The Analytical Approach Darwin B. Dahl and Peter F. Lott Chemistry Department University of Missouri—Kansas City Kansas City, Mo. 6 4 1 1 0
The Differentiation of Black We are being sued for Λ Λ millions because this black-powder gun blew up. We are certain smokeless powder was used, but how can we show it? Our situation is made worse by the fact that we did not test-fire the gun before it left the plant. Ifou know, of course, that the U.S. has no proof laws. I know, I know, don't tell me —we should have proof-fired the gun. The crucial point in the litigation is whether or not smokeless powder was used." • • T L I E R E ' S THE PROBLEM.
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 in formation about the chemical content, appearance, and characteristics of black powder and smokeless powder. T o t h e chemist, black powder is t h a t mixture containing 75% potassium ni trate, 12.5% charcoal, and 12.5% sul fur. To the uninitiated it might simply be any gunpowder t h a t looks black and t h a t perhaps can be purchased relatively cheaply at a garage sale. Consequently, entirely through cir cumstances of chance and ignorance, it is quite possible t h a t this recrea tional device, designed to use only 446 A ·
black powder, could be loaded with smokeless powder, which develops ex cessive pressure upon firing and blows u p the gun. Or the hobbyist may in tentionally use a " d u p l e x " load, a mix ture of black and smokeless powder, ei t h e r to improve the ballistic charac teristics or to reduce the a m o u n t of fouling left in the gun. Or, one might think t h a t any gun of modern manu facture would be safe with smokeless powder and t h a t the type of gunpow der used, as long as it looked black, was irrelevant. T h e outcome of such errors can be long remembered, quite expensive, and devastating both to the injured p a r t y and t h e manufacturer of the firearm if litigation ensues.
ANALYTICAL CHEMISTRY, VOL. 5 7 , NO. 3, MARCH
1985
T h u s , t h e analytical problem is how to check both the remains in t h e pow der flask and the residue left in the gun for either smokeless powder, black powder, or a mixture t h a t might con sist of black powder and smokeless powder. Immediately we recognize t h a t there is not going to be much resi due and t h a t , if a t all possible, the testing should be performed by two independent methods so as to produce unquestioned results. Ideally, the ini tial screening should also be quickly performed using a simple method with m i n i m u m equipment. One of the first questions to be con sidered 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. Further more, X-ray diffraction can be applied to t h e analysis of small amounts of material, and t h e diffraction p a t t e r n for a substance provides an unques tioned identification. Consequently X-ray diffraction p a t t e r n s were re corded for several black powders as well as for a recently developed blackpowder-type propellent made for use in black-powder guns, Pyrodex. T h e superimposed diffraction patterns for current as well as several older black powders are shown in Figure 1. Mili0003-2700/85/0357-446A$01.50/0 © 1985 American Chemical Society
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and Smokeless Gunpowders t a r y black-powder cartridges, which can be relatively easily obtained from cartridge collectors, were taken apart; some of t h e black powder was finely ground to obtain the diffraction pat terns. Surprisingly, very little change was seen in the p a t t e r n s for black powders currently made compared with those made more t h a n 100 years ago. Nor did it seem to make much difference where the ammunition was
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manufactured, and neither did age seem to change black powder. Ob viously, a n analysis for trace compo n e n t s would show differences, b u t overall t h e composition of the black powders, except for Pyrodex, is equiv alent. Black-powder formulations t h a t use sodium nitrate or a m m o n i u m ni t r a t e instead of potassium nitrate do exist, a n d some contain no sulfur. T h e s e compositions are seldom used
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in firearm ballistic formulations be cause such mixtures are more difficult t o ignite. Of interest are the composi tions of several older gunpowders, shown in Table I. In contrast, smokeless powder, a ni trocellulose, does n o t give a diffraction p a t t e r n . To t h e trained eye, smokeless powder has a different appearance t h a n black powder. It also has a dis tinctly different hardness. Figure 2
powder was fired in the gun
ANALYTICAL CHEMISTRY, VOL. 57, NO. 3, MARCH 1985 · 447 A
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Figure 1. X-ray diffraction patterns (instrument response vs. 2(9 value) for modern black powders and black powders from antique rifle cartridges (a) Pyrodex powder, U.S. manufacture, 1984, (b) Goez black powder, U.S. manufacture, 1983, (c) 10.75 X 58 Russian Berdan cartridge, 1884, (d) 11 X 59R French Gras cartridge, 1874, (e) 0.56-56 U.S. Spencer cartridge, 1862 448 A · ANALYTICAL CHEMISTRY, VOL. 57, NO. 3, MARCH 1985
shows a 3X magnification of several smokeless gunpowders and black pow der. Thus by simple visual examina tion it may be possible to distinguish black powder from smokeless powder and to separate the individual compo nents physically for further tests; 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 smoke less powder, our initial aim would be to detect nitrocellulose or the distinc tive additives in smokeless powder. Finding nitrocellulose might be ques tioned, as a number of consumer prod ucts, for example, certain fingernail polishes as well as wood finishes, may contain nitrocellulose. Consequently, one would also determine the stabiliz ers 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 dou ble-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 conduc tive so as to minimize dangers in blending from static electricity. This black appearance can be a major cause of a person assuming that any gun powder that is black is black powder. Spot tests Where might you find a flake of smokeless powder? In the powder flask, the container used to dispense the desired amount of gunpowder. Take the flask apart; carefully exam ine any crevice where a particle might be caught as well as any threaded parts, as flakes might be trapped be tween the threads. If a flake of smoke less powder is recovered, it can be dis solved in acetone or methylene chlo ride, and its infrared (IR) spectrum can be run. Or, colorimetric spot tests can be used. Surprisingly, black pow der is virtually insoluble in acetone. In contrast, smokeless powder is quite soluble. Thus treatment of the materi al with anhydrous acetone provides an excellent separation. We were first made aware of this procedure through a private communication from John A. Refiner of American Cyanamid Re search Laboratories. The acetone ex tract can now be tested for the pres ence of nitrocellulose by its reaction with certain chromogenic reagents such as chromotropic acid or, inter estingly, diphenylamine. A few drops
Table I. Percentage composition of black gunpowders * Type
Potassium nitrate
Charcoal
8th century, Marcus Graecus 8th century, Marcus Graecus c. 1252, Roger Bacon 1350, Arderne (laboratory recipe) 1560, Whitehome 1560, Bruxelles studies 1635, British government contract 1781, Bishop Watson
66.66 69.22 37.50 66.6 50.0 75.0 75.0 75.0
22.22 23.07 31.25 22.2 33.3 15.62 12.5 15.0
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11.11 7.69 31.25 11.1 16.6 9.38 12.5 10.0
in black powder and not in nitrocellu lose powders, can also be performed by transferring some of the residue to a test tube and adding a small amount of benzoin. A piece of lead acetate paper is fixed over the mouth of the tube, and the test tube is inserted into a glycerin bath (a beaker filled with glycerin) heated to 130 °C. The tem perature is raised to 150 °C. Forma tion of a black precipitate of lead sul fide on the paper is a positive test for sulfur and indicative of black powder. Testing the gun
•" Davis, Tenny L. "The Chemistry of Powder and Explosives, Vol. I"; John Wiley and Sons: New York, N.Y., 1941; p. 39.
of the acetone extract are transferred to a spot plate, and the solvent is care fully evaporated using a gentle stream of air. The residue is reconstituted with five drops of concentrated H 2 S0 4 . Three drops of a 100-ppm so lution of diphenylamine in concen trated H2SO4 are added to a separate compartment of the spot plate, and then one drop of the reconstituted gunpowder solution is added. A posi tive test for nitrocellulose is a change
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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 test is certainly indicative of the presence of smokeless powder, al though not conclusive in itself. Fur ther quick verification can be made by adding a few drops of this acetone ex tract to a microscope slide and allow ing it to evaporate. A white spot ap pears; if it is nitrocellulose it often gives a lacelike pattern when exam ined under a microscope at 100-fold magnification, as shown in Figure 3. A quick spot test for black powder can be made by adding a few drops of the 100-ppm diphenylamine solution to the residue left from the initial ace tone extraction. Formation of a blue color indicates the presence of black powder. Extracting black powder with acetone and then testing this acetone extract with the diphenylamine re agent invariably showed no color reac tion with the diphenylamine reagent. Accordingly, three independent tests can be done quickly: visual examina tion of the material, microscopic ex amination, and color tests in a spot plate. A test for sulfur, an ingredient
Although finding flakes of smoke less powder in the powder flask would be quite fortunate, it still does not give proof that the smokeless powder was fired in a gun. Thus, tests need to be performed on the gun itself. The same spot tests can be used. Depend ing on the situation, portions of the debris in the gun can be scraped out, then treated with acetone as in the previously described procedure. Or parts of the gun can be immersed in an acetone solution in a beaker, which is placed in an ultrasonic cleaner. The acetone solution is partially evapo rated, and the color tests and micro scopic examination for nitrocellulose previously described are performed. The residue from the acetone extrac tion is treated with water and tested for the presence of potassium nitrate using the diphenylamine test previ ously described. Or the residue may be collected and an X-ray diffraction pattern can be taken. The advantage of this approach is that the X-ray dif fraction pattern is definitive, nonde structive, and leaves the sample avail able for further testing. The major interest, obviously, is in the detection of smokeless powder. If the tests so far are inconclusive, chances are that the amounts present are very small, and instrumental methods must be used. Conventional
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Figure 2. Macrophotograph (3X) of black powder and certain smokeless powders (a) Black powder, (b) Alcan AL-7 smokeless pow der, (c) Hodgdon H110 spherical smokeless pow der, (d) Du Pont No. 4759 extruded smokeless powder
Figure 3. Photomicrograph (100X) of nitrocellulose ANALYTICAL CHEMISTRY, VOL. 57, NO. 3, MARCH 1985 · 451 A
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Figure 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 be 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 be 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.
They are used much less commonly than diphenylamine. We are currently working to extend the detection ap proach 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 so lution 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, 1 mL 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. Be cause 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 oxi dation. This makes it easier to deter mine 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 col lection of a sample and by running its mass spectrum. Furthermore, linear calibration curves can be obtained by varying the concentration of diphenyl amine, so that a quantitative determi nation of the amount of diphenyl amine can be obtained. Thus in many cases simple visual observation, chemical tests, and in strumental methods can be used to obtain irrefutable evidence as to whether or not smokeless powder was used in a black powder gun. In addi tion there is one other simple exami nation that may provide additional in formation. Look at the injured party.
Hazards in the Chemical Laboratory
CONTENTS
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We thank John C. Cayton and Ste phen 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 Soci ety, held at the Eastern Analytical Conference, New York City, Novem ber 1984. The detailed procedure for obtaining hydrodynamic voltammetry plots is scheduled to appear in the April issue of the Microchemical Journal.
This 17-chapter volume outlines some of the more recent NMR applications. The development of methodology to obtain high resolution NMR represents one of the promising new areas of research. At the same time, the FT technique makes high resolution experiments much easier tobe performed at high pressure. The 13C NMR experiments of rhodium carbonyl clusters presented in this text are an illustrative example of the application of this tech nique to homogeneous catalytic pro cesses. The nature of solid fossil fuels is probed with high resolution FT NMR using cross-polarization and magic angle spin ning techniques. Two-dimensional FT NMR and the new information this techni que can provide also are discussed. CONTENTS
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Acknowledgment
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The powder burns of black powder differ from those of smokeless powder. A black-powder discharge throws out very small particles of carbon that tat too the skin. The carbon is embedded 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 disap pear much more quickly, possibly within a year. The information ob tained by observation of the powder burns may not be conclusive, but could certainly aid in confirmation.
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 ACS.
Ultra High-Field NMR · NMR Spectroscopy at 600 MHz • Two-dimensional Fourier Spectroscopy · Quadrupolar Metallic Nuclei · Deuterium NMR Spectroscopy · Metabolism of 13 C Labeled Substrates · Chemical Bond Labeling and Double-Cross Polarization NMR · NMR Spectroscopy atHigh Pressure » ,3 C Cross Polarization Magic Angle Spinning NMR · NMR of Linear and Cyclic Peptides · 31Ρ NMR Studies · 13C NMR Studies of DNA Dynamics · Photo-Chemically Induced Nuclear Polari zation of Biological Molecules · " C NMR Characteriza tion of Solid Fossil Fuels · Polyester Thermoplastic Elastomers · 23Na NMR Studies 388 pages (1982) Clothbound LC 82-11458 ISBN 0-8412-0723-2 US & Canada $54.95
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