[Reprinted from Scientific American.]
The explosive of this name was discovered in 1833 by Bracounot, who dissolved paper and starch in concentrated nitric acid, and recovered a powdery white substance, which burned with a flash when brought in contact with flame.
Pelouze, about the same time, observed that starch so treated gained in weight. He also noticed that by dipping cellulose matter in nitric acid of 1.5 sp. gr. it became very inflammable.
In 1846, Schonbein announced the discovery of a new explosive, having four times the power of gunpowder, and as being eminently suited to take its place as a propeller of projectiles and in explosive work generally.
Almost simultaneously, Bottger succeeded in producing what he called explosive cotton. He combined with Schonbein to practically utilize their joint discovery.
Otto succeeded in producing gun-cotton independently of Schonbein and Bottger, working up from Pelouze's published experiments. Otto's product was weaker than Schonbein's, as he only used nitric acid in its preparation, and not mixed nitric and sulphuric acid, which the latter used. The publishing of Otto's experiments and their results led many expert and amateur chemists to investigating in this field.
Knop, Heeren, atid Karmarsch discovered that the best gun-cotton was produced by dipping cellulose in the mixed acids, nitric and sulphuric, a fact which was the secret of Schonbein and Bottger.
Publishing and discussing the various ways of producing guncotton created great excitement in the scientific world of that day. As a humorous scientist put it, "The current literature breathes gun-cotton, and the consumption of nitric acid is colossal."
In the meantime efforts were made in France, Russia, and England to introduce gun-cotton and substitute it for gunpowder. But the processes of manufacture and the impurity of the raw materials used were such that the results were unsatisfactory. Fatal explosions occurred in France and England in 1848. The political revolutions of that time drew further public attention from the subject.
An Austrian officer, Captain Von Lenk, by study and investigation, succeeded in producing gun-cotton which excelled all its predecessors in the regularity of its effect and in its keeping properties. Experiments with it from 1849 to 1853 tended to justify faith in its future, and the Austrian government bought the Schonbein-Bottger patents.
In 1853 the first gun-cotton factory established and worked upon a rational plan was erected at Hirtenberg, near Vienna, under Von Lenk's superintendence. His method of manufacture was kept secret until 1862, when he gave it to the French and English, and patented it in the United States in 1864.
In 1865 the Austrian government abolished the use of gun-cotton in its service because of two fearful explosions of magazines filled with it, the cause of which could not then be determined.
In this year Abel made the discovery which took gun-cotton out of the realm of possibly useful explosives and placed it in that of the safe, practicable, effective and useful ones. This consisted in pulping it, to admit of its proper purification, and in compressing it to increase its explosive effect. Upon the Von Lenk-Abel method all gun-cotton is now produced. Essentially, this method is to dip good and thoroughly cleansed cop or weaver's waste in pure and strong mixed nitric and sulphuric acid—one part by weight of the former and three parts by weight of the latter; to wash, boil, pulp, and liberate the resulting gun-cotton from all free acid; then to mould and compress it into the desired shapes and sizes for use.
For the manufacture of gun-cotton in the factory established at the naval torpedo station and war college (Fort Wolcott) in 1883, the cotton used is cop or weaver's waste, which is received in bales of about 500 pounds each. The bales are opened, and the cotton is picked over and placed in the cotton boiling tubs, about 200 pounds in each tub, to which is added about 250 gallons of water and 35 pounds of caustic soda. The cotton is boiled in this solution for eight hours, then drained over night; it is then boiled for eight hours in clear water, again drained, and then thoroughly washed in a centrifugal wringer or extractor. It is thus freed from oil and other impurities.
It is then spread on the wire netting shelves of a suitably arranged dry room, through which hot air, at about 180° F., is circulated, and is sufficiently dried to be picked.
The cotton as received in the bales is full of knots and rolls, and the boiling adds to them. To prepare it for conversion into guncotton, it is necessary to take them out, that the acid may penetrate easily and quickly through all parts of it. To accomplish this result, the cotton is passed through a picker, a machine common to all cotton factories.
Having been opened out by the picker, it is dried as thoroughly as possible. This is done by placing it in the wire-netting-bottomed drawers of a specially constructed drier, that is closed when filled, through which, and its contents, hot air at about 225° F. is driven by a Sturtevant blower, which draws its air through a steam heater. In this drier it is left for eight hours, at the end of which time it is estimated that not more than I to of one per cent of moisture remains. Water is liberated by the action of nitiic acid upon cotton, and to avoid weakening the former any more than is absolutely necessary, and to prevent dangerous increase of temperature, the latter must be as dry as possible.
When dry the cotton is stowed away in powder tanks, so that it may be conveniently handled, and also kept dry. It is now ready for the conversion process.
This is carried on in the dipping room, which is fitted with cast iron dipping troughs, located in a tank of running water, proper cooling troughs, and acid reservoirs. The acid used is received already mixed, contained in iron drums of about 1200 pounds capacity. The mixture is, as nearly as possible, one part by weight of pure nitric acid of 1.5 specific gravity to three parts by weight of pure sulphuric acid of 1.85 specific gravity, and costs 31 cents a pound. As in the converting and the two succeeding steps of the purification process a great deal of acid fume is liberated, the dipping and two following pieces of apparatus are connected with a fan, to take it up and drive it out. The prepared cotton is brought to the dipping room on the railway running through the factory. The dipper fills the troughs with acid and arranges his tools for use. The helper weighs out a pound of dry cotton, with which he approaches the dipper, and pitching about a third of it into the acid, the latter submerges it with a steel fork, made for the purpose, and so on, until the first trough is charged with the pound of cotton. The other three troughs are similarly charged. When about ten minutes have elapsed, the dipper returns to the first trough, and with the fork gathers the gun-cotton out of the acid and puts it on a grating at its further end, and there squeezes the surplus acid out with a hand-press. By the time this is done, the helper has placed a stone jar, into which the two place the gun-cotton from the first trough. The helper presses it down in the jar, puts a cover over, and sets it in a cooling trough. The dipper replenishes the acid, and the trough is charged with cotton as before, and so on, until the day's dipping, about no pounds, is finished. The jars are left in the cooling troughs overnight, so that their contents may thoroughly digest and there remain no unconverted particles of cotton.
From the cooling troughs, the gun-cotton is taken to a centrifugal wringer, two jars at a time, in which the acid is extracted and caught in a drum. This spent acid is sold to the acid manufacturers for three quarters of a cent a pound. Extracting it is a delicate operation, and great care must be taken that no oil or water finds its way into the wringer, for, if it does, the gun-cotton will be ignited, and, under such circumstances, it is very difficult to draw the line between a fire and an explosion.
The gun-cotton, having been approximately freed from acid, is taken to the immersing tub, in which washing out the free acid is begun. Immersing acid gun-cotton in water is dangerous, and must be carefully and intelligently done. In this tub revolves a paddle-wheel, over which is a hopper, that communicates with the wheel by a slot. The gun-cotton is brought from the wringer in a tray, and placed in the hopper, from which it is fed by separate handfuls, down the slot, upon the revolving wheel, and into the flowing water in the tub. If it is otherwise fed down to the wheel, so much heat is developed in that part at the edge of the water that it may ignite, and burn the contents of the hopper and do other damage.
The gun-cotton is taken out of the immersing tub and thoroughly washed in a centrifugal wringer, and then placed in a gun-cotton boiling tub. These tubs are similar to the cotton-boiling tubs, differing from them in having the steam enter through the top, going to the bottom, then through a coil, and out. The boiling space is insulated from the metal pipes by perforated boxing. Live steam does not come into contact with the gun-cotton, nor does the metal of the steam pipe. In this tub it is boiled in fresh water and Jo pounds of carbonate of soda for eight hours. It is then drained and thoroughly washed in a centrifugal wringer, and boiled again for eight hours in fresh water, and again drained and washed as before.
After the second boiling and washing, it is taken to the pulping machine, which is similar to the machine used in paper mills for pulping paper stock. In this machine, which is suitably filled with water, it circulates between the knives until pulped to about the fineness of corn meal.
From the pulping machine it is drawn off into a poacher, which is a large oval tub provided with a paddle-wheel in the middle of one side, working just clear of a platform with inclined approaches. The pulp and a sufficient quantity of water being in the poacher, its paddle-wheel is made to revolve, which causes both pulp and water to circulate, and the latter to wash the former. After an hour's washing the paddle-wheel is stopped, upon which the gun-cotton settles to the bottom. The soiled wash-water is drawn off by means of a telescopic pipe at one end of the poacher. Fresh water is added, and the cleansing continued until the washing water ceases to become soiled. The gun-cotton is then supposed to be clean and without free acid.
A sample is taken from the bottom of the poacher and submitted to the solubility test, to determine what percentage of soluble guncotton it contains, which must be less than ten per cent. The lower orders of gun-cotton are soluble in a solution of one part alcohol and two parts ether, and by means of this solution the test is made. It is then submitted to the heat test, to determine whether any free acid remains. To make this test, small quantities of the sample, thoroughly dried, are placed in test tubes which are fitted in a hot water bath, carrying a suitable thermometer. The mouths of the test tubes are closed with corks, under which are suspended pieces of iodide starch paper, which has been very carefully prepared. The bath is heated to 1500 Fah., and the gun-cotton must bear this temperature for not less than fifteen minutes without turning the test paper brown.
Having passed the tests, the next step is to prepare it for service use. To every poacher full of it there is added three pounds precipitated chalk, three pounds caustic soda, and three hundred gallons of lime water. So fortified with alkali, it is pumped into what is called the stuff chest, a round tank with a vertical shaft, carrying feathers to keep the pulp agitated and mixed with the water.
The gun-cotton being in the stuff chest is drawn thence and moulded, or pressed into shape for compressing, which is accomplished by means of a hydraulic press arranged for the purpose. Knowing the size of the compressed block desired, it is determined by experiment how much of the pulp is necessary to produce it, increasing or decreasing the length of stroke of the press pistons, then the moulding is proceeded with. The standard gun-cotton block for naval use is 2.9 inches square and 2 inches high, to produce which the moulded block must be 2.8 inches square and 51 inches high, moulding at a pressure of too pounds to the square inch.
From the moulding press the blocks are taken to the final press, which is one of Sellers hydraulic presses with an 18-inch ram. In the receiver of this press the moulded blocks are placed between two perforated steel plates, a traveling block is then hauled over and the pump started, which forces up the ram and the pistons on top of it, which act on the gun-cotton in the receiver. The naval service gun-cotton is compressed at three tons to the square inch, and leaves the press with from 12 to 16 per cent of moisture, which is increased to about 35 per cent before issue to the service. It goes into the service packed in the standard tin exercise torpedoes and tinned sheet iron service torpedoes, which are capable of being made water and air tight, and have the necessary fitments for filling, fuzing, and being attached to spars preparatory to explosion.
The public owes much to the various experimenters with guncotton, but owes most to Von Lenk and Abel. The former determined the facts that the strongest and best gun-cotton is secured from the purest and best raw materials, and that to make it safe, its free acid must be extracted. The latter discovered how to make it safe, and how to increase its explosive effect. He also realized its true sphere of usefulness.
The filaments of cotton in the natural state are hollow, and all the spinning, weaving, and other processes to which it is subjected in the manufacturing and commercial worlds fail to destroy these tubes, as they may be called. Their existence caused the failure of the early gun-cotton makers, because, upon dipping the cotton into acid, it permeated the hollows of the filaments, and no ordinary method of washing served to extract it. With free acid in gun-cotton it is a question of short time for decomposition to begin and explosion to follow.
Abel, by discovering the pulping process, enabled the gun-cotton to be thoroughly purified of free acid; as by pulping the filaments are broken up and the water is able to wash it out. Again, by fortifying the purified pulp with a percentage of alkali to neutralize the nitrous exhalations which all nitrated bodies give off, sooner or later, and then compressing this purified product, he presented to the military world the ideal explosive for its purposes.
It is extensively manufactured in England, by government as well as by private individuals. In Germany, Italy, Austria, and other countries it is manufactured by private parties. It is used by the military services of the whole world, and is constantly growing in favor. The Chinese and Japanese are taking steps to establish their own factories and thus free themselves from the European manufacturers.
The United States Government should to-day have a half million tons of it, contained in torpedo and mine cases, distributed along the Atlantic, Gulf, Pacific, and lake coast, and at central distribution points along that line. It should also have a well drilled and organized naval militia, prepared to lay them out properly and put the life of death into them for those who attack us.
In these days, when the Monroe doctrine is expounded to embrace islands 2000 miles and more from the continent; when interoceanic canals are to be controlled; and when it is the mode to twist the tails of the British and Spanish lions, to pull feathers from the Gallic cock and the eagles of Germany and Austria, it were well that many and rapid steps be taken to enable the country to maintain and prosecute a fight, if one should be developed. From the point of view of one to whom war means promotion, aggressive foreign policy might be very promising, other things being equal. Alas! Other things are not equal; and while this country, in area, wealth, population, and latent defensive and offensive war strength, ranks among the highest of first-class nations, yet in its immediately available defensive and offensive power, upon the sudden declaration of war, it ranks little, if any, higher than Denmark. Modern guns, forts, ships, torpedoes, mines, and gun-cotton must be accumulated, and the fighting strength of the nation trained in their use.
Wet compressed gun-cotton is the safest high explosive yet produced. It can be readily and safely transported by any conveyance whatever. It is eminently convenient and safe to handle, store, and work with. It can be sawed, turned, cut, and bored easily and with perfect safety; and the turnings, cuttings, and borings may be worked over, as may old, distorted, or obsolete shapes. It can be compressed in any shapes or sizes.
Dry compressed gun-cotton is safer in every way than gunpowder, and a very small percentage of the whole weight of any charge for explosive work need be dry.
In view of the daily accidents with the ordinary market high explosives, it is pertinent to ask what would happen if the work of lining our whole coast with mines and torpedoes charged therewith were attempted? Our defense would be as dangerous to ourselves as to our enemy. No man fights well who is afraid of his weapon.
The time has arrived for private enterprise to take hold of guncotton. The processes and machinery for its manufacture can be greatly simplified and improved, and its sphere of usefulness much increased. It is certain that the overweening common sense of our naval and military ordnance authorities will, in the near future, cause it to be adopted as the normal high explosive for Government use. Even now, reasonable inducement might be received for private parties to move in the matter.
As superintendent of the factory whose processes this paper describes, I have, in the past three years, made many tons of it, handling it under various circumstances, in both the wet and dry states, without injury to person or property.