January, 1945
INDUSTRIAL AND ENGINEERING CHEMISTRY
tional powers of the constants are given, since they are employed in calculating the properties of mixtures. The constants for ethylene and isobutane are here reported for the first time. They serve to represent the thermodynamic properties of the pure hydrocarbons with the same degree of accuracy as was previously reported for methane, ethane, propane, and n-butane. With the exception of mixtures containing no ethylene, and three other isolate'd points, the deviation of observed from calculated distribution coefficients does not exceed twice the estimated experimental error. The large variation of the distribution coefficient with composition a t f38.05atmospheres is successfully taken into account by the equation. The deviations of the calculated distributi6n coefficients from the observed values are also summarized in Table I. The absolute average deviation of all points, 1.70/0,is of the same order as the corresponding averages found previously (I in) the binary systems methane-propane, methane-wbutane, end ethane$ butane. The absolute average deviations become progressively less at higher temperatures and higher prwures. This may be attributed in part to the greater experimental accuracy to be an-
59
ticipated a t the higher pressures. Moreover, a t the higher temperatures and pressures, one would expect the equation to be more accurate, as the density of the liquid phase is lower and the compositions of the vapor and liquid phases are more nearly equal. It is evident that the equation of state appears to be as satisfactory -for calculating distribution coefficients in ternary mixtures of light hydrocarbons as for binary mixtures. I n addition, its applicability to mixtures containing olefins is also considered as c o n w e d . ACKNOWLEDGMENT
The financial assistance of the Polymerization Process Corporation is gratefully acknowledged. LITERATURE CITED
(1) Benedict, Webb, and Rubin, J. C h a . Phys., 8,334 (1940). (2) IWm* 747 (1942)* (3) McMiUan, Cole, and Ritchie, IND.ENQ.CHEM., ANAL.ED.,8, 106 "1
(1936).
(4)
Olds, Sage, and Lacey, IND.ENQ.CHEM., 34, 1008 (1942).
Organic Material and Ammonium Nitrate in FERTILIZER MIXTURES N
R. 0. E. DAVIS AND JOHN 0 . HARDESTY Division of Soil and Fertiliirer Znvestigations, U. S . Department of Agriculture, Beltrville, M d .
ITRATES are strongly oxidizing substances and, hence, must be handled or stored with caution. Mixtures of nitrates with easily oxidized materials have presented recognized fire hazards in that, after the combustion point is reached, the reactions are accelerated due to the oxygen from the nitrate. The recent increased use of ammonium nitrate as a fertilizer material has emphasized the possibility of such action with explosions or fires occasioned by the use of a munition material (I 6,, 6). Because of the greater danger to life from explosions, this subject has attracted most attention, but the possibilities of ammonium nitrate contributing to fires should not be overlooked if they are to be avoided. Within the last few months reports have been received of fires, of which a t least one seemed to have started from spontaneous combustion in a base containing ammonium nitrate, superphosphate, and peanut hull meal (3). This base had been made and used for mixtures during the entire fertilizer season with good
results. After the season's fertilizer business was finished, one lot of base was made up to carry over to the next season. The first batch of about 75 tons contained old, well-cured superphosphate. The fire started in a similar batch prepared with green superphosphate. The total amount of mixture was about 140 tons, stored in a one-story, frame building with floor and bin partitions of wood, a metal roof, and a sprinkler system. The fire occurred about 2 weeks after the material was stored and during a period of unusually hot weather. The intensity of the fire caused practically all sprinkler heads to operate, and the fire was extinguished with little damage t o the plant. The partitions to the base goods bin were badly burned. The evidence that the fire started in the base is indisputable and points strongly to spontaneous combustion. Preliminary experiments in this laboratory show that spontaneous combustion occurs in this mixture after storage for several weeks a t 30" C.
Mixtures of nitrates and organic materials give rise to oxidation of the combustible material, but the reaction is usually not sufficientiy rapid to result in visible evidence of combustion. Ammonium nitrate shows a tolerance for small quantities of organic materials, but little has been known concerning the action with larger quantities of organics when diluted in mixtures by other fertilizer materials. Reported evidence of a fire suspected of originating in such a mixture has made it imperative to investigate the combustion probabilities. A base mixture containing le00 pounds of superphosphate and 400 pounds of ammonium nitrate with as little as 50 pounds of an or-
ganic meal has been found capable of originating a fire under unusual conditions. Preliminaryexperimentsshow that spontaneous combustion occurs in this mixture after storage for several weeks at 30' C. From tests with a variety of mixtures the conclusion is drawn that the presence or formation of free acid initiates exothermic reactions which between 90' and 110' C. result in Spontaneous combustion. Proper neutralization with ammonia offers safety from fire under severe conditions, even with much larger ratios of organic meal to ammonium nitrate. Coolingor dissipation of heat will avoid reaching the critical temperature.
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
60
IN 3 HOURS AT 100' C. TABLE I. MIXTURESIGNITING
Materials
Sulu;m&osphate
-Pounds N o . 1 No. 2 1400 1400 400
Peanut hull meal Tobacco sterna Lime Ammo-Phos KCI ("4)
200
., .. ..
.. ..
2804
400
of Materials in MixtureaN o . 3 No.4 No. 6 No. 6 1400 1200 1200 1400 400 200
..
200
*.
30
... .
*.
*...
..
400 200
'400
400
..
.. .. .. .. ..
200
..
..
200
....
200
..
No. 7 1200 400
200
100
..
.... 200
AT 100' C. TABLE 11. MIXTURESNOT IGNITING
Materials in Mixt., Lb. No. 9 No. 8 1400 1400
Materials ~&gNp~xphate Am-super.
..
400
400 200
NaNO; Peanut hull meal
200
TABLE 111. EFFECTO F FREEACID ON COMBUSTIBILITY MIXTURESHEATED AT 100" C. Materials
-Pound6 No.,12
... ... 400
BOO
Nine
No. 19 1400 kb0
..
Conihner browned
of Materials in Mixtures-No. 20 No. 22 1372 1372 28 28 400
200 Nbhe
400 200 64
Vigorous combustion
OF
No. 2 1 1400
was used with the superphosphate, ammonium nitrate, and peanut hull meal. All the mixtures ignited within 3 hours. Reducing the ammonium nitrate of the original mixture by half had no effect. As the temperature of the material approaches the ignition point, white fumes arenoticed, becoming morevoluminous rapidly; then suddenly at the ignition point, mixed white and brownish fumes come off rapidly in large volume. I n a few seconds combustion is complete. The pasteboard container is bIackened inside and sometimes outside, but not consumed. Examination after combustion of the ash, which remains as a cake, shows that combustion starts i n the center of the mass. The appearance of the container gives'evidence of the intensity of the reaction. I n some cases where ignition does not take place, the interiors of the containers show numerous yellowish to brown spots, giving evidence of oxidation but insufficient t o cause igniiion. Another similar mixture made of 1400 pounds of ammoniated superphosphate containing 2% ammonia, 400 pounds ammonium nitrate and 200 pounds peanut hull meal did not ignite when heated 3 hours at 100' C. This was also true when ordinary superphosphate was used and sodium nitrate replaced ammonium nitrate (Table 11).
400 200 Vig0;ous combustion
With this information before us we decided to prepare a mixture of the same composition and observe results of heating small amounts at 100" C. Twenty grams of the mixture were lightly packed in the central portion of a 3 / ~ i n c hglass tubewith thematerial plugged a t each end with asbestos. The filled tubes were placed in a n oven a t 100" C., but after 24 to 48 hours no change was observed except a slight browning. A similar test was made with 200 grams rolled up in a small paper bag. It was placed in the oven late in the afternoon, and was found charred and blackened in the morning with the ends of the roll blown out. It was evident that combustion had taken place rather violently with the 200-gram batch after a short heating period; the smaller quantity had not ignited in 48 hours. The mass factor required other experiments t o be performed with the larger quantity, for comparison of mixtures that would or would not ignite under the same conditions. IGNITION TESTS
Tests were made on commercial superphosphate (20%), peanut hull meal, soybean meal, tobacco stems, fish meal, untreated granulated ammonium nitrate, and other materials ordinarily employed in preparing fertilizer mixtures. Two hundred grams of mixed material were placed in a half-pint ice cream paper cup (3.5 inches diameter, 2.25 inches deep) with the snug-fitting top pressed down tightly. This amount of material just filled the cup when slightly compressed. The sample set in a metal pan was placed in a n electric oven heated a t 100" C., t o remain as long as 24 hours. The samples that ignited within that period were t o be considered undesirable mixtures; those that had not ignited probably could be considered ielatively safe. The more readily combustible ones ignited within 3 hours. The first mixture tried, and used as basic mixture thereafter, was found t o ignite at about 100" C. It was a base material, about 7-14-0grade, containing 1400 pounds superphosphate, 400 pounds ammonium nitrate, and 200 pounds peanut hull meal; by volume the ratios were about 4: 1:2 in the same order. This and similar mixtures were prepared and tested (Table I). Changes from the basic mixture included tobacco stems substituted for peanut hull meal and materials added as follows: lime, 30 pounds; Ammo-Phos (11-48-0), 200 pounds; potassium chloride, 200 pounds; ammonium sulfate, 200 pounds. Each
Vol. 37, No. 1
EFFECT OF VARIABLES ON IGNITION
FREEACID. The experiment of Table I1 indicates that ammonia probably reacts with superphosphate to prevent combustion. The combustion reaction, then, may be due to the presence of free acid. T o test this, the mixtures listed in Table I11 were prepared. Table I11 also shows the results from heating. Ammonium nitrate plus peanut hull meal (KO.12) and No. 20 showed no signs of heating. No. 19 did not fire, but brown spots were left inside the container wall. I n No. 22 free acid added to the ammoniated mixture, in the presence of both ammonium nitrate and organic matter, caused it t o fire vigorously. This experiment also shows that the products of ammoniation probably have no effect in preventing ignition with free acid present in such mixture. QUANTITY AND TYPEOF INGREDIENTS. A series of tests was made with varying quantities of different ingredients (Table IV). Peanut hull meal was used in amount as little as 50 pounds in 1850 pounds; soybean meal and tobacco stems were substituted for peanut hull meal. Nos. 26 and 27 are 10-6-4 mixtures with less superphosphate and more organic matter. While all of these mixtures (dry and with 5% moisture) ignited, mixtures 26 and 27 produced less damage to the containers than those with larger quantities of superphosphate and ammonium nitrate. Mixture 14 with half as much ammonium nitrate as the original ignited less vigorously. The vigorous ignition of mixture 24 which had
MIXTURESOF VARIOUSINGREDIENTS IGNITED AT 100" c.
TABLEIV. Materials Superphosphate NIIiNOj
$?2iist% meal Soybean meal Tobacco sterns KC1 Sand
TABLE V.
--Pounds of Ingredients in MixturesNo. 5 No. 24 No. 2 5 No. 26 No. 27 No. 14 000 1400 1400 1400 1400 600 200 400 300 300 400 400 330 330 200 .. .. 200 .. 60 600 ... .. .. 260 600 .. ... .. 200 .. ... .. .. 140 140 .. .. 30 30
..
...
....
MIXTURESWITH OTHERNITROGENCOMPOUNDS NOT IGNITED AT 100" C.
Materials Super hosphate NaN& KNO: Peanut hull meal NHdCl
Ingredients in Mixt.. Lb. No. 4 No. 8 No. 7 1400 1295 1028 400
200
..
665 200
..
505
200
267
IN D U S T R I A L A N D E N G I N E E R IN G C H E M I S T R Y
January, 1945
61
PREVENTION OF IGNITION
TABLEVI. VARYINQ AMOUNTS OF POTASSIUM CHLORIDEAND AMMONIUM SULFATE IN MIXTURES
RZQUIRED AMOUNTOF AMMONIA. Since it is probable that free acid is the initiating Materiala 'No. 14 No. 60 80.8 No. 16 cause for ignition in the combustible mixtures, Su er bosphate 1400 1200 1400 1028 1400 1400 1400 N&h% 200 400 200 400 200 200 200 additions of ammonia in different amounts Peanut hull meal 200 200 200 200 200 200 200 were made to an ignitible mixture. The re&Ncfd a 8 0 4 200 60 100 160 .. 200 200 372 160 100 60 sults from heating such mixtures at 100' C. Reaction8 in 3 br. are shown in Table VI1 as well as in Tables at looo C. Fired N&$idt charring #ring charring container Oharring container contamer 11 and 111. The standard mixture was Same reactions were obtained with dry materials and with 6% moisture, no that moisture 1400 pounds of run-of-pile superphosphate, appear# not to be a factor. 300 pounds of ammonium nitrate, 200 pounds of Peanut hull meal. and sufficient water to bring the content to 9%, after the desired ammonia was added as ammonium hydroxide. Where the amount of ammonia in the ammoniated superphosphate was below 2.5%, the mixtures ignited; at 2.5 t o 5.0% there waa no ignition. The pH determinations indicate a relation t o combustibility of the ammoniated mixtures, both before and after heating. EXPERIMENTS WITH DOLOMITE AND LIME. Several series of tests were carried out with the same mixture, modified by substituting dolomite or lime for ammonia. The results with mixtures containing dolomite show that adding from 50 to 300 pounds makes no difference-they all ignited when heated to 100' C.; similar results were obtained when lime was added at the time of preparing the mixture, 30 t o 80 pounds of CaO per ton as agricultural lime (Table VIII). When lime was added to superphosphate alone one week before the test mixture was prepared, the results were the same (Table IX). I n preparing the latter mixtures four batches of superphosphate were thoroughly mixed with different amounts of agricultural lime to furnish the desired percentage of calcium oxide, and 10% water. The limed, moist superphosphates were kept one week in closed containers in the laboratory at room tefnperature (about 25' C.); 1500 pounds of each batch were then mixed with 300 pounds of am0 monium nitrate and 200 pounds of peanut hull meal. The final Temperature, 'C. mixtures used in the tests contained 9% moisture. Heating a t 100' C. resulted in the spontaneous ignition of each of these mixtures. only 50 pounds of organics indicates that the,presence above a EXPERIMENTS WITH OTHERMATERIALS.Several experiments low limit in the mixture, and not necessarily the amount of orwere performed with mixtures containing additional materials ganic material, determines the intensity of combustion. commonly used aa fertilizers. These experiments are mainly O T H ~NITRATES. R Table V lists two mixtures containing exploratory in nature but are sufficiently suggestive to warrant resodium nitrate and potmsium nitrate instead of ammonium nicording. The following are the significant observations derived tste. Mixture 7 contained ammonium chloride and potassium from them: nitrate equivalent t o the amounts of these salts which would be 1. Experiments with double superphosphate indicate that formed if the following reaction were complete: this material reacts similarly t o ordinary superphosphate in mixtures containing ammonium nitrate and peanut hull meal. KCl ",NO: ---+ KNO: NH&l To revent ignition, about twice as much ammonia is required as t t e amount needed by the same quantity of ordinary superThe resultant mixture, however, is a n equilibrium with all four phosphate. compounds of two salt pairs present (4). 2. Employing urea to furnish part of the nitrogen, a mixture None of the three mixtures ignited, a n indication that with of 1300 pounds of su rphosphate, 400 pounds of ammonium nitrate, 200 ounds of%w and 200 ounds of peanut hull meal sodium or potassium nitrate higher temperatures are required to ignited in I% hours when heated at l b' C cause combustion than with ammonium nitrate. These mixtures 3 . Cal-Nitro was used in two mixtures. One contained 400 were tested both dry and with 5oJ, moisture, with the same repounds of Cal-Nitro and 1400 pounds of supe hosphate; the sults. other, 600 pounds of Cal-Nitro and 1300 p o u n x of superphosphate. I n each case 200 pounds of peanut hull meal were presPOTASSIUM CHLORIDE. AIixtures containing potassium chloent. Heated at 100' C., both mixtures ignited but the comride in different amounts were tested. Potassium chloride variea bustion of the one with 400 pounds Cal-Nitro was less vigorous from 50 pounds t o 372; ammonium sulfate, from 50 pounds than with the larger quantity present. to 200 (Table VI). The ammonium sulfate-potassium ohloride 4. Q-NDust a uick neutralizer from cement flue dust, contains 162 of a c t h e 8aO; the total lime equivalent is 42 t o 44%. combination seems more effective in preventing ignition than Ninety- ve per cent of the dust passed -mesh screen. One either alone. Mixtures containing enough potassium chloride t o mixture consisted of 1350 pounds superphosphate, 400 pounds react with all of the ammonium nitrate present, as in 8 and 18, ammonium nitrate 200 pounds peanut hull meal, and 50 pounds seem t o heat considerably; the organic material is charred but Q-N Dust. the other mixture had the same composition except 100 pounds of Q-N Dust and 1300 pounds of superphosphate. the ignition point is not reached so that they are borderline mixBoth ignited vigorously when heated at 100'. C. tures t o be looked upon with suspicion. Ammonium sulfate 6. A series of similar mxtures containing Cyanamid were plus potassium chloride in proportion of 1 :1 t o 3:1,as in mixtures tested. The standard contained 1400 pounds superphosphate, 15 and 16,seem t o prevent ignition. 400 pounds ammonium nitrate, and 200 pounds peanut hull meal. Pounds of In redienta in Mixtures No. 18 No. 17 No. 16
Limitsd
+
N,$t,";Ed+ fk$td
&:&
+
N&$zd*
62
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
Vol. 3l. No. 1
does 8 mixture of 1400 pounds of superphasphate and 4w pounds of ammonium nitrate. But B mixture of 14w pounds of superphoaphata, 400pounda of ammonium nitrate, and 200 pounds of peanut hull meal does ignite. The fact that ammonia will prevent ignition suggests the presence of seid 88 the initiating agent for the reactions, but sinoe dolomite and lime will not prevent ignition, it is probably not free aoid alone hut the potential acid represented by the hydrogen in monocalcium phosphate (7). There ia also marked difference between the hetion of ammonium nitrste and sodium or p o w sium nitrate. Mixtures containinn either of the laat two do not ignite under the same conditions ex1 2 S when ammonium ignite' Figure 2. Materials in Proportion in Mixture: (1) .Mo i'ormds of AmThe properties of ammonium nitrste are pmbably m o n i u m Nitrate; (2) ZOO Pounds of Peanut Hull Meal; (3) 1400 resoonsihlefor thesediffeerenoes. Becsuseof its MY Pounds of 20% Superphosphate decompositioninto 8mmania and nitrio acid, whioh is rapid at 80" C., free nitric soid hegiins to attack Cyanamid wss bdded in similar mixtures in progreesing amounts organic nistter. Free phosphoric acid also acts on ammonium of 20. 40, 60.80.and 100 onunds. as the ouantity of suxerohosnitrate to set nitric acid free. As a powerful oxididng agent, sbte was reduced by the .=me amounts i i corr&pondi& &der. nitric aoid sating an organic matter releases oxygen to form nitrous he mixture containing no Cyanamid ignited in 3 hours when heated at 100' C. Those containing 20 40, a i d GO pounds of acid, and then in succeesion nitrogen, water, and nitmgentetroxCyanamid ignited after 6 hours, and those with 80 nnd 100 ide, an oven more vigomus oxidizing reagent. Also, pure nitric pounds did not ignite in 21 hours. acid st ita boiling point (8G* C.) deeompes partially into nitmgcn dioxide, oxygen, snd water, according to the equation: The presence of 20 to GO pounds of Cyarmmid definitely retarded the exothermic reaotionr and extended the time for igni4HNOI 4NOs 01 2Ht0 tion to over twice that required when no Cyanamid WBS present. With 80 to 1M) pounds of Cyanamid the reaction was inhibited up to 21 hours and probably prevented entirely. The effect of oyTABLE VII. EFFECTOF AMMONIA ON IGNITION OF MIXTURP~ anamide is equivalent to the addition of ammonia, since CyanAT 100" c. amid heated to 100' C. in the presence of moisture, forms oslcium carbonate and mnmonis. Until the Cyanamid reaches that amount which will produce sufficient,smmonin to neutreliee 2.6 2.8 lblOB-28 0.0 YES monocalcium phosphate, ignition i8 delayed; beyond that it a p 20 0.5 YES 2.8 2.8 1.0 Y* 3.0 2.8 30 pears to he prevented. 3.3 2.9 31 2.0 YW I
-
From the various tests it i8 evident that neutralisstion by ammonia added directly 01 produced by heatins Cyanamid is effective in preventing ignition of otherwise ignitible mixtures; furthermore, evidenoe has not shown any other positive treatment that will prevent ignition of mixturn contsining superphosphete, organic material (such as peanut hull meal), and ammonium nitrate when the Lemperature of the mssg is raised to ahout 100' C. To show definitely that exothermic reactions take plaoe in these mixtures, a heating curve ww constructed by plotting the rise in temperature against time, when B sample is pleced in an oven at 100" C. A mercury thermometer with bulb pleced in the center of the mass WBS observed carefully for changes in rate of heating. Figure 1 shows that the tempersture rises grsduelly in nearly a straight line from 30" to 90" C. in about 80 minutes. At 90" the temperature chmges rapidly (5" per minute) to 130" and then in one minute more to 3W"C. Accelerated reaction 8tsrLa st a little below 90" and, fmm the heat of reactions within the mixture, reaches the ignition temperature at 120" to 130" C.,as shown by the almost instantaneous rise in temperature to over 3 W C. White fumes are observed between 90" and 110" and are soon mixed with brown fumes, an indication of reactions that produce the higher oxides of nitrogen. This c m e is positive proof of internal heating from exothermic reactions, which inevitably result in ignition if conditions prevent the escape of heat 88 rapidly aa it is produced. I t also suggests a method for determining the mixtures that may constitute 8 hazard if the temperature within s mas of material should approach 90"C. A mixture of 400 pounds of ammonium nitrate and 500 pounds of peanut hull meal does not ignite when heated to 100' C., nor
No No
2.5 3.0 4.0
60
32 33 34
SPONTANEOUS IGNITION OF MIXTURES
+ +
3.5 3.5 3.8 3.9
NO NO
6.0
3.0
3.1 3.3
3.B
OB LIMEON IGNITZON 0. TABI,EVIII. EFFEC~OF DOLOMITE MIXTUBESAT 100' C.
DO 10mite vr
Lab. No.'
eo.
Lb./Ton Ignition ERsct of Dolornits Nolle Y* 60 YSa loo YSa 200 YSa
16-108-36 38 37 38 38
.Y
300
-----pH---Before ba.ting 2.6 2.8 2.8 2 .8 3.o
Altar hsatinc 2.8 3.0 3.2 3.4 3.4
Eneft o f ~ i m s BD
so * Same mirtura. ae in Table VI1
Ca
Ye YeS YB
30 40
15-10&-4o 41 42 43
(OHh1 ~ e p h c d .NHI.
2.8
3.o 3.0 3.2
2.9 3.0 3.1 3.3
YSa sroapt that dolomite er lime [added u
T ~ L IX. E EFFECT OF LIMEDQUPEBPHOSPEATE IN MIXTUBES HEATED AT 100' C.
48 47 48 49
so
100 150 200
YSa YSa YSa
Yea
Z.6 2.8
3.1
3.8
2.7 2.8
3.1 3.7
3.0
3.2 3.5 3.9
3.0 3.3
3.6
4.6
1.nuR. 1945
INDUSTRIAL AND ENGINEERING CHEMISTRY
The oxidizing ieaotioas with organic matte? Bet in motion 8 multiplicity ofreaotions involving formation of different nitrogen oxides (1). Espeeislly important is the reversible reaction between nitric oxide snd oxygen to form nitrogen dioxide and tetroxide. 2NO i 0,o 2N0, '-s NxO,
whioh takes place revemibly by heating or cooling, and simultane ously with the reduction of ZNO, to 2NO and the union of liberated O1 with readily oombustible materials. The exothermic reactions mon raise the temperature to the ignition point.
Figure 2 rhows the relative volumes of the materials used in the proportion given for the base mixture. Figura 3 preRenta the results of hesting the base mixture placed in an oven at 1W' C. Combustion was lesa violent when ammonia was 2% of the a m moniated superphosphste and w89 inhibited with 5%. CONCLUSIONS
%me mixturm of ammonium nitrate, orgauio matter, and superphosphate m y ignite spontaneously becauae of the presB ~ C B or liberation of free acid. The reactions leading to ignition of suoh mixtures containing superphosphste, ammonium nitrate, and 0rg-o conditioner can be prevented by treatment of the superphasphate with ammonia. The amount required is sufficient to neutralize the potential free soid of monoedcium phosphate. Premidngsuperphosphstewith lime a week before adding other ingredients dws not prevent spontaneous combustion when the ma%a is heated to 100". The neutralisation with ammonia is very mpid because it is thoroughly distributed either as gas or in solution. It is impossible to obtain the same intimate contact between lime particles and superphosphate particles. The pH of mixtures contsining ammoniated superphosphate i8 eiosely related to their combustibility. I t does not show the -e relation where lime is added, probably beoause the reaction with wpezphmphate h much slower. The pH determination in
63
the slurry produced by adding. the required water, therefore, is not an aoourate crit.eriorr of combustibility in ali mixtures. By determining the rste of hest.ing in the interior of B 2Wgrsm sample of mixture when subjected to 100' C. for s t least 100 minutes, an indication is obtained of the probable ignitibility of the mixture under conditions permitting sceumulntion of heat. The results obtained do not minimize, but rather emphssiee, the importance of using any treatment of material that will retard the evolution of heat or will dissipate it more rapidly than it is produoed. Preliminary liming may be effective with b&eient time for reaction t o take place between the lime and superphosphate.
Treatments to retard the initial rise in temperature of 8 mixture will act to prevent combustion, since the & i d tempersture to produoe exothermic reactions leading to ignition is not reached during the ordinary curing process. The temperature must be near 90' C. before exothermic reactions in the maes initiate spontaneous combustion. This investigation i s to be continued to include a study of the fsetors involved in raising the temperature of 8 mixture to the ignition point, the relation of mas8 of material to 8pontsnwu.6 wmbustion, and employable method8 for reducing or eliminating fire hazards in mixt.ures eontsining ammoniun nitrate snd organic materials. LITEKATUKE CITED (1)
(21 ..
(3) (4)
(6) (6)
(7)
Berthelot. M.. "Explosives and Their Power", tr. snd
om-
danaed by Hake and Mitcnab. PD. 213. 409, London. John Murray, 1882. Davis. R. 0.E.. U. S . Dent. Am.. Soil and Fertilizer 1nvostiz.sti&*, Processed Rept.. fan., G44. Drumright, C. G., private oommunioat.ion,June 28. 1944. Mera. A. R.. eihl., IND. ENO.C H ~ M25, . . 136-8 (1933). Monroe. C. E., Chem.& M e t E w . , 26,53542 (1922). Nuckols. A. H., UnderwiiteisLaba..Bull.ReseardiZO(1940). RM8.W.H.. Am. Fertilizer, 80, 5-8 (1934)
