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INDUSTRIAL AND ENGINEERING CHEMISTRY
accurately weighing and measuring vases of the type shown in the plate. These articles weigh about 170 grams, have an averagc wall thickness of 0.15 to 0.17 inch and are 6 inches high. The followiiig results have been obtained: 1. Water a t 100” F., no change in height or \veight 2. Out-of-door standing, no change 3 . Air oven a t 140’ F., 5% Iyeight loss, 3% height loss
Castings from the AB-500-5 formula do not crack after being repeatedly dropped on a concrete floor. The AB-500-1 ester yields compositions which are much less shock resistant. I casting made a t 175’ C. in an 8 X 8 inch metal form showed a shrinkage of 0.005 inch per inch. These compositions should be of use on short runs of molded articks and in the making of foundry patterns.
Vol. 43, No. 5
LITERATURE CITED
(1) Gardner, H. A., a n d Sward. G . G., “Physical a n d Chemical Examination of P a i n t s , Varnishes, Lacquers, and Colors,” 10th ed., p. 164-6, Bethesda, Md., H e n r y A. Gardner Laboratory, Inc., 1946. (2) hfalm, C. J., N a d e a u , G. F., and Genung, I,. R.,IXD. ENG. CHEX, ANAL.ED.,14,292-7 (1942). (3) Malm, C. J., Kelson, H . B . , a n d H i a t t , G . D., IND.E N G . CHEM., 41, 1065--9 (1949). (4) Malm, C. J., Salo, M., and Vivian, H . F., I b i d . . 39, 168-74 (1947). (5) M o d e m Plastics, 27, 70 (1960). (6) P r u d d e n , G . H . , Machi?bery, S. Y., 50, No. 11, 136-45 (July 1944). (7) Wagner, It. H., a n d Russell, J., IND.EXG.CHEM.,4 N A L . ED.,20, 151-5 (1948). RECEIVED August 29, 1950. Presented before the Division of Paint, Varnish, CHEMICAL and Plastic8 Chemistry a t the 118th Xeeting of the AXERICAN SOCISTP,Chicago, 111.
Exdosive Sensitivitv of Ammonium I Nitrate-Hvdrocarbon Mixtures J
J
3IELVIN A. COOIC AYD EUGENE L. TALBQT University of Utah, Salt Lake C i t y , U t a h T h i s study was undertaken to elucidate for the common good one of the aspects of the explosive hazards involved i n as a the commercial use of ammonium nitrate-e.g., fertilizer-when coated with various hydrocarbon waxes. It is shown that the maximum (cap and propagation) sensitivity occurs in mixtures of ammonium nitrate coated with 0.75 to 1.5% wax. A No. 6 blasting cap was found adequate to detonate the (fine-grained) coated ammonium nitrate product containing 0.75 to 1.5c/t wax. Moreover, with this wax content ammonium nitrate is capable of propagation indefinitely i n 1.875-inch diameter
charges. Unfortunately, this is also the desirable wax content required for satisfactory moisture resistance, antisetting, and free flowing properties of animoniuni nitrate. I n fact, even the most sensitive coarse ammoniuni nitrate-wax compositions are comparatively insensitive and unlikely to explode when properly handled. However, i n comparison with inorganic coated-e.g., lrieselguhr--or pure ammonium nitrate, they are tremendous13 more sensitive and likely to explode under provocative conditions, as when large quantities are involved in a fire.
E
consequence of this is that the ordinary air-gap sensitivity test is of no value in this case except possibly in very large diameterse.g., 6 inches. Those familiar with the problem of determining the explosive sensitivity of such mixtures usually confine their mertsurements to the following:
XPLOSIVE sensitivity may be defined as the relative ease of producing an explosion or detonation in an explosive substance. This definition, however, isimpracticalwithoutaleospecifying in detail the methods employed in producing the explosion, because sensitivity varies in an unpredictable manner from one method of initiation t o another. Fundamentally, an explosion is probably always the direct result of heat and, in principle, follows conventional reaction rate theory (6, 7 , I f ? ) . However, so many nontractable factors are involved in heat production in the many methods of initiation that one cannot yet provide a common theoretical basis of comparison of the various conditions known to produce explosions. I n lieu of an adequate theory t o evaluate the efficiency of the various methods of initiation as a source of heat, in producing explosions, it is necessary, in estimating hazards involved in the manufacture, transportation, and use of explosives, t o evaluate a w 9 l e series of sensitivities including all conceivable means by which explosions may be initiated. The case of ammonium nitrate-hydrocarbon mixtures provides a special problem in explosive sensitivity. Because of the relatively very low sensitivity of such mixtures, positive results generally are obtained only in a limited number of the standard sensitivity tests-for example, such mixtures usually will not explode in ordinary impact, friction, flame, spark, and shock tests. Moreover it is usually difficult t o obtain propagation in small diameters with almost any ammonium nitrate-combustible mixture t o say nothing of ammonium nitrate-hydrocarbon mixtures which are among the least sensitive mixtures of such combinations. The
1. Heat sensitivity or the determination of the rate of decomposition as a function of trmperature and the “explosion temperature. ” 2. The critical diameter of propagation with an adequate booster under controlled conditions-e.g., constant density, particle size, composition, and confinement. 3. The minimum size booster required to produce detonation of charges of constant size, length, confinement, composition, and particle size, etc. 4. Large diameter air-gap sensitiveness tests.
A “minimum primer sensitiveness” test is described for measuring the sensitivity of very insensitive explosives which, while not described previously in the open literature, has been used extensively in this and slightly modified forms in the explosives indust r y t o rate insensitive explosives of this type. It is supplemented t o a limited extent herein by a crude propagation sensitivity test. T h e effect of small percentages of solid hydrocarbon on the sensitivity of ammonium nitrate has been noted previously by Cook ( 2 ) and b y Nuckolls (IO). Cook, in fact, mentioned that solid hydrocarbon up t o 1%was a more effective sensitizer for ammonium nitrate than an equal percentage of T N T .
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1951
1099
MATERIALS AND MIXlNG PROCEDURES
~
49
I n addition to composition, the sensitivity of ammonium nitrate-hydrocarbon mxtures depends t o an important extent on the ammonium nitrate grist or article size. Mixing procedures employed here were designex t o maintain this factor as nearly constant as possible in any particular series. The ammonium nitrate for each series was taken from the same lot, and preheated to 85" C. in an oven. The hydrocarbon was melted separately to a fluid state and sprinkled into the hot ammonium nitrate. All compositions including those in which no hydrocarbon coating was added were mixed 45 minutes in an 8-inch diameter ball mill which was rotated at a velocity of 72 r.p.m. (While a ball mill is not ordinarily used and is not the best equipment for the formulation of compositions of this sort, it was employed here simply as an expedient in lieu of more desirable mixing equipment. It is believed, however, that adequate control was maintained in the present studies to minimize the disadvantages of the ball mill.) A constant mixing time of 45 minutes was selected to allow the composition to cool during mixing to below 35" C. The ball load in the mill was maintained constant throughout a given series. I n one series (series A) steel balls were used as follows: l/&inch, 5OO!l grams; This charge l/z inch, 4000 grams; 1 inch, 9500 grams of balls. was not considered t o be very efficient for grinding, but was employed in series A t o ensure uniform mixing. All other series were mixed in the ball mill employing a ceramic ball load as follows: inch, 200 grams; 1/2 inch, 1000 grams, 1 inch, 3000 grams. The number of ceramic balls in a particular size corresponded t o the number of steel balls of that same size. While this load produced less grinding, it gave adequate mixing in all cases. Mixings were made in 1500-gram lots in series A and B (except for B-4 and B-5 which were made in 2000-gram lots) and in 2000-gram lots in series C. Series A employed a No. 3 grade ammonium nitrate (0.1770 moisture, 1.0% inorganio coating, ,designated as sample A) and equal parts of paraffin, rosin, and petrolatum (1:l:l). The paraffin-rosin-petrolatum was varied from 0 t o loyo. The powder was cartridged in 17/8 (diameter) X 5'/8 inch (long) cardboard tubes at a density of 265 * 5 grams per cg. (1.03 grams per cc.). The temperature of the powder when packed was 30 * 5" C. Series B was made with Sample A-No. 3 amnionium nitrate (same grade as in series A). In this series, the hydrocarbon content was held constant at 1.0%. Several different hydrocarbons were used including paraffin (B-1); petrolatum (B-2); paraffin-rosin-petrolatum (1:2:1), (B-4); ( l : l : l ) , (B-3); paraffin-rosin-petrolatum (2: 1:l), (B-5). This series was carried out t o show the effect of the nature of the hydrocarbon coating. Each composition was cartridged a t 265 * 5 grams per cg. at a temperature of 30 * 5" C. Series C was made with a No. 2 ammonium nitrate (coarse) which contained 0.43% rosin, 0.1% paraffin, 0.08 , moisture, and 0.92% inorganic coating as received (sample BY Paraffinrosin-petrolatum ( 1 : l : l ) was used in all except the first composition of the series; in this composition the ammonium nitrate
TABLE11. EXPLOSIVE SENSITIVITY Composition No. Ammonium nitrate, % Paraffin-rosin-petrolatum (1:1:1), % Minimum primer test l i / r (dia.) X 8 inch-60% straight dynamite I l / r X 2 inch-straight dynamite l i / r X l/e inch-straight dynamite 15-No. 6 caps 10-No. 6 caps 8-No. 6 caps 6-No. 6 caps &--NO. 6 caps 4-No. 6 caps 3-No. 6 caps 2-No. 6 caps 1-NO. 6 CaDs Propagation teit li/r X 4 inch-60% straight dynamite primer
A-la 100.0 0.0 2F
... ... ...
A-10 99.25 0.75
... ...
...
...
...
... ...
... ... ...
... ... ... ... ...
...
'F. F
BD,OF
... ...
... D' ... 2D . I
..
%
Mesh Size
f36 35 to 48 48 t o 65 65 to 100 100 to 150 150
-
Loss
... ... ... ...
... 2D
5D, OF
Sample Sample A A-2 A-8 B-2 B C-3 2 . 4 3 % 1 . 2 5 1 . 0 5 0 . 9 4 88.65 2 1 . 6 7 3.28 0.00 2.27 0 . 9 4 6 . 8 3 14.03 38.83 4 . 3 1 20.66 13.83 3 . 0 5 25.00 41.38 25.38 33.62 39.44 0 . 9 8 13.89 14.08 36.77 35.71 43.36 0 . 4 9 15.27 0.00 3 2 . 3 1 5 . 9 2 0 . 3 7 0 . 0 0 9 . 7 2 0.00 0.00 0.87 1.12 0 . 0 0 0 . 4 1
C-7 28.64 18.43 16.58 13.06 17.59 3.52 2.18
C-8 41.28 13.08 14.62 10.90 18.23 1.28 0.51
alone-i.e., as received-was used. Hence, the first composition was really arffi-rosin-petrolatum (0.1:0.43:0). I n order t o reduce grmgng the ceramic ball load was used in this series and the mixes were made in 2000-gram lots. While grinding was much reduced in this series, the product was still somewhat h e r than the original ammonium nitrate. This, of course, was intentional in view of the restricted size of the charges used in these tests (the coarse product was not expected t o propagate in %inch diameter or less). The powder was cartridged at 30 5" C. a t a density of 265 * 5 grams per cg. Table I presents typical screen analyses of the ammonium nitrate as received and several selected compositions. The effect of hydrocarbon concentrations on grinding may be seen by comparing A-2 and A-8 or C-3, C-7, and C-8. As would be expected, the higher hydrocarbon content prevented grinding to some extent and gave a slightly coarser product. The effect of hydrocarbon on grinding was most pronounced in the f35 and -150 mesh sizes. A comparison of the effect of steel versua ceramic load is illustrated by A-2 and B-2. The particle size of series B compares favorably with series A, havlng approximately the same hydrocarbon content. TESTS OF EXPLOSIVE SENSITIVITY
The sensitivity of the various mixtures was determined by a minimum primer test using No. 6 blasting caps and in the case of insensitive compositions b y using various lengths of 1.25-inch diameter, 60% straight dynamite primed with one No. 6 cap. Detonations and failures were recorded by means of 1.5 (diameter) X 3 inch lead blocks, generally protected from direct detonation contact with the cartridge b y 0.5 (thick) X 3 X 3 inch steel plates. When detonation was complete the lead block was comt o 3/4 inch. When a partial detonation or compressed from plete failure was obtained no lead block depression resulted (even if the partial was a near detonation) and the bottom of the cartridge was generally found undisturbed. Figure 1 shows a comparison among depression results obtained with various ammo-
NITRATE-PARAFFIN-ROSIN-PETROLATUM COMPOSITIONS
(Series A) A-3 A-11 99.0 98.75 1 .o 1.25
A-2 99.5 0.5
2D F 2F F
...
OF - b 4 M O N I U M
TABLE I. TYPICAL SCREENANALYSES OF AMMONIUM NITRATE SAMPLES A ~ AMMONIUM D NITRATE-HYDROCARBON MIXTURES
.
.
A-4 98.5 1.5
A-5 98.0 2.0
...
...
...
...
... ...
I
... ...
...
... ... ... ... ... ... ... ...
... ...
2D
... ... 2D
...
6D, OF
... ...
... ...
...
... ... ... ...
3D
F, D 5D, OF
A-6 97.0 3.0
A-7 96.0 4.0
A-8 94.13 5.4
...
...
D
D
...
2D
2D
..
.F. .
F
D' ... D
..
D' D 2D F
5D, OF
... ... ...
... .FF. .
... ...
... ...
... ...
8D, OF
... ...
A-9 90.0 10.0 2F
... ... ... ...
... ... ... ... ...
... 1 . .
2D,4F
a A-1 was subjected to the same treatmen: as al1,other compositions even thou h no paraffin-rosin-petrolatum was added. Ir Sample A-No. 3 ammonium nitrate (1% inorganic coating). Mixings were ma% under constant conditions in ball mill with limited steel ball load. Fortyfive minutes mixin time, cartridge density, 1.03 g./cc. F = failure. = detonation. Number of lartridges detonating and number failing in propagation test.
8
1100
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 43, No. 5
t:
Figure 1. Minimum Primer Test, Showing Effect of Steel Plate, Detonation us. Failure, and Composition of Explosive, on Lead Block Depression Reading from top ito bottom 1. 1.25 X 4 i n c h straight dynamite on 0.5-inch steel First row. plate 2. Result of detonation in setup 1 3. Same as 1 without steel plate 4. Result of 3 Second row. 5. Cartridge of a m m o n i u m nitrate-hydrocarbon with 2-inch dynamite primer, no steel plate 6. 5.4'70 paraffin i n a m m o n i u m nitrate s e t u p 5 7. Same as 6 with steel plate Third row. 8. Cartridge of a m m o n i u m n i t r a t e h y d r o c a r b o n with 1-inch dynamite primer, steel plate 9. Ammonium nitrate plus 0.43'70 hydrocarbon, s e t u p 8 detonation 10. Ammonium nitrate plus 5.4Q hydrocarbon, s e t u p 5 , 1-inch dynamite, F failure
nium nitrate-hydrocarbon mixtures and 6OY0 straight dynamite. This gave an approximate measure of the strength or impulse of the detonation of ammonium nitrate-hydrocarbon mixtures compared with that of a strong commercial explosive. ( A correction for charge diameter would be required for accurate comparison.) The effect of the steel plate between the lead and the cartridge and the effect of the strength of the primer are also shown. The steel plate had an appreciable effect on the amount and nature of the depression. The strength of the primer had very little effect, except, of course, to determine whether detonation or failure occurred. The effect of the strength of the different ammonium nitrate-hydrocarbon mixtures mas only slightly apparent. The depression produced with 11/* X 4 inch-GO% straight dynamite primer was greater than in any of the ammonium nitrate-hydrocarbon compositions except the 5.470 hydrocarbon composition, although the difference between the 0.43%
F o u r t h row.
11. Assembly for m i n i m u m
No. of caps for detonation test Ammonium n i t r a t e plus 1.43% hydrocarbon, s e t u p 11, three No. 6 caps (D) 13. Same as 12, showing compression of lead 14. Ammonium n i t r a t e plus 1.43 qo hydrocarbon, t h r e e No. 6 caps, primer, F 15. Ammonium nitrate plus 1.43'70 hydrocarbon, one No. 6 cap, F 16. Ammonium n i t r a t e plus 1.43% hydrocarbon, 1i n c h dynamite, five, four, a n d t h r e e KO. 6 caps, left t o right 17. S e t u p 5, compositions P-1, P-3, P-5, P-6 (0.5, 1.0, 1.5, a n d 5.4% HC, respectively)
12.
Fifth row.
hydrocarbon and 5.4% hydrocarbon was not large. It was impossible to obtain detonations n i t h pure ammonium nitrate in 17/s-inch diameter, even with the finest ammonium nitrate product (A-1) and the strongest booster (1.25 X 8 i n ~ h - 6 0 7straight ~ dynamite). (The maximum effective primer length in these tests is actually only about 4 inches, longer lengths being ineffective.) I n the minimum primer test, attempts were made wherever possible to obtain the minimum number of No. 6 caps or the minimum length of 60% straight dynamite for a t least two successive detonations. The ability of a composition to propagate through five or more cartridges placed end to end was determined in a number of cases. Generally-, one finds that explosives which will shoot in l'/s-inch diameter with less than about 25 grams of GOY0 straight dynamite as the primer will propagate satisfactorily in a long column in this diameter. Any composition which detonated completely in the
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
May 1951
TABLE 111. EFFECT OF COMPOSITION OF HYDROCARBON COATINQIN 99% AMMONIUM NITRATE-1% HYDROCARBON COMPOSITIONS (Series B)
Minimum primer I, 4-NO. 6 cam
Propagation l'/r X 4 inch60 straight dynamite primer
...
,..
...
Complete ( 5 cg.)
Complete (7 cg.)
Complete (5 og.)
2D
Complete (4 cg.)
Complete (3 cg.)
a Sample A. No. 3 ammonium nitrate (same as in series A). Mixed in 2 to 1500-gram l o b in cases of B-1, B-2, and B-3, and in 1- to 2000-gram loto each in the cases of B-4 and B-5. Mixing time 45 minutes. Ball mill load, ceramic balls, same in all cases. F = failure; 6 = detonation.
*
minimum primer test with less than 15-No. 6 caps propagated through at least five cartridges in the propagation test, but those that required more than 25 grams of 60% straight dynamite failed to propagate using a l 1 / 2 X 4 inch (about 100 grams)-60% straight dynamite booster. Incidentally, for a comparison of cap versus dynamite priming, it was verified as illustrated in series A t h a t a l l / p (diameter) X 11/*inch charge of 60% straight dynamite (about 12 grams) was at least as strong as a bundle of 15 No. 0 caps as a primer. RESULTS OF TESTS
*
z
1101
ammonium nitrate which was a coarse grade ammonium nitrate. Mixing conditions were adjusted to give a minimum grinding and to produce a coarser grist of ammonium nitrate than in series A and B. While the C series ended up a much coarser product than either the ,4 or B series, enough grinding actually took place t o make it still considerably finer than the original No. 2 ammonium nitrate. Table IV gives the results of tests with series C. It is a n interesting fact that series C compositions containing 0.43% hydrocarbon and 3.0 t o 5.4 hydrocarbon were less sensitive than the comparable compositions in series A showing the desensitizing effect of coarse ammonium nitrate. However, those containing from 1.0 t o 2 . 0 % h y d r o c a r b o n (paraffin-rosin-petrolatum) were apparently as sensitive as the most sensitive in any of the other series despite the coarser product. DISCUSSION O F RESULTS
T h e explosive sensitivity of ammonium nitrate is almost invariably increased by incorporating in it small percentages of combustible materials. This sensitization of ammonium nitrate is effected by the increased heat made available in the explosion of ammonium nitrate-fuel mixtures by the reaction of the excess oxygen of ammonium nitrate with the combustible On the other hand, combustibles differ considerably in their ability t o sensitize ammonium nitrate. This may be a result of (1) differences in the fuel value of the combustible-Le., in the amount of heat generated by the fuel reaction with ammonium nitrate, and (2) physical characteristics of the combustible such as its lubricating or abrasive properties-factors which influence sensitivity of ammonium nitrate by controlling the amount of heat generated by tribochemical reactions such as those required in the initiation of detonation by shocks. It is the opinion of the authors that the behavior of ammonium nitrate-hydrocarbon-HC mixtures observed here may be explained as follows: hydrocarbons such as paraffin, petrolatum, Nujol, paraffin-rosin-petrolatum mixtures, and other waxes have a relatively large fuel value and thus a large tendency to sensitize ammonium nitrate (factor 1). However, they also have very
The results of the tests of series A are given in Table 11. As mentioned above, ammonium nitrate (A-1) containing no hydrocarbon was treated the same as all other mixings even though no paraffin-rosin-petrolatum was added in the A-1 mixings. Therefore, the ammonium nitrate particle size was comparable in all compositions of series A. Compositions A-1 (0% hydrocarbon) and A-9 (10% hydrocarbon) both failed with an l * / d X 8 inch60% straight dynamite primer. A very sharp maximum sensitivity occurred at 0.75 t o 1.5% paraffin-rosin-petrolatum; the compositions containing 0.75, 1.0, 1.25, and 1.5% paraffin-rosin-petrolatum all shot consistently with one No. 6 cap. The oxygenbalanced composition (A-S), while stronger on a weight basis than any of the others, as verified by the lead block depressions, was much less sensitive than those showing the maximum sensitivity. All the comTABLEIV. EXPLOSIVE SENSITIVITYOF COARSEAMRIOSIUM positions in series A from 0.5 t o 4.0% paraffinNITRATE-PHENOL-ROSIN-PETROLATUM COMPOSITIONS rosin-petrolatum propagated satisfactorily through (Series C) five or more cartridges. Composition No. C-2Ba C-3 C-4 C45 C-6 C-7 C-8 T h e primary sensitizing effect of paraffin-rosinAmmonium nitrate,O yo 99.57 99,O 98.5 88.0 97.0 96.0 94.6 Paraffin, % 0.1 0.33 0 . 6 0.66 1.0 1.33 1.8 petrolatum is its fuel value. Consequently one Rosin, Yo 0.33 0.33 0.5 0.66 1.0 1.33 1.8 .,. 0.33 0.5 0.66 1.0 1.33 1.8 Petrolatum, % would not expect much difference in sensitization Minimum primer test between the various hydrocarbon wax materials 11/4 X 8 inch-60% F ,.. ... ... ... ... 2F available. However, to test this, series B was straight dynamite l l / r X 6 inch-60% F . . . . . . . . . . . . . . . ... carried out in which several different wax coatings straight dynamite 1'/4 X 8 inch-@O% F ,.. ... ... ... ... 17 were employed. T h e results obtained in series B straight dynamite are given in Table 111,and show that the differences l l / r X 1 in~h-607~ F ... ... ... D D ... straight dynamite ... in sensitization of ammonium nitrate among ... ... ... l ' / r X l/z inoh-60% ... 2D 2F .straight dynamiti paraffin, petrolatum, and paraffin-rosin-petrolatum ... ... 10-No. 6 caps 8-No. 6 cam ... 'D' ... ." .' . ... (1:l:l) are relatively small. Compositions B-4 6-No. 6 caps ... ... ,.. ... F ... , . . (paraffin-rosin-petrolatum, 1:2:1) and B-5 (paraf6-No. 6 caps ... ... ... ... F F ... 4-No. 6 caps ... ... ... ... ... fin rosin-petrolatum 2 : l : l ) were mixed in 20003-No. 6 caps . . . 'J5' ... ... ... .*. .,. ... ... 2-No. 6 caps ... ,.. ... ... ... rather than 1500-gram lots and thus are not en1-No. 6 caps . . . 26 2D 2D ... ... ... tirely comparable t o B-1, B-2, and B-3 because Sample B-No. 2 ammonium nitrate (coarse). C-2B composition was as obtained from manufacturer4.e 98.5% ammonium nitrate, 1% inorganic, 0.1% paraffin, 0.33% rosin. they were slightly coarser ammonium nitrate prodAll mixed 45 rnin&es in 2000-gram lots in ball mill using ceramic balls. Mix C-2B was ucts owing t o less grinding in the 200-gram mixtreated exactly the same as all others in the series, even though no paraffin-rosin-petrolatum was added to it. ings than in the 1600-gram mixings. b F = failure; D = detonation. Series C was made with sample B-No. 2
9" 4"
1102
INDUSTRIAL AND ENGINEERING CHEMISTRY
good lubricating properties, and by this factor tend to desensitize ammonium nitrate (factor 2 ) . The sensitizing effect by factor 1 alone increases u p to zero oxygen balance, but the preponderance of the increase occurs from 0 t o 1% hydrocarbon. This is probably because the sensitization occurs largely a t the interface between Dhe ammonium nitrate and the hydrocarbon. (Zero oxygen balance in ammonium nitrateparaffin mixtures corresponds to about 5.4% paraffin and the explosive reaction is then essentially as follows:
Q E 880 kg.-cal./kg. where Q is the heat of explosion. At lower percentages of paraffin, the oxygen balance is positive and at higher percentages it is negative. ) B y factor 1alone the sensitiveness of ammonium nitrate-hydrocarbon mixtures will increase a t a decreasing rate as the hydrocarbon content is increased from 0 to 5.47& -4bove 5.4% no additional sensitization b y factor 1 will occur. Factor 2 behaves in just the opposite manner for hydrocarbons in ammonium nitrate. At first, the lubricating action of the hydrocarbon is negligible and the desensitizing effect is small, but becomes large with increasing percentages of hydrocarbon in ammonium nitrate. The sensitiveness of ammonium nitrate-hydrocarbon mixtures thus passes through a maximum experimentally a t somewhere between 0.75 and 1.570. AMMONIUM NITRATEHYDROCARBON MIXTURES IN PAPER BAGS
The authors desire t o mention some pertinent previously known facts concerning the use of ammonium nitrate-hydrocarbon mixtures in paper bags with emphasis on the hazards involved, While it is known t h a t even pure ammonium nitrate may be exploded under appropriate conditions (1, 3, 5 , 8, 9, 11, 13, 14), even the most sensitive ammonium nitrate-hydrocarbon mixtures are actually comparatively quite insensitive. This does not necessarily apply, however, to such mixtures used in paper bags. Actually, the minimum primer and propagation sensitivity studied experimentally in this investigation are not increased by the use of ammonium nitrate-hydrocarbon mixture in paper bags; however, the thermal stability of ammonium nitrate and ammonium nitrate-hydrocarbon mixtures, ordinarily quite high,
Vol. 43, No. 5
is lowered phenomenally in the presence of carbonaceous materials. This situation was described by Findlay and Rosebourne ( 4 ) , and was the subject of an extensive investigation by Kistiakowsky and Guinn ( 7 ) . While the “explosion temperature’’ of explosive ammonium nitrate-hydrocarbon mixtures as the authors are aware from experimental determinations, is in the range 270’ t o 350” C., the results of the studies cited show that, in the presence of bagging paper or cellulose, the “explosion temperature” is lowered t o around 150” C., with decomposition taking place a t an appreciable rate as low as 100’ C. Furthermore, the impregnation of paper by ammonium nitrate increases the ease of ignition of the paper because of the intimacy of the oxidationreduction mixture. ACKNOWLEDGMENT
This work was supported by the Texas City Committee of Lawyers representing plaintiffs in the recent litigation in connection with the explosions of “fertilizer grade ammonium nitrate” on the S. S. G r a d Camp and S. S. High Flyer, April 16 and 17, 1947. It is hoped, that the publication of this information, together with similar studies carried out by others in this connection, will be instrumental in our mutual efforts toward the prevention of such catastrophies. LITERATURE CITED
Aufschlauger, R., Chern. Met. Eng., 30, 619 (1924). Cook, R. M., Ibid., 31, 231 (1924). Davis, R. 0.E., U. S. Dept. Agriculture, Circ. 719 (March 1945).
Findlay, A., and Rosebourne, C., J . SOC.Chem. Ind., 41, 38 (1922).
Gawthrop, D. B., A r m g Ordnance, 6, 47 (1925). Jost, ‘A’., “Explosion and Combustion Processes in Gases,” New York, hIoGraw-Hill Book Co., 1936. Kistiakowsky, G . B., and Guinn, V. P., unpublished data. Lorby de Bruyn, S. A,, Rec. trav. chim., 10, 127 (1891). Munroe, C. E., Chem. Met. Eng., 29, 535 (1922). Nuckolls, A. H., Underwriters Laboratory, Inc., BvlZ Reseaich 20 (1940); 39 (1947).
Saunders, H. L., J . Chem. SOC.,121, 698 (1922). Semenoff, N., “Chemical Kinetics and Chain Reaction,” London, Oxford University Press, 1835. Sherrick, J. L., A r m g Ordnance, 4, 329, 294 (1924). Torsuev, W. S., J . Chem. I d . ( M o s c o w ) , 13, 102 (1926). RECEIVED January 3 0 , 1950.
REED V. VAAR1\;ER AND ROBERT L. ICELAUSE Grasselli Chemicals Department, E . I . du Pont de ATemours& Go., Inc., K’ilrnington, Del. ESEARCH workers in the field of wood preservation have long recognized the need for a reliable and easily reproducible laboratory method for the evaluation of new chemicals, new formulations, and new treating procedures. T h e desirability of a generally approved standard test procedure is becoming increasingly acute because of the growing rate a t which potentially effective compounds arc being made available through the rapid advances taking place in all phases of chemistry. It is no longer practical for each investigator t o compare all promising chemicals by personal tests; he must be able to integrate his results with those of others and, to permit this, a readily dupli-
cated standard technique is required. The results of studies in which two laboratory test methods were critically compared are presented here as a contribution which may aid in bringing about greater standardization. The ultimate objective of laboratory preservative tests is t o make possible, after only a few months of study, accurate prediction of the service life of wood treated in a given manner with a new chemical. It is not likely that this objective will be completely realized in the near future. There are many ways in which information obtained in laboratory preservative tests a t their present stage of development may be safely employed.
