Stabilization of Cellulose Nitrate with Ammonia RICHARD E. REEVES AND JOEL E. GIDDENS' Southern Regional Research Laboratory, United States Depurtment of Agriculture, New Orleuizs, La.
T
During the course of experiments on cellul&e nitrate The results are expressed 11) HE authors have obrhes (reciprocal poises). served that it is possible undertaken as a part of the research program of the Cotton linters were purified to cause a marked stabilizaSouthern Regional Research Laboratory, an interesting bs a commercial firm to meet tion of cellulose nitrate by and apparently novel observation was made regarding specificatiorls for linters to be nitrate stabilization. The present report consists of a used in the production of simply, treating the unstable general descril,tion of the phenomenon as it applies to pyronitrocellulose by the material with dilute aqueous Xaval Powder Factory (flusolutions c o n t a i n i n g a m explosive-propellant type cellulose nitrate similar to that idity, 12 rhes), monia. It is remarkable that used in the manufacture of smokeless powder. Freshly Aliddling grade cotton fiber prepared cellulose nitrate which has been rinsed free from was cut successively througb a variety of common bases, including metallic hydroxsuperficial acids prior to drying is highly unstable because two cutting machines reducing the length to ides, carbonates, and alkyl of difficultly removable acids trapped within the fiber. approximately o.15 inch. amines, have failed to produce It is well known that stability improves as these acids are RTas purified to specification such a result. Boiling celluslowly removed by prolonged boiling, beating, and poachby a commercial firm (fluidity, lose nitrate with metallic caring processes. Completely purified cellulose nitrate is a 10 rhes). R700d pulp purified by n bonates is a common practice neutral, relatively stable material which will withstand commercial firm was em(8, P. 263; 9, p. 181, and amelevated temperatures for long periods without undergoing ployed, had a cuprammonium carbonate has also ewp1osiFe decomposition. monium fluidity of 21 rhes. been employed in this manner Nitrate nitrogen analysee (4, p.116). A patent granted mere made by standard techniques using the Du Pont nitrometer ( 1 ) . to Hough, Dufford, and Leonhard ( 5 ) covers a process of boiling using p ' Beating was done in the high 'peed 'Taring cellulose nitrate in a solution kept faintly alkaline by addition of proximately 5 grams of nitrate to 100 ml. of water. ammonium hydroxide. Metallic and ammonium carbonates have The purified cellulases were nitrated in 16- and 32-gra.m lots using 50 parts of nitrating mixture. The cellulose was fluffed by been added in the solid state to cellulose nitrate for the purpose beating small portions in the Karing Blendor for 5 seconds withof absorbing oxides of nitrogen t o suppress the autocatalytic asOut Water. The fluffed ce'lulose Was oven-dried at 100-1050 c - 9 pect of nitrate decomposition (6). Undoubtedly the characteristhen stirred into the nitrating mixture by hand. The nitrating tic ammonia stabilization which is now reported must have mixture was kept a+,approximately 400 C. with occasional stirring occurred in some of these experiments. However, the almost for 20 minutes, after which the nitrate was filtered on a large Buchner funnel, pressed, and quickly dmwned in a large tub of mstantaneous action of cold, dilute ammonium hydroxide sohcold water. The cornpositinn of the nitrating mixture was: and the fact that ammonia differs from other bases in prosulfuric acid, 54.5%; nitric acid, 30%; and water, 15.5%. Thie moting such stabilization, seems to have escaped Prior mention mixture regularly yielded nitrate containing 12.6 * 0.2% nitrogen. in the literature. This paper is concerned with a demonstration Measurements of pH were made with a glass electrode with a Beckman model G PH meter. of the ammonia effect. The mechanism by which stability is proStability tests were made by the widely used 134.5" C. heat test, duced and the quality of the ammonia-induced stability comprise and by a second procedure developed to handle small, unstable the subject of the following paper ( 7 ) . samples with safety and reproducibility. For convenience the latter procedureis called the 110" C. test, although it should not be confused with the S7ielle test which also employs a temperature EXPERIMENTAL METHODS of 110" (4, p. 184). The words "stability" and "stabilization" as well as the term The arrangement of apparatus for the 110' test is illustrated "rinsing," as employed in the present communication, require in Figure 1. The test is carried out by placing 0.5 gram of the celdefinition to avoid ambiguity. Stability refers to the resistance lulose nitrate in a U-tube immersed in a tricresyl phosphate bath displayed by dry cellulose nitrate to spontaneous decomposition kept at 110" * 0.5" C. This U-tube is attached to a smaller (violent or nonviolent) a t elevated temperatures under conditions tube nhich holds 1 nil. of solution containing 0.5% potassium prescribed by the various stability tests, Stability defined in iodate, 1% potassium iodide, and 3 drops of 2% soluble starch this way may not be equivalent to the industrial use of the term solution. Air is drawn through sulfuric acid and soda lime, and vvhich is based on long-period storage at ordinary temperatures. then through the heated U-tube a t the rate of 30 ml. per minute, Stabilization refers to increasing the stability of the fibrous niIn order to sweep volatile decomposition products from the nitrate trate by purification or by other methods, and should not be coninto the iodate solution. The end of the test is indicated when a fused with the stabilization of colloided cellulose nitrate by the blue coloration develops in the second U-tube. The time readdition of chemicals such as diphenylamine. Rinsing means freeing from superficial reagent (acid, ammonia, etc.) by S ~ C ~ S - quired for this to occur is regarded as a measure of the stability of cellulose nitrate. This test allows highly unstable CellUlOse sive changes of water, until the last water squeezed from the nitrate to be evaluated with comparative safety, because the test fibrous nitrate fails to give the usual tests for the particular reis completed as soon as the first trace of acid gas is evolved. The agent. U-tube should be removed from the 110 a C. bathas soon as the blue Cuprammonium fluidity measurements were made a t 25" C. color appears. The 110' test shows excellent reproducibility OD on 0.5% dispersions of cellulose in cuprammollium containing 15 grams of copper and 240 grams of ammonia per liter. British the more unstable samples. Moisture content of the nitrate Fabrics Research Committee type viscometers m r e employed ( 3 ) . not SO critical a factor in this test as it is in those which keep evolved gases in contact TTith the heated sample. Air-dried sample8 Present address, University of Georgia, Athens, Git.
c.
u-
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TABLE I. EFFECTO F
hfMONIA
TREATMENT ON STABILITY
OF
CELLULOSE NITRATE Treatment with "I,
%
Stability, Min.
0.2
134.5' C. test 7 (exploded a t 23 min.) 32,29 30.30
1 0
37,35
None 0.05
l l O o C. test
3.4 80,52,64 40,69, 35 102,100,72,60
TABLE 11. EFFECTOF PERIODS OF
..~MMONIA TREATYEKT AFTER VARIOUS BOILINGWITH WATER I N STABILIZATION OF CELLULOSE KITRATE
Stability, l l O o C. Test, A h . Without Ammoniaammonia treated 18,25 29,18 35,30
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Treatment" Rinsed Boiled 2 hr. Boiled 4 hr. Boiled 14 hr. Boiled 20 hr. Boiled 30 hr. Boiled 40 hr. Boiled 40 hr., beaten Water changed a t end of 4,16, 28, and 40 hours.
25,25
27,31 32,26 23,17
15,23,20
or samples dried in a current of air a t a temperature not exceeding 60" C. were used in the 110" test. The 134.5 'C. heat test was employed essentially as described by Clift and Federhoff ( I ) and others (8, p. 534; 9, p. 66-7). This
test, sometimes called the German test, is widely used in routine control of the stability of cellulose nitrate intended for use in smokeless powder. The test employs 2.5 grams of specially dried nitrate packed into a large glass tube R ith a strip of methyl violet paper supported above the sample. The time noted is the number of minutes required for complete discoloration of the methyl violet paper. The 110 O and 134.5' C. tests often yield approximately the same times of stability for a given sample. In both tests it can be said that times of less than 12 minutes indicate poor stability; from 12 to 20 minutes, moderate stability; and over 20 minutes, good stability. The specifications for cellulose nitrate for use in smokeless powder usually call for a 25-minute 134.5' test, or better. Not well adapted to research work on unstable nitrate, the 134.5' C. test requires many safety precautions not commonly observed in routine control work. During the present work numerous violent explosions occurred, and a bath of sturdy construction had to be employed. The temperature was regulated by the boiling point of a glycerol-water mixture. The bath, placed in a hood behind a heavy safety glass shield, had a string and pulley arrangement for withdrawing the tubes for inspection and for transferring to the cooling receptacle. Tubes containing unstable cellulose nitrate after removal from the bath should be allowed to cool in a heavy metal container kept behind the screen. A 15-inch length of 5-inch iron pipe serves as a suitable receptacle for the hot tubes.
In another experiment cellulose nitrate prepared in the same manner was rinsed free of acid, and part of the material waE boiled with distilled water. Samples of nitrate were removed at intervals during the boiling, and a t the end of 40 hours the remainder was given a 5-minute beating treatment in the Waring Blendor. One half of each boiled sample was rinsed free from acid and dried; the other half was given a 15-minute treatment with 1% aqueous ammonia before being rinsed and dried. The results of the 110 O C. test (Table 11)show that ammonia treatment increased the stability of all samples except the boiled and beaten sample, which had already become stable without the ammonia treatment. A similar experiment showed that cellulose nitrate prepared from wood pulp differs slightly from that prepared from linters or cut cotton, in that it requires approximately 1 hour of boiling before responding well to ammonia treatment COMPARISON O F AMMONIA WITH OTHER BASES. The st?bilizing action of ammonia was tested in comparison with other bases under a variety of conditions. In a typical experiment, nitrate prepared from cotton linters was boiled in water for 1 hour and rinsed before samples were taken for treatment with the various solutions, which, with the exception of the ammonia solutions, contained 1% of reagent dissolved in water. The treatment consisted of allowing the nitrate to stand in contact with 50 parts of solution a t room temperature for 1 hour (unless otherwise noted) n-ith occasional stirring. All samples were then rinsed, dried, and tested for stability, with the results shown in Table 111. In the experiment just reported only ammonia showed anv stabilizing activity. In similar experiments lithium carbonate, pyridine, and urea were without effect. Other bases, notab11 aniline and diphenylamine, are known to produce stabilization of fibrous cellulose nitrate if appreciable amounts are deposited on the fiber. The effect, however, is removable by alcoholic extraction, whereas the ammonia-induced stability is not removed by such extraction. In another experiment (Table IV) ammonium hydroxide was compared to sodium, potassium, and calcium hydroxides. In addition the corresponding acetates in solution adjusted to pH 5 were employed. Nitrate prepared from cut cotton fiber was boiled for 1 hour, rinsed, and divided into approximately 8-gram portions, which were placed in 500-ml. flasks containing 400 ml. of the various solutions. The flasks were allowed to stand at room temperature (25' C. f 2 "), and a t intervals samples were removed, rinsed, and dried for stability tests. The solutions used were ammonium hydroxide, sodium hydroxide, and potassium hydroxide in 0.5% concentration, and 0.16% calcium hydroxide; a faintly acid solution of each of the cations was prepared by neutralizing a portion of each solution and adjusting to pH 5.0 with glacial acetic acid, The data given in Table IV show that stabilization occurred only with ammonium hydroxide and ammonium acetate. Ammonium hydroxide produced maximum stability in 1 minute, ammonium acetate a t pH 5.0 stabilized in 1 day, but the sodium, potassium, and calcium solutions did not produce any measurable stability even in 82 days.
EXPERIMENTAL RESULTS
STABILIZINQ CELLULOSE NITRATEWITH AhfhIONICM HYDROXIDE. In a typical experiment, cellulose nitrate prepared from cut cotton fiber was drowned in cold tap water, rinsed, and boiled for 4 hours under reflux with distilled water. The boiled sample was divided into four parts, one of which was rinsed and dried. The other partswere stirred for 15 minutes with 50 parts of ammonium hydroxide solution containing 0.05, 0.2, and 1.0% ammonia, respectively. The treated samples were rinsed and dried. The resulte of stability testa on the various samples showed that ammonia treatment caused a great increase in stability (Table I). It is apparent that the concentration of ammonia was not critical in this experiment for approximately equal stability was given by 0.05,0.2, and 1.0% solutions.
TABLE 111. EFFECTOF S t abi) tz;
110 Test, hIin. 2,2 2
\
r
BASES ~ ON STABILITY ~ ~ Stability, 1100
c.
Test, Base AIin. Hydroxylamine (stood 3 overnight) Sodium carbonate 2 2 Potassium carbonate 2 1 Ammonium carbonate 40 2 Ammonia 2 1.0% 30 2 0.1% 25 3 0.01% 35 Control (no base used) 2,2 a Crystalline NH,OH.HCl was recrystallized twice from alcohol, and the base was liberated b y adding the calculated amount of NaOH t o the aqueous solution. Base hf ethylamine Methylamine (stood overnight) Ethylamine n-Propylamine Dimethylamine Ethanolamine Triethanolamine Hydroxylamine"
~
~
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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STABILIZIXGCELLULOSENITRATE BY BOILIXQ ON STaBILITY (110' c. TEST) O F SOLUl'IONS COSTAINING Iv. EFFECTS FAISTLYACID SOLUTIONSCONTAINIXG TABLE AMMONIA, SODIUM, POTASSIUM, AND CALCIUM AMMONIUM SALTS. The remarkable activity of . Stability (hlin.) for Treatment of ammonia in stabilizing cellulose nitrate is illusInitial 1 !O 1 5 24 4 7 82 trated in the following series of experiments. BoilReagent pH min. min. hr. hr. hr. days days days ing unstable cellulose nitrate with solutions adjusted ("),OH 11.1 36,32 26.27 30 30 1 8 , 3 0 35 2 6 , 2 0 Dec0mpd.a 5.0 3,3 3,3 3,4 8 2 6 , 3 5 40,45 18,22 60 (NH)rOAc to p H 5.5 containing 1% sodium acetate, potassium NaOH 12.7 ... ,., ... 3,? 2 3 3 Dec0mpd.a 5.0 ... . . . . . . 4 . 0 4 3 5 4 NaOAo citrate, or potassium acid phthalate did not improve KOH 13.6 .... . . .. ,. ,. .. ,. .. 34 , 5, 5 23 2 2 Decompd.' the stability of the nitrate. Parallel experiments in 5.0 4 5 3 KOAc Ca(OH)* 12.4 ,.. 3, 4 4 3 5 Deoompd.' which 0.1% ammonium sulfate had been added to Ca(0Ac)z 5.0 ... 4 , 4 3 4 4 5 each of the buffer solutions showed marked ima These samples had decomposed because of prolonged alkaline treatment and were not subjected t o the stability test. provement in stability. The phthalate buffers containing added ammonium sulfate were also tested a t 0.5 p H intervals between 5.5 and 3.0in the same manTABLEV. EFFECTOF BOILISG CELLULOSESITRATE WITH ner. At p H 4 and below the treatment Kas found to be less effec17ARIOUS ACIDSOLUTIONS WITH AND WITEIOUr .ADDED AmIosIu>i S ~ L T tive than a t p H 4.5 to 5.5. The evperiments reported in Table V employed nitrate prepared from cut cotton fiber. The nitrate Cellulose Nitrate Boiled p H at 2j(, c, Stabillby, 1 Hr. with (SHI)&OI 110 was rinsed free of superficial nitrating acids before being boiled Test, Added, BeginFollowing 1 % Solns., G./100 M I . ning End hlin. Rinsed and Dried for one hour with the buffered solutions. All samples were 3 5.5 5.5 Sodium acetate" rinsed and dried in the usual manner for stability test. 50 5 5 5 4 o'io Sodium acetatea 3 5 5 5 5 EFFECT OF .kM\IONIA GAS. Air-dried, unstable cellulose nitrate Potassium citrateb 40 5.4 0: io 5 5 Potassium citrateb prepared from linters was placed in a stoppered flask in an atmos3 5 4 Porasiium acid phtbalarec 0:io 5.5 35,28 P x a s i u i n arid ph:halarec phere of dry ammonia gas. Samples were removed after 1, 4, 28,36 0.10 5.0 5.0 P x a s s i u m acid phrhalatec 32.35 0 10 4 5 4.5 24, and 48 hours, and exposed to the air to free them from excess Potassium acid phthalatec 21 18 4.0 0 10 4.0 Potassium acid phthalate0 ammonia gas. The 4-hour sample showed slight yellowing; the 3 55 3.5 18 0.10 Potassium acid phthalated 10 3 0 0 10 3 07 Potassium acid phthalated -%-hour sample was dark yellow and obviously degraded. h'one c Adjus:ed w i t h iodisim hydroxide. of the samples showed improved stability in the 110" C. test. 0 Adjusted wirh aretir arid. d .idjus:ed w i t h hydrochloric acid. b Adjusted with ci-ric acid. EFFECTO F ALTERSATINGACID A S D AVIMOSIATREATMENTS. The ammonia-induced stability in cellulose nitrate is not quickly destroyed by dilute mineral acids a t room temperature; but 5 lV TABLE VI. EFFECTSO F ALTERXATISGACID AID AMXONIA sulfuric or hydrochloric acid a t room temperature, and dilute acids TREATMEXT o s STABILITY OF CELLULOSE SITRATE a t the boiling point, reverse the stabilization. I n the following Stability Sample Stability, Sample 1100 c. 1100 c. History History experiment nitrate prepared from cut cotton fiber was rinsed free Test (Consecutive Test, (Consecutive of superficial acids and then alternately ammonia-treated and nfinl Treatments) Min. Treatments) boiled with 0.01 N hydrochloric acid. Samples removed a t the Freshly prepared nitrate 2 Ammonia-treated 23 (same) various stages showed stability following ammonia treatment and 10 30 Acid boil (same) Ammonia-treated ( 1 % NHI a t room temp ) instability folloRing the acid boil. The results are given in Table 3 .immonia-treat~d 21. 21. 28 Arid boil (0 01 N HC!, 2 br.) VI. WITH
... ... ... ...
____ E,!
(same)
DISCUSSION
The preceding experiments demonstrate that aqueous solutions containing ammonia increase the stability of unstable cellulose nitrate. During the course of this work the opportunity was afforded to examine samples of pyrocellulose nitrate taken from the boiling tubs of two factories manufacturing smokeless powder, and to apply the ammonia treatment to a 7200-pound batch of nitrate in the poacher under factory conditions. The results of
'4 6C
U
A
Figure 1. Arrangement of Apparatus for 110' C. Stability Test
tests on the commercial samples paralleled those obtained in the laboratory The 7200-pound batch of nitrate satisfactorily passed the usual stability tests, although it had received less than half the usual stabilizing treatment in the boiling tubs. Cellulose nitrates prepared from linters, cut cotton fiber, or wood pulp all respond to ammonia treatment; the response of the wood pulp nitrate, however, is less marked until it has received a t least a brief preliminary boil. Solutions of ammonia and ammonium salts increase the stability of cellulose nitrate under a wide variety of conditions, whereas, under similar conditions, the metallic hydroxides and salts and the alkyl amines that have been tested have failed to do so. Stabilization with ammonia may be accomplished at room temperature in either alkaline or faintly acid solution, and in the latter a t elevated temperathres as well, without deleterious effects on the color or viscosity of the nitrate. However, alkaline solutions at elevated temperatures are not to be recommended, for at such temperatures decomposition and discoloration occur. It is noteworthy that ammonia gas failed to produce the stabilization of air-dried fibrous nitrate. The ammonia-induced stabilization may be reversed with strong acids; a second application of the treatment, however, regenerates the stability. Demonstration has heen made of the effectiveness of ammo& treatment by means of the 110' C. test and the 134.5 C. heat test. The former measures the time until the first traces of acid g w are evolved from the nitrate a t 110"; the latter, more drastic, measures the interval required for evolution of a very appreciable amount of decomposition products. Although the tests made at
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INDUSTRIAL AND ENGINEERJNG CHEMISTRY
various stages of the stabilization process (Table 11) appear to indicate that the stability produced by ammonia treatment in the early stages of nitrate purification is equal to that obtained on long boiling or by treat,ment during later stages of purification, there are tests that differentiate between the types of stability. A discussion of these other tests and their application to cellulose aitrate stabilized by ammonia is presented in another report (7). SUMMARY
Ammonium hydroxide and faintly acid solutions of animonium salts produce a marked stabilization of unstable propellant-type cellulose nitrate. The corresponding effect is not given by a number of common metallic hydroxides, salts, and amines which have been tested: Kith dilute solutions of ammonium hydroxide the stabilization is produced almost instantaneously at room temperacure. Stability mas measured by tests carried out at 110’ and 134.5 c. The ammonia-induced stability may be reversed by suitable weatment with mineral acids. hut sutwquent treatment with ammonia again produces stability.
Vol. 39, No. 10
Cellulose nitrate which has been stabilized by long boiling and beating treatments is not further stabilized by ammonia treatment. LITERATURE CITED
Clift, G. D., and Federhoff, B. T., “Manual for Explosive L a b e ratories,” 3rd ed., Philadelphia, Lefax, Inc., 1942. Davis, T. L., “Chemistry of Powder and Explosives,” 1‘01. 11. New York, John Riley & Sons, Inc., 1943. Dept. Sei. Ind. Research (Brit.), Fabrics Research Committee, “Viscosity of Cellulose Solutions.” London, H.M. Stationery Office, 1932. Escales, Richard, “Die Schiessbaumwolle,” Leipzig, Veit and co.,1905. Hough, .I.. Duffortl, J . R., and Leonhard, K. C., U. S. Patent 1,785,030 (Dee. 16, 1930). Patrick, m.A., Ibid., 1,596,622 (Xug. 17, 1926). Reeves, R. E., and Ciddena, J. E.. ISD. E m . CHEw., 39, 1306 (1947). Thorpe, J. F., and Wliiteley, 51. A , “Thorpe’s Dictionary of hpplied Chemistry,” 4th ed., I’dL IV, New York, Imngmans. Green & Co., Inc., 1910. V a r Dept. K. S , ) . Trch. Maniial 9-2900 (1940).
Mechanism of Ammonia Stabilization of Cellulose Nitrate RICHARD E. REEVES AND JOEL E. GIDDESS’ Sorbthern Regional Research Znborntory, United States Department of Agriculture, S e w Orleans, La.
T h e first paper of this series (7) demonstrated that anirnonia exerts a specific stabilizing action on unstable rellulose nitrate. The present report examines in greater detail the causes of instability in propellant-explosi! e t! pe nitrate and the mechanism by which ammonia increases atability.
C
ELLULOSE nitrate taken directly from the nitrating bath and rinsed free of superficial acids contains approximately 0.4 to 0.8% sulfate. This sulfuric acid is bound either chemically or physically in some manner which makes it difficult to remove (1, 8, 3,6, 8, 10). Before good stability can be realized with the usual purification process, the sulfate content must be reduced to a low value; but when ammonia treatment is employed on the sulfate-containing material, an entirely different stability relation is observed. Although cold aqueous ammonia does not reduce sulfate content to an appreciable extent, it accomplishes improved stability, apparently by neutralization of the acid. Analyses on thoroughly rinsed, ammonia-treated cellulose uitrates show that a relation exists between the quantities of ammonia and sulfate retained by the fiber. When sulfuric acid is present in the fiber as a half ester, represented by celluloseOSOzOH as suggested by Kullgren (6) one mole of sulfate combines with one mole of ammonia. On the other hand, nhen free sulfuric acid is trapped within the fiber, two moles of ammonia combine with each mole of sulfate. The data in this paper apply to samples of relatively high sulfate content Tyhich have not undergone purification by boiling, and can be regarded as favoring the half ester concept, since the ammonia-sulfate ratio was found to be approximately unity. I n the previous publication of this seriea ( 7 ) an experinlent [{ah reported in which cellulose nitrate was treated with two solutions of approximately equal total ammonia concentration (“3 “I+), one a t pH 5.0 and one at pH 11.2. It was observed that
+
1
Present address, Vniversity of Georgia, kthens, Ga
stabilization proceeded much more rapidly at the higher pH. To investigate this point further, an experiment was set up using buffered solutions of equal total ammonia concentration covering the pH range from 3 to 9. Samples left in contact with the various solutions for 1, 10, 100, 1000, and 15,000 minutes were removed, rinsed, and dried for stability determination. The results show that rate of stabilization increases approximately logarithmically with increasing pH. Calculation of the amount of undissociated ammonia in the various solutions indicates that the undissociated ammonia, and not ammonium ion, produces stability. This observation offers an explanation of some of the phenornena which have been described. The selective permeability of many membranes ton ard undissociated acids and bases has been widely recognized. Jacobs ( 5 )noted that undissociated ammonia is one of the most rapidly penetrating substances, although the diffusion of ions through cell membranes is a slow and complex phenomenon. If the fiber is regarded as a semipermeable mernbrane which allom undissociated ammonia to pass freely but resists the passage of ions, then the failure of ammonium, sodium, potassium, and calcium ions to produce stabilization may be explained. Likewise it becomes unnecessary to assume that sulfuric acid held in the fiber must be bound by primary valence forces, for the trapped acid, being highly dissociated, might not be able to diffuse out for reasons similar to those which prevent the cations from diffusing in. Apparently, undissociated ammonia is able to penetrate the fiber to the vicinity of the trapped acid and effect a neutralizatlon: it is this neutralization which brings about the stabilization and the ammonia-sulfate relation in the treated nitrate. Since the decomposition of cellulose nitrate is autocatalytic (.at least in the presence of air and traces of moisture), the decomposition phenomenon may be explained by assuming that traces of free sulfuric acid are sufficient to set off the autocatalytic reaction. Thus nitrate that is entirely free of acid, or in which the acid has
