Ordnance Laboratory
Lot A
Check Samples Small Arms Lot B
Multiperforated nitroglycerin
%
%
%
1.77 1.85 1.85 1.80 1.96 1.87
0.99 1.08 1.10 1.05 1.02 1.19
2.32 2:40 2 : id
..
Table IV. Comparison of Total Volatiles Results Found by Solution-Evacuation and by Solution-Precipitation Methodsa
Type of Powder 30-cal. 40-mm. 105-mm. howitzer 155-mm. un 155-mm. goaitzer 3-in. AA 37-mm. M 3
No. of Samples Analyzed 3 27 8 4 6
2 41
Average of Results BY By solutionevacuation method
precipitation method
Difference
%
%
%
1.42 0.94 1.08 1.86 0.84 1.70 1.82
1.30 1.01 1.08 1.85 0.86 1.62 1.74
-0.12 f0.07
*0.00
-0.01 +0.02 -0.08 -0.08
a Anal ses made a t Radford Ordnance Works, operated by Hercules Powder
60.
evacuated at 1 mm., and weighed. Known amounts of ether, alcohol, acetone, and water were added and the tubes were again evacuated and weighed. The results in Table I show that excellent recoveries of the added volatiles were obtained. After showing that the proposed method was satisfactory for synthetic mixtures, the next logical step would have been to
,
JUNE 1947
381
apply the method to an actual smokeless powder sample of known volatiles content. Unfortunately, it 1% as impossible to prepare such a sample. Therefore, a plant sample of powder was first dissolved in dibutyl phthalate, evacuated for 1 hour a t 5 mm. to remove the volatiles already present, and weighed, and the total volatiles were calculated as show-n in Table 11. The triplicate results thus obtained TTere concordant. Further evacuation for an additional hour under the same conditions had a negligible effect upon these results. Known amounts of ether, alcohol, and water were added and the tubes were again evacuated and weighed. The agreement between the volatiles added and found was as good as that previously obtained in the analysis of synthetic mixtures. Therefore, it was concluded that the use of a temperature of 85" C., a pressure of 5 mm., and a time of 2 hours was satisfactory. Table I11 shows the average results found when three check samples were analyzed in six ordnance laboratories. Although the variation among these results is greater than that observed in any single laboratory, the concordance among them is considered satisfactory. A comparison of results found in one laboratory by the solution-evacuation and precipitation methods is CORtained in Table Is'. The maximum difference between average results found by the two methods when applied t o 91 samples is
0.12%. However, the weighted average difference is only 0.027c, which is negligible. A consideration of the results of replicate determinations on hundreds of samples by the solution-evacuation method indicates that these results, expressed as per cent total volatiles, have an accuracy of a t least 0.20% and a precision of 0.10%. The average value for standard deviation, calculated in accordance with the equation of Moraii ( 2 ) from the results found when t v o samples were analyzed 14 and 15 times, respectively, is 0.04'%. As has been pointed out ( I ) , this general method can he used for the determination of any readily volatile substance in admixture with ani' nonvolatile heat-stable material. ACKNOWLEDGMENT
The authors wish to acknowledge the assistance of Harold M. Spurlin in devising and constructing the first apparatus which embodied the principle of the solution-evacuation method. LITERATURE CITED
(1) M c K i n n e y , C. D., Jr., Turk, E., a n d Shaefor, W. E., ISD. Erio. C H E M . , -4XAL. ED.,18, 14 (1946). (2) Moran, R. F., Ibid., 1 5 , 361 (1943). (3) K e w m a n , M . S., Ibid., 12,274 (1940).
Determination of Sulfur by Combustion in a Vertical Tube DUDLEY B. H.IGERRI.AN, Socony-Vacuum Laboratories, Socony-Vacuum Oil Co., Znc., Research and Development Department, Paulsboro, N. J . A method is described w-herein sulfur is determined in a wide range of organic liquids by allowing the sample to drop into a verticall?.held tube containing a bed of hot porous material. The resulting sulfur gases are draw-nfrom the lower end of the tube and are absorbed in a solution of hydrogen'peroxidein which the sulfur is determined alkalimetrically. Rapidity, accuracy, and simplicity are among the advantages of the new method.
S
EVERBL accurate and reliable methods for the determination of sulfur in organic compounds are in common use. The Carius ( 5 ) ,Parr oxygtn bomb ( I ) , and peroxide bomb (6) methods all give dependable results, but the number of steps involved presents numerous opportunities for error and consumes much valuable time. Considerable success has also been claimed for the Braun-Shell method (S),wherein the sample is placed in a heated quartz tube and slowly ignited, the combustion products being absorbed in a suitable solution. Still another method suggests burning the sample in a lamp after blending with a sulfur-free, low-boiling solvent (4). Sumerous other methods have been devised, none of which provides the simplicity, rapidity, and accuracy of the new method described here. This method yields results which agree well with theoretical values on pure chemical compounds. With oils and synthetic additives, the values agree with those obtained by the Parr oxygen bomb method. A single sulfur determination can be completed by the new method in 20 to 30 minutes. When a multiple unit apparatus was used (Figures 4 and 5 ) with two operators sharing the work, forty-eight sulfur determinations were completed in an 8-hour working day. APPARATUS
The apparatus required consists of a tube of stainless steel, 3 mm. thick and 370 mm. long, with a 25-mm. inside diameter, t o one end of which is welded a stainless steel tube, 1.5 mm. thick and 230 mm. long, with a 6.5-mm. inside diameter (Figure 1). At the other end of the 25-mm. tube are attached outwardly two small metallic wings or shoulders placed a t right angles to the tube and opposite each other. These serve as supports by which the tube is suspended in an electric furnace and also as a base for attaching the springs which hold the glass chimney in position.
This combustion tube is packed with quartz beads, or a suitable inert substitute, and coarse, clean sand supported a t the bottom of the tube by a perforated disk. The iroportion of beads t o sand is approximately 5 to 1 in six or eight alternate layers, starting with 80 mm. of beads a t the bottom and leaving 150 mm. of unfilled tube a t the top. The beads should not be over 5 mm. in diameter and the sand should be 20- to 40-mesh. The furnace consists of a core of stainless steel, 3 mm. thick, and 430 mm. long, vith a 38-mm. inside diameter. One end of this core is welded to the center of a circular disk of sheet iron, 3 mm. thick and 250 mm. in diameter, with a 12.5-mm. hole in its center. To the opposite side of the disk are welded three legs 230 mm. long which support the furnace and combustion tube in a vertical position. The core is wound with 12.8 meters of KO.19 Nichrome V resistance wire which is first coiled t o form a helix havine a 4.&mm. diameter and then covered with fishspine interlockiig ceramic insulators (Figure 2). A heating element so designed will carry a current of 600 to 650 watts. The core is insulated with 50 mm. of Super X, then 50 mm. of 85% magnesia, and finally a thin layer of flaked asbestos and cement. Thirty millimeters of insulation are affixed to the bottom of the furnace. A 6.5-ohm slidebar rheostat is placed in the circuit as a means of adjusting and controlling the furnace temperature. Optimum operating temperature is 1526' F. 4 furnace so constructed (Figure 3) can be operated continuously a t the required temperature for a t least 6 months. The loT-ier or exit. end of the combustion tube is connected by means of a short piece of rubber tubing to the type of absorber described by A.S.T.M.(2). At the top of the tube is mounted a Pyrex chimney, 25 mm. in inside diameter and 150 m. long, slightly flared a t the bottom and having two hooks diametrically opposite each other, t o which are attached two small springs connecting with the combustion tube t o hold the chimney firm. A mirror held above the furnace at the proper angle permits the operator to observe the interior of the tube. The dropper from which the sample is automatically fed into the combustion tube is made by drawing out the end of a piece
