The military use of smokeless powder dates from 1886, at which time Vieille introduced into the French service the gelatinized gun-cotton which, with slight variations, constitutes the smokeless Powder of all countries to-day. It is true that England, Italy and Germany, for navy powders, mix nitro-glycerine with the guncotton to form their several powders, but the basis for all of them is gun-cotton dissolved in a suitable solvent (of which there are several), shaped to the desired form in its plastic condition, and then freed from nearly all of the solvent by drying.
The solvent employed for non-nitro-glycerine powders is a mixture of ethyl ether with ethyl alcohol. The process of eliminating the solvent reduces the former to a negligible quantity, while from 2 1/2 to 6 per cent of the latter remains after prolonged drying. This variation in quantity is a function of the least dimension of the finished grain; its further reduction is extremely difficult, and as will be shown further on may not be desirable.
In considering the stability of smokeless powder we thus have to consider, first, the stability of an exceedingly complex organic material, nitro-cellulose; second, this material in the presence of considerable quantities of ethyl alcohol; third, the instability of the alcohol itself as affecting the integrity of the nitro-cellulose.
The question "Can gun-cotton be made stable? " has been asked many times during the past sixty years. Up to the year 1862 the answer had generally been in the negative, but about this time the process of "pulping" or reducing the fibre to short lengths was introduced, and the operation of purifying the nitrated cotton was so much improved by this means as to establish a new status for this hitherto discredited explosive. However, the question did not assume very great interest until Vieille's invention a quarter of a century later raised the whole subject of the stability of gun-cotton to one of immense importance to the civilized world. Prior to that time attempts to use gun-cotton as a propellant in its fibrous state had failed, and, as an explosive, it could not compete in price or utility with many other compounds.
In this paper the writer employs the term gun-cotton indiscriminately for all forms of nitrated cotton fibre, the principal difference between the so-called military gun-cotton and that designated as "pyro-cellulose" and "collodion-cotton" being merely one of solubility, the dividing-line as to nitration not being well marked.
What is a stable powder? We naturally expect all organic substances to be destroyed through the lapse of time, although we have good examples of the survival of cellulose in the form of paper and papyrus for hundreds of years for the former and thousands for the latter. Nitro-cellulose in the form of smokeless powder seems to have an unfavorable history when the extreme care with which it is prepared is considered. Enormous quantities of it are used in the manufacture of celluloid, photographic films and pyroxyline varnish, and we rarely hear of its spontaneous combustion in these forms, notwithstanding the fact that little or no care is used in storing them or supervising their stability, once they are manufactured.
On the other hand, gun-cotton itself furnishes a perplexing history. While it is generally stored in a wet state and thus its spontaneous combustion prevented, much of it exists all over the world that is kept for years perfectly dry with no untoward results. Messrs. Du Pont of Wilmington have a sample of the original gun-cotton made by the inventor, Schonbein of Austria, which has been in their possession since 1850. This was kept in considerable masses in the dry state until 1894, when it was found that its heat-test had become so low that for safety it was stored wet. That unpulped and therefore imperfectly purified gun-cotton has endured for nearly half a century without becoming alarmingly unstable is a fact that emphasizes our ignorance of the whole subject. Nor is this ignorance the result of lack of study; the greatest laboratories and the most skillful chemists of the world have been devoted to its investigation for years.
Judging from the 25 years' history of smokeless powder, it must be admitted that in the present state of our knowledge of its manufacture, perfectly stable powder cannot be produced. With the most exquisite care in conducting every operation we find that one lot will exhibit signs of decomposition in perhaps two years, while another lot, made as we think under precisely similar conditions, will endure for three or four times that period. This fact constitutes the most baffling phase of the problem, and its lesson needs no elucidation.
If, however, we can produce powder that, stored on board ship, under the exigencies of the service, will remain stable for a period long enough not to demand examination at such frequent intervals as to constitute a burden and interfere with general operations, we may be satisfied. That much undoubtedly has been accomplished. In other words, under the present process of manufacture and system of supervision after manufacture, we may feel a reasonable assurance in regard to the powder on board ship. However, allowing for human error and even negligence, it is interesting at this point to consider just what degree of danger attends the spontaneous combustion of one or several charges of powder in a ship's magazine. Fortunately, the comparatively long list of such accidents that have already occurred abroad removes this question from the domain of conjecture into that of practical experience.
French cruiser Vauban in September, Two, while bound from Saigon to Nagasaki, suffered an explosion at 3.10 a. m. A considerable fire resulted and the magazines were flooded. At 3.40 the fire was subdued. A subsequent examination of the magazine showed that one 9.4-inch powder tank had been burst and its contents destroyed.
French cruiser Descartes bound from Taku to Hong Kong. October 25, at 4.20 p. m., an explosion took place in the lower 64-inch magazine. Volumes of thick nitrous smoke with jets of flame rose through the ammunition hoist, at the same time large volumes of gas and flames made their way into the upper magazine through the communicating hatch, which was open. Fifty minutes before this the temperature was taken and found to be 83° F. Moderate sea. Refrigerating apparatus had been running since 8.30 a. m. A subsequent examination showed that the powder in 187 cartridges of the upper magazine was in a bad state and it was thrown overboard. In the lower magazine two cartridges. were found empty; the second had its base near to the mouth of the first in the same line. Evidently the firing of the first had exploded the primer of the second. A third lying above the first was found to be full of spongy carbonaceous material.
French cruiser Forbin. At 2.30 a. m., April 15, 1905, an explosion quickly followed by a second was heard in the after part of the ship. A column of flame and smoke poured out of the openings of the 5.5-inch ammunition hoists slightly burning four men about the hands and face. The resulting fire was quickly mastered and the after magazine flooded. A few minutes later the smoke had thinned sufficiently to permit an examination of the magazine. It was found that the door had been blown open and the magazine light blown from its frame; the bulkhead opened at a seam. All of the planking and woodwork in the magazine had been burned or shattered and considerable other construction material damaged. Two cartridges had exploded; four were found to be expanded; two shell charges of black powder exploded; five shell separated from the cartridge cases and seventeen other cases damaged.
The Chanlemagne had an explosion on December 30, 1904, in the 4-inch magazine. Two men who were in it at the time, though injured, escaped and made their way to the sick-bay. The gunnery officers proceeded to the magazine and found it full of smoke through which flames were visible. The door was closed and the magazine flooded. Out of a lot of nine cartridges that had been lying together, two cases had separated from their projectiles and were found lying on the floor, one of them torn into several fragments and the other flattened. Parts of the woodwork had caught fire.
On the French battleship Jena: On March 2, 1907, while lying in dry-dock at Toulon, flames shot up at 1.30 p. m. just forward of the after 12-inch turret. About 12 or 15 seconds afterward two explosions took place, the second following the first almost immediately and described as a "tonnante." The second explosion threw wreckage and debris into the air and inaugurated a series of half a dozen explosions that lasted an hour. The after part of the ship was practically destroyed and a large number of men lost their lives. In this case a black powder magazine adjoined that containing the smokeless, and at the time of the explosion the cover to the opening between them was open.
The British cruiser Fox and battleship Revenge are reported to have found one or more cases in the magazines with their cordite contents burned, the remainder of the contents of the magazines unharmed.
Instances similar to the above can be cited to the number of twenty-five or thirty, including magazines on shore. They all go to show that where smokeless powder is kept separate from black powder, the danger and destruction that will result from a fire in the former are small. The writer has witnessed two magazine fires on shore; one in a brick building containing 9,000 lbs. of black powder, the other in a frame dry-house containing 70,000 lbs. of smokeless. The detonation accompanying the former was indescribable and the destructive effect very great. In the latter case the noise was muffled and low; the building was leveled to the ground, but its materials were not dispersed; whereas the black-powder magazine disappeared entirely.
The very recent case in which the contents of a powder-tank took fire in New York Harbor will be readily recalled. It will be remembered that this tank was part of the cargo of a powder lighter containing many similar tanks and that, although the woodwork of the vessel caught fire, a considerable time elapsed before other powder was burned.
In dwelling on these mishaps the writer has had in view the endeavor to give a clear view of the extent of the danger accompanying the decomposition of powder. If the black powder is stored in separate magazines, it is evident that the chance of ships being destroyed is very remote. That the danger is remote should in no way cause us to relax our vigilance and care with respect to the whole subject; on the other hand, it is well to understand just what the chance is in order that we may not be hysterically misled into costly and cumbersome devices to protect the magazines. Since a large number of these mishaps have occurred in the French navy, it should be noted that their powder is similar in composition to all other gun-cotton powders; these powders only differ materially in methods of manufacture and care in subsequent supervision. Two of the examples are taken from the experience of the English. They employ nitro-glycerine gun-cotton colloids, but these in turn have essentially the same temperature of ignition that ordinary gun-cotton powders have.
Nitro-cellulose powders decompose in four ways. First, when ignited in the open air they burn with a clear pinkish yellow flame requiring several seconds for the combustion. Second, when ignited in a gun the time of combustion is hastened by the pressure and the products of combustion differ from those obtained in the open. Third, when ignited in a partially air-tight receptacle, the powder decomposes in a few seconds, giving off large volumes of thick, yellow, acrid smoke, consisting principally of N204. Lastly, the decomposition that concerns us most—the slow disintegration of the powder that extends through months and even years.
It is outside of the scope of this paper to consider any other than the last mentioned decomposition. As a matter of interest, however, it should be stated that where a more extended conflagration has taken place as in the magazines of the French ships above cited, the third decomposition has to large extent followed the last, and besides the clear burning, volumes of N204 were given off in abundance. This gas is extremely irritating to the lungs and would impede the suppression of a fire by driving every one from its immediate vicinity.
For the first few years following the adoption of smokeless powder in the French navy, it was thought to be a perfectly stable material requiring no more care in its storage or supervision than had been devoted to black powder. This opinion was sustained by Berthelot and Vieille, men of the greatest eminence in the science of chemistry. About 1896, however, regulations for the supervision of powder were promulgated and in 1901 they were made very stringent. Whether these regulations were carried out or not is another matter.
It is to be noted here that there are men whose views cannot be lightly considered who are of the opinion that colloid powders cannot take fire as a result of their slow disintegration, among them Colonel Marsat of the Gavres Commission. This distinguished officer has attempted to demonstrate mathematically his view of the question. The writer, however, has removed any doubts he himself may have had on the subject, by placing a i6-ounce bottle lightly corked, containing a quantity of bad powder, in a place where it was subjected to the heat of the sun (but not its rays). The bottle was inspected every morning for a few days. The stopper was finally found blown out from the mouth of the bottle and its contents burned. A sufficient number of similar cases have come within the writer's immediate experience to place the matter beyond argument.
Before taking up the question of spontaneous combustion through slow disintegration, let us consider the possibility of powder being accidentally ignited through other means.
Friction and percussion have been considered as contributing causes to accidental ignition. So far as the former is concerned, no amount of ordinary handling in bulk will ever generate enough heat to raise powder to the ignition point. The rubbing of the grains together does, nevertheless, generate static electricity, and fires from this cause have occurred, but only, so far as is known, in that stage of manufacture where the surrounding atmosphere was heavily loaded with ether and alcohol fumes. As to percussion, the writer has crushed grains placed on an anvil with blows of a heavy hammer until they were reduced to small fragments, when minute particles would explode occasionally, without igniting the mass.
Powder grains are in the laboratory habitually rasped, scraped with glass, turned in a lathe and otherwise cut into fragments and shavings without ever igniting.
The possibility of exploding smokeless powder by accidental discharges of static electricity has often been advanced.
In 1908 a magazine explosion took place in Batuco, Chile, and the board of investigation found that it was due to spontaneous combustion of smokeless powder; Lieutenant-Colonel Delano ascribed the cause to static electricity. The writer believes that the possibility of accidental fires from this cause is exceedingly small, as he has repeatedly driven electric sparks through thin sheets of powder without igniting it. On the other hand, the electric spark will readily explode a mixture of air and ether fumes, or air and alcohol fumes, if the percentage of fumes to air is sufficiently great. Vieille states that the percentage of ether necessary for combustion is 1.98 and for alcohol 3. Taking into consideration the reluctance with which powder parts with its volatiles toward the final stage of the drying process, together with the fact that all measurements show that the percentages of volatiles in the powder after the lapse of several years remain practically the same as when first packed, it is probable that these percentages are never reached in the atmosphere of the containing vessel and we may therefore dismiss with reasonable assurance the possibility of ignition from this cause.
Returning now to the subject of slow decomposition, powder that has suffered a distinct lowering of its heat test shows no change either in its appearance or ballistics in consequence. When the process of disintegration has progressed further, the grains take on a new appearance, in some cases becoming brittle and to a certain extent friable; in others the surface of the grain assumes a softer gummy texture. The latter grains ignite with great difficulty and burn at an advanced stage with no greater facility than does sugar. The brittle grains burn quite readily, but not at all with the readiness of good powder, and leave a skeleton of ash of about the consistency of cigar ash. It must be noted, however, that when powder has reached either of these conditions, it is far gone in decomposition and must have long since passed the danger point. In fact, it is highly probable the danger of spontaneous combustion was escaped at some point where the powder still had a fairly good appearance.
Among the gaseous products of decomposition are the lower oxides of nitrogen and their evolution is accompanied by heat which, if not conducted away rapidly enough, may raise the temperature of the powder to the ignition point. There is no doubt that the rate of decomposition is a function of the temperature to which the powder is subjected, and high temperatures thus react badly in two ways; first, they hasten decomposition, and second, they impede the dissipation of the heat engendered by that decomposition. Furthermore, warm powder is much more inflammable than cold powder under any circumstances. So we have three very good reasons why powder should be kept as cool as possible. How cool it must be kept practically to avoid decomposition is an interesting and important question. The writer believes that smokeless powder will decompose at any temperature, although as good an authority as Mr. Francis Du Pont is of the opinion that at temperatures below 87° F. the powder of to-day is stable.
The difficulty of proving experimentally any proposition with respect to the stability of powder lies in the great length of time necessary to complete the experiments. It may take months, but probably several years will be required to demonstrate them. However, an inquiry ,on the subject of keeping qualities under different temperatures made in France some years ago seemed to indicate, for their powder at least, that stowage temperatures ranging all the way from 104° F. down to 59° F. had given bad results. The powder had been stored in hot sheds and in cool underground magazines, but after a time it was all found to be in a bad state. Of course, heat is not the only factor working against the integrity of the powder. The presence of moisture seems generally to be admitted to have a bad influence. Contamination with chlorine lowers the stability; hence the necessity of avoiding accidentally wetting it with sea water. The sun's rays have an actinic effect on gun-cotton, and alkalis break it down. Above all are the mysterious impurities that seem to have baffled all attempts at detection. How searching has been the investigation may be shown by the fact that causes for instability have been sought in the quality of the fibre; the region in which it was grown; the amount of twist that had been given it in spinning; the ripeness of the cotton; the amount of acids used in nitrating, and so on. This not only illustrates the extent of the inquiry, but also how remote lie the causes tending to the breaking down of gun-cotton.
It has been stated by Mr. Maurice Jaque that the instability becomes more marked as the extreme limits of nitration are approached. This can hardly be true, since cordite is made up of gun-cotton of high nitration and cordite certainly exhibits no inferiority in keeping qualities to other well made powders.
It is constantly demonstrated in the laboratory that the rate of decomposition is an increasing function of the temperature; but these demonstrations are only made with much higher temperatures than those to which the powder is subjected in storage.
M. Sapojnikoff has made careful experiments in decomposition by heating gun-cotton of three different degrees of nitration, each at temperatures of from 120° to 160° C. and measuring the volume of gases given off at each temperature. A time and volume curve was then plotted from which it is found that while the curves are generally similar for a given powder, they are too erratic in form to permit of any one equation being deduced to represent the whole process. The curves must be divided into at least three portions. After maintaining a fairly uniform rate, decomposition slows rather abruptly and the evolution ceases finally.
It is probable that the danger zone exists during the period of high and regular evolution. I have taken points from his curves of gun-cotton of 12.78 per cent nitration where the amount
{graph}
of gas has reached 50 cc. at all the temperatures. For this particular set of observations it is at this point that the rate begins to reach a maximum and from these data we are enabled to plot a new curve between temperature and time. In drawing conclusions from this curve we are again confronted by the high temperatures necessarily employed, but if the curve holds good for temperatures from 248° F. down to, say 80° F., as it does from
248° F. up to 329° F., we would then have a definite law for the time of decomposition of any given powder undergoing a certain temperature.
The " if " introduced here is a big one, and the writer advances the whole proposition with considerable misgiving. Were we enabled to prove it, the test for any one powder would be to ascertain where its rate of decomposition under definite temperatures reached a maximum and became regular in order to predict when the powder would need watching in the future under normal temperatures.
It has always been assumed that to make durable powder, guncotton of good stability must be used, and the latter must pass rigid tests before it is made up into powder. Dehydration with alcohol dissolves out some of the lower nitrates of cellulose and gets rid of these supposedly unstable bodies. Finally we have in the finished powder gun-cotton and alcohol. Considering ballistic values, it is desirable to reduce the alcohol to as low a point as possible, since it not only acts as a deterrent, causing larger charges to be used, but if it is present in such quantities as to be easily reduced in course of time the velocities increase and the pressures become greater. For stability of ballistics it must therefore be reduced at the beginning, but at the sacrifice of chemical stability since the alcohol seems to preserve the powder by combining with the gases evolved in decomposing powder and thus preventing their assisting in the breaking down process. Under favorable circumstances the alcohol decomposes into acetic acid, but this acid does not affect the integrity of gun-cotton. On account of its higher boiling-point, amyl alcohol has in France been added to the solvent as a preservative. Elsewhere, diphenylamine has been incorporated in the powder with the same object in view.
Unstable powder at no stage down to the point where it is very bad indeed, gives any sign from its appearance of being less than normal. Persons unfamiliar with this fact are apt to suspect powder of being bad from certain flaws in appearance due to harmless accidents of manufacture. For instance, where the gun-cotton has been imperfectly dehydrated it gives an opaque, whitish appearance to the grains. Frequently the first evaporation of solvent after pressing is so rapid as to cool the powder here and there sufficiently to precipitate ether and re-dissolve small portions of the grains, giving them the appearance of having been melted. Again, an excess of solvent in the colloid before pressing causes an undue shrinking of the grains, giving them a shrivelled appearance. It sometimes happens that the die through which the powder is pressed is not working properly and some grains are extruded which have a rough surface. It is the practice now to exclude all such imperfect grains, but earlier powders contained many of them, and while they probably did not affect the ballistics unfavorably it has been thought best to cull them out.
We come now to the means used for predicting the probable duration of powder in a safe condition. Many methods have been proposed and several are successfully employed and they are all based on the assumption that a high heat for a short period will furnish a gage of the amount of destruction that will take place under a low heat for a long period. Whether this assumption is true or not is probably debatable as a general proposition, but the fact remains that the so-called " heat-tests " of which it forms the basis, have for many years supplied us with the principal means of insuring against spontaneous combustion. The heat tests are empirical, and each of the several employed can establish its value by time alone; they all, however, seem to furnish some sort of measure by which we can determine the reluctance with which the atoms part with each other under any stimulus of time and
temperature.
Heat tests are divided into two classes—those in which an acid indicator is employed to mark the breaking down, and those which are volumetric in character and measure the rate of evolution of the products of decomposition. A third system, allied to the first mentioned, employs no acid indicator, but marks the visible breaking down of the powder or gun-cotton by inspection.
The well-known KI starch-test has long been used in testing gun-cotton and has been most serviceable. It depends for its action on the liberated nitrous acid attacking the potassium-iodide and freeing iodine which at once changes the color of the starch to a light straw color eventually deepening into blue as the acid fumes continue to react. This test is extremely delicate and an established standard may be changed by thickening the paper used, or changing its texture or altering the arrangement of the simple apparatus that is employed. Moreover, acuity of vision exercises an influence, and no two observers will note the first appearance of " color " at exactly the same time. It is a test that may be easily nullified by the presence of minute quantities of mercuric chloride; besides, other substances interfere with its proper working. Its very delicacy, however, is its best point, since it permits us to conduct a test in less than an hour at a temperature of 150° F., which is near enough to storage temperature to furnish some idea of what will take place under service conditions. This much cannot be said of any other of the well-known tests. In them we must take for granted the proposition that the behavior of powder
at temperatures above the boiling-point of water will provide us means of predicting its action at ordinary atmospheric temperatures. It is a good test for gun-cotton and can be used in testing powder by subdividing the grains in order to increase the exposed surface, as well as to facilitate the evaporation of solvent so that the latter element will not stultify the test.
In the Vieille test the powder is subjected to a temperature of 110° C. (or 230° F.) in a suitably arranged bath. Litmus paper indicates the evolution of acid fumes and when it has turned thoroughly red the test is stopped for the day, the number of hours it has taken to accomplish this result being recorded. Next day the process is repeated and the hours again recorded. The time of heating required grows less daily until finally the test is concluded when the litmus turns red in less than one hour. The sum of all of the hours recorded is then taken as a measure of the number of months the powder may be relied upon to keep in good condition.
While the Vieille test requires considerable time and attention, It has the advantage of not requiring the operator to conduct it except during the ordinary day's work. It is entirely empirical and took years to establish. Mr. Patterson, chief chemist at Indian Head, finds that it gives good parallel results with the KI starch-test and the surveillance test (to be described next), both of which are conducted at 150° F. This, to the writer's mind, is of great importance as tending to establish the validity of the whole system of testing powder by subjecting it to high temperatures.
The surveillance test is one suggested and developed by Patterson. The powder in this test is enclosed in a bottle fitted with a ground glass stopper and placed in a room kept habitually at 150° F. The first appearance of the red fumes of oxides of nitrogen marks the end of the test. The great advantage of this test is that it dispenses with all indicators, while the test temperature is low enough to be at least in the neighborhood of that of the magazines. It has been pointed rut how the potassium-iodide test may be easily nullified owing to the delicacy of the indicator. In a measure litmus suffers from a similar disadvantage. Litmus paper of an exact standard is not easily obtained. While it takes a comparatively long time to determine the degree of stability of powder by the surveillance test, observations need only be made in the daytime. In the writer's opinion it is the best test of which we have any knowledge.
For the largest-grained powders the surveillance test may require two or three hundred days to complete. This does not mean that we are compelled to wait nearly a year before accepting powder. We know that if it survives this test for a few days we can ship the powder and store it without danger. As the time goes on this assurance multiplies, and finally if it takes 8 or 10 months to break it down, we know that in the lesser temperature of the magazine it will be good for several years. If, however, the surveillance sample decomposes before the normal period, the powder in service which it represents is in no immediate danger, and there will be ample time to withdraw it and take proper action. The whole scheme amounts to this: that every lot of powder afloat has its representative stored at considerably higher temperature under constant daily observation.
The so-called German test is conducted at the high temperature of 135° C. Litmus paper is the indicator, and the time it takes to redden it the measure of stability. It indicates the presence of cellulose sulphates with certainty, but as this impurity is readily gotten rid of in the process of manufacture, a test conducted with a lower temperature seems preferable.
To sum up: Powders are made of very great stability and very moderate stability under apparently the same process. At the outset they appear to be equally good by all known tests, and we have no means of prophesying their future. When, as a result of inherent defects or the vicissitudes of storage, they begin to lower in stability, we have good means of detecting the change and with constant care will be forewarned in time to prevent accidents.