I Darwin 8. Dah1 and Peter F. Lott Chemistry Department University of Missouri-Kansas City Kansas City, Mo. 64110
“H
ERE’S THE PROBLEM.
we an?behg sued for
millions because this black-mwder rmn blew UD. We are certain smokeless powder used, Gut how & we show it? Our situation is made worse by the fact that we did not test-fire the gun WOEit left the plant. You how,of c o w , that the U.S. has no proof laws. I how, I how, don’t tell me -we should have proof-iked the gun. The c r u d point in the litigation is whether or not smokeless powder was used.’’ black powder, could be loaded with smokeless powder, which develops excessive pressure upon firing and blows up the gun. Or the hobbyist may intentionally use a “duplex” load, a mixture of black and smokeless powder, either to improve the ballistic characteristics or to reduce the amount of fouling left in the gun. Or, one might think that any gun of modern manufacture would be safe with smokeless powder and that the type of gunpowder used, as long BS it looked black, was irrelevant. The outcome of such errors can be long remembered, quite expensive, and devastating both to the injured party and the manufacturer of the firearm if litigation ensues.
With the present renewed interest in pioneer activities, such lawsuits are not rare occurrences, and injuries to the shooter can be very severe. Before the problem can be solved, we need information about the chemical content, appearance, and characteristics of black powder and smokeless powder. To the chemist, black powder is that mixture containing 75%potassium nitrate, 12.5%charcoal, and 12.5%sulfur. To the uninitiated it might simply be any gunpowder that looks black and that perhaps can be purchased relatively cheaply at a garage sale. Consequently, entirely through circumstances of chance and ignorance, it is quite possible that this recreational device, designed to use only 446A
ANALYTiCAL CHEMISTRY. VOL
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Thus, the analytical problem is how to check both the remains in the powder flask and the residue left in the gun for either smokeless powder, black powder, or a mixture that might consist of black powder and smokeless powder. Immediately we recognize that there is not going to be much residue and that, if at all possible, the testing should be performed by two independent methods so as to produce unquestioned results. Ideally, the initial screening should also be quickly performed using a simple method with minimum equipment. One of the first questions to be considered is whether black powder varies considerably from manufacturer to manufacturer. Since it is composed of crystalline constituents, it should give an X-ray diffraction pattern. Furthermore, X-ray diffraction can be applied to the analysis of small amounts of material, and the diffraction pattern for a substance provides an unquestioned identification. Consequently X-ray diffraction patterns were recorded for several black powders as well as for a recently developed blackpowder-type propellant made for use in black-powder guns, Pyrodex. The superimposed diffraction patterns for current as well as several older black powders are shown in Figure 1. Mili0003-2700/85/0357-440A$01.50~0
0 1985 American Chemical Society
and Smokeless Gunpowders tary black-powder cartridges, which can be relatively easily obtained from cartridge collectors,were taken apart; some of the black powder WBS finely ground to obtain the diffraction patterns. Surprisingly, very little change was seen in the patterns for black powders currently made compared with those made more than 100 years ago. Nor did it seem to make much difference where the ammunition was
manufactured, and neither did age seem to change black powder. Obviously, an analysis for trace components would show differences, but overall the composition of the black powders, except for Pyrodex, is equivalent. Black-powder formulations that use sodium nitrate or ammonium nitrate instead of potassium nitrate do exist, and some contain no sulfur. These compwitions are seldom used
in firearm ballistic formulations because such mixtures are more difficult to ignite. Of interest are the compositions of several older gunpowders, shown in Table I. In contrast, smokeless powder, a nitrocellulose, does not give a diffraction pattern. To the trained eye, smokeless powder has a different appearance than black powder. It also has a distinctly different hardness. Figure 2
Nineteenth-century hammer-type Parker shotgun after smokeless powder wm fired in the gun ANALYTICAL CHEMISTRY, VOL. 67, NO. 9, MARCH 1985
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shows a 3X magnification of several smokeless gunpowders and black powder. Thus by simple visual examination it may be possible to distinguish black powder from smokeless powder and to separate the individual components physically for further testa; black powder has the appearance of miniature lumps of coal. One flake of smokeless powder gives enough material for several chemical tests, and visual examination could also serve as one identification. Were we to check for the presence of smokeless powder, our initial aim would he to detect nitrocellulose or the distinctive additives in smokeless powder. Finding nitrocellulw might be questioned, as a number of consumer products, for example, certain fingernail polishes as well as wood finishes, may contain nitrocellulw. Consequently, one would also determine the stabilizers in gunpowder, the most common of which is diphenylamine, which is present at the 1-2% level. Nitrocellulose powders are a colloided nitrocellulose. If they are double-based powders, nitroglycerin has been added. In its manufacture the finished smokeless powder is often glazed with graphite, which gives it a black appearance. Graphite glazing is performed to stabilize the moisture content of the powder and lessen the absorption of moisture, as well as to make the powder electrically conductive 80 as to minimize dangers in blending from static electricity. This black appearance can be a major cause of a person assuming that any gunpowder that is black is black powder. Spot tests Where might you f i d a flake of smokeless powder? In the powder flask,the container used to dispense the desired amount of gunpowder. Take the flask apart; carefully examine any crevice where a particle might be caught as well as any threaded parts, as flakes might be trapped between the threads. If a flake of smokeless powder is recovered, it can be dissolved in acetone or methylene chloride, and its infrared (IR) spectrum can be run. Or, colorimetric spot tests can be used. Surprisingly, black powder is virtually insoluble in acetone. In contrast, smokeless powder is quite soluble. Thus treatment of the material with anhydrous acetone provides an excellent separation. We were first made aware of this procedure through a private communication from John A. Reffner of American Cyanamid Research Laboratories. The acetone extract can now be tested for the presence of nitrocellulose by its reaction with certain chromogenic reagents such as chromotropic acid or, interestingly, diphenylamine. A few drops USA
ANALYTICAL CHEMISTRY, VOL. 57, NO. 3, MARCH 1985
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in black powder and not in nitrocellulose powders, can also he performed hy t r a n s f e w some of the residue to a teat tube and adding a small amount of benzoin. A piece of lead acetate paper is fued over the mouth of the tuhe, and the teat tube is inserted into a glycerin bath (a beaker filled with glycerin) heated to 130 ‘C. The temperature is raised to 150 ‘C. Formation of a black precipitate of lead sulfide on the paper is a positive teat for sulfur and indicative of black powder.
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of the acetone extract are transferred to a spot plate, and the solvent is carefully evaporated using a gentle stream of air. The renidue is reconstituted with five d r o p of concentrated H&O,. Three drops of a 100-ppm solution of diphenylamine in concentrated HSO, are added to a separate compartment ofthe spot plate, and then one drop of the reconstituted gunpowder solution is added. A pOaitive teat for nitrocellulose is a change
from clear to blue. If the sample has a large amount of diphenylamine in it already the addition of the sulfuric acid suffices for the color change. A positive teat is certainly indicative of the presence of smokeleas powder, although not conclusive in it8elf. Further quick verification can he made hy adding a few d r o p of this acetone extract to a microscope slide and allowing it to evaporate. A white spot appears; if it is nitmcellulose it often gives a lacelike pattern when examined under a microscope at 100-fold magnification, as shown in Figure 3. A quick spot test for black powder can he made hy adding a few drops of the 100-ppm diphenylamine solution to the residue left from the initial acetone extraction. Formation of a blue color indicatea the presence of black powder. ntrading black powder with acetone and then testing this acetone extract with the diphenylamine reagent invariably shoWe4 no color reaction with the diphenylamme reagent. Accordingly, three independent teata can he done quicklq visual examination of the m a t e d , m i m p i c examination, and color testa in a spot plate. A teat for sulfur, an ingredient
Tertlng the sun Although fiiding flakes of smokeless powder in the powder flask would he quite fortunate, it still does not give pmof that the smokeless powder was fired in a gun. Thus, teata need to he performed on the gun itself. The same spot teata can he used.Depending on the situation, portions of the debris in the gun can he scraped out, then treated with acetone as in the previously described procedure. Or parta ofthe guncan he immersed in an acetone solution in a beaker, which is placed in an ultrasonic cleaner. The acetone solution is partially evaporated, and the color teata and microscopic examination for nitrocellulose previously described are performed. The residue from the acetone extraction is treated with water and teated for the presence of potassium nitrate using the diphenylamie teat previously described. Or the residue may he collected and an X-ray diffraction pattern can he taken. The advantage of this approach is that the X-ray diffraction pattern is defiitive, nondestructive, and leaves the sample available for further testing. The major interest, obviously, is in the detection of smokeleas powder. If the teats so far are inconclusive, chance are that the amounta present are very small, and instrumental methods must he used. Conventional
Flguro 2. Maaophotosaph(3X) of black powder and &in smokeless
Flguro 8. Photomlcrogaph(1OOX) of nitrocellulose ANALYTICAL CHWSTRY. VOL. 57, NO. 3, MARCH I985
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ANALYTICAL CHEMISTRY. VOL. 57. NO. 3, MARCH 1985
Flgure 4. Chromatogram of (a)smokeless powder and (b) black powder
IR or NMR measurements would probably not be a worthwhile effort because the concentrations are too small. Mass spectrometry may work; the appearance of a peak for diphenylamine would he conclusive proof. Using gas chromatography to detect traces of powder residue can be difficult. Furthermore, because of the number of peaks that may be obtained, a positive identification based only on a gas chromatographic pattern could he questioned. High-performance liquid chromatography could offer a reasonable possibility. The optical detectors, such as the UV detector, probably will not show sufficient sensitivity and may be bothered by the presence of interferences in the sample matrix, such as fragments of the finish from the gun stock. An electrochemical detector, however, can provide additional selectivity and sensitivity. The separation can be obtained quite quickly and easily; picogram amounts of diphenylamine can be determined. One disadvantage is that the method will not pick up the “centralites,” substituted phenyl ureas added in some smokeless gunpowders as stabilizing agents.
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They are used much less commonly than diphenylamine. We are currently working to extend the detection approach to the centralites. With electrochemical detectors, one would gain additional selectivity and sensitivity over optical detectors. In using a conventional electrochemical detector, a hydrodynamic voltammogram needs to be constructed first to obtain proper operating conditions for the detector. The normal procedure is to set the voltage on the detector to a fixed value, inject the sample, and when the peak appears for the desired constituent, measure the peak height, finish the separation, and inject the next samples with the detector set at successively higher voltages. This is quite time-consuming. One simple solution to the problem is to prepare a stock solution of diphenylamine in the same eluting solvent as is used for the chromatographic separation. Pour this solution into a buret and connect the plastic tubing that enters into the flow cell to the buret tip. Control the buret to deliver a slow, continuous flow of solvent with the stopcock. Preferably, the flow should be the same as that which might be used in the separation, for example, 1mL per minute. Change the voltage, measure the recorder de-
-
flection, and repeat. Because it is a polarographic procedure, it is really rather similar to obtaining a polarogram with a manual polarograph. Because an oxidative mode of detection is used, we selected acetone as the major component in the mobile phase rather than methanol-which was used by other investigators-due to acetone’s greater stability toward oxidation. This makes it easier to determine diphenylamine and increases the sensitivity of the method. A typical chromatogram for smokeless powder, showing the diphenylamine peak, is presented in Figure 4. The peak was verified as diphenylamine by the collection of a sample and by running its mass spectrum. Furthermore, linear calibration curves can be obtained by varying the concentration of diphenylamine, so that a quantitative determination of the amount of diphenylamine can be obtained. Thus in many cases simple visual observation, chemical tests, and instrumental methods can be used to obtain irrefutable evidence as to whether or not smokeless powder was used in a black powder gun. In addition there is one other simple examination that may provide additional information. Look at the injured party.
The powder burns of black powder differ from those of smokeless powder. A black-powder discharge throws out very small particles of carbon that tattoo the skin. The carbon hembedded in the skin and may take years to go away. The burns are quite visible for about 6 years and may possibly still be seen 10 or more years later. Embedded particles of smokeless powder are more gray than black and will disappear much more quickly, possibly within a year. The information obtained by observation of the powder burns may not be conclusive, but could certainly aid in confirmation,
Acknowledgment We thank John C. Cayton and Stephen C. Warlen of the Kansas City Regional Criminalistics Laboratory, Kansas City, Mo., for their assistance in providing ruptured firearms and photographs. This work was presented at the Benedetti-Pichler Symposium of the American Microchemical Society, held at the Eastern Analytical Conference, New York City, November 1984. The detailed procedure for obtaining hydrodynamic voltammetry plots is scheduled to appear in the April issue of the Microchemical Journal.
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#-
CONTENTS __ ~
ACS Symposium Series NO. 191 George C.Levy, Editor Syracuse University Based on a symposium jointly sponsored by the divisions of Analytical, Organic, and Physical Chemistry of the A CS.
UltraHigh-Field NMR NMR Spectroscopyat600MHz Two-dimensional Fourier Spectrosco y Quadruoolar Metallic Nuclei Deuterium NMR gpectroscopy Metabolism of ’3C Labeled Substrates Chemical Bond Labeling and Double-Cross Polanzation NMR NMR Spectroscopy at High Pressure 8 13CCross Polarization MaglcAngleSpinnln NMReNMRof LinearandC CIIC Peptides 3’P NMR 8tudies 13C NMR Studies of 6NA Dynamics Photo-Chemically induced Nuclear Polariz a t m of Biolooical Molecules 13CNMR CharacterizaGonof Solid Fossil Fuels Polyester Thermoplastic Elastomers 23NaNMR Studies
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ANALYTICAL CHEMISTRY, VOL. 57, NO. 3, MARCH 1985
