The idea of protecting vessels by means of a very light, self-obturating material was conceived by Admiral Pallu de la Barriere, an officer in the French navy. Being a learned man, as well as an officer of great merit, Pallu de la Barriere devoted a large portion of his life to studying the various methods of protecting those marvelous and formidable floating fortresses which constitute the basis of naval power in every great nation.
In some notes written some years ago the Admiral proclaimed the following, which, in his mind, embodied the main points of naval architecture:
"The battleship, in order to be properly qualified for naval warfare, ought not only to be unsinkable, but she should also preserve during the entire action her stability, her maneuvering power, and the height of her gun-platforms."
He then adds that "the unsinkable quality of ships varies in the merchant- and war-ships.
"A steamer belonging to the Messageries Maritimes was able, after a collision on the ocean, to continue her voyage from Japan to China after her prow had been torn away." This he designated "commercial unsinkability."
"An ironclad, struck by the ram of another battleship, was able, during 1 ¼ hours, to float and reach a point where she intentionally stranded, although her two forward compartments were filled with water."
"This could not be called naval unsinkability. The vessel run into had lost her turning power; the form of her lines had been changed; her rudder was useless, and, therefore, incase of war, the ironclad would have been easy prey."
"The whole future of naval and military construction is contained in this one instance.
"When science has given a correct form to the idea of a vessel, that is to say, a buoyant body filled with a light substance which can be accepted as permanent for all space not used, to enable her to live, to progress and to fight, then it will have produced a battleship which will enter the fray with undisturbed firmness and without fear that the engines of destruction directed against her will be able to affect her in any way, besides being endowed with a species of artificial life sufficient to last throughout her role of destruction."
The realization of this problem (we might say of this dream) Pallu de la Barriere discovered in cellulose, the application of which has now entered into general practice.
There is a story connected with the discovery of the properties of cellulose; like nearly all other great discoveries, it was due to chance. A few years ago the crew of a French man-of-war were engaged in target practice not far from New Caledonia, when, to the general wonder, after each shot it was found impossible to locate the spot where the projectile had struck. They were all certain that the target had been hit, but no sooner did the projectile reach it than it seemed to disappear as if by magic. The commander at the time was the late Pallu de la Barriere, who at once started an investigation which led to the discovery that the shore which had been fired at was not an earthern target, as it was covered with the refuse vegetable matter from a factory where rope was made from cocoanut-fiber, where it had been accumulating for several years. The waves dashing on the shore had massed this fiber and dust into a hillock which the severe storms of the rainy season were unable to wash away.
This strange phenomenon attracted the attention of Captain Pallu de la Barriere, and he came to the conclusion that if such a substance could be applied to vessels of war, the ships protected by it could not sink, as their wounds would close of themselves and so prevent the inflow of water. Besides, this kind of protection would be very economical, as one had but to pick up waste material which was only in the way and of no value to the manufacturer; something that he would gladly offer for nothing to save the cost of removing it himself. He had some tanks constructed which were filled with cellulose taken from that discovered on the beach. He then fired several shots into the cellulose, but the results did not come up to his expectations, as the marvelous effects which were observed when the great mass on the beach was fired at were not reproduced when only a few cubic meters were used.
The experiments were not carried further at this time, but Captain Pallu de la Barriere did not lose his faith in the value of this material, and after extensive experiments carried on by himself, he concluded that the processes employed by the manufacturers of goods from fibers destroyed in a great measure the very qualities which he sought. It was found necessary to sacrifice the fiber almost completely in order to give to the cellulose, by a special process, its maximum effect in small bulk.
I wish to add here that not only the processes, but the application of the cellulose itself to the protection of vessels is covered by letters patent all over the world.
As soon as he had perfected his invention. Captain Pallu de la Barriere laid it before the French Government. His statements were at first received with a general air of incredulity. It was the opinion that he was not in his right mind when he pretended to be able to protect men-of-war by means of this dust so light that a single breath would blow it away, just at a time when experiments had proven that the most formidable ironclads could be penetrated by chrome-steel projectiles.
However, experiments were ordered with the new material. For three years most exhaustive trials were carried on and the results carefully studied. The experiments were kept secret, but the results were so conclusive that the Government issued a decree that cellulose should be used on not only the vessels then under construction, but upon all the old cruisers and battleships.
Since this time, the greater number of the vessels built in France for foreign governments have also been protected by a belt of cellulose. It was in this way that Russia, Holland, Greece, Denmark, Norway, and even Japan have been induced to favor the use of cellulose in their vessels of war.
Hon. B. F. Tracy, the present Secretary of the Navy, wishing to provide the vessels built during his administration with all the improvements which modern science has brought about, desired to have them protected by a belt of cellulose, there being no doubt as to its practical efficiency after the many successful experiments at Norfolk and elsewhere that are reported.
The manufacture of cellulose has now become a domesticated industry, since, in Philadelphia, a company has been organized which has built a factory which will be of sufficient capacity to supply the entire American Navy. The American cellulose will be in every respect identical with the French article, since the company has not only bought the French patents, but has had all the necessary machinery built there in the workshops of the inventor.
For a number of years past there has been an incessant conflict between the gun and the armor-plate. The thickness of the latter has grown while keeping pace with the ever-increasing penetrative power of the projectile. But this conflict must soon come to an end, as we well know that to go much beyond the thickness of armor now carried by the battleships of the world would be to add so greatly to their weights as to make them unwieldy.
When a projectile passes through the enormous thickness of metal which envelopes the vessel, she sinks the more rapidly the heavier the armor.
Endeavors have been made to localize the inrush of water by a system of cellular compartments, but considering the vast energy of the projectiles used now upon naval vessels, their explosion in the compartments would crush in their sides and cause the rivets to fly off by the hundred, letting vast quantities of water into these compartments which are depended upon to afford buoyancy and stability,—also changing the form of the lines, consequently modifying the action of the screw and rudder and so affecting the speed and maneuvering power.
The constructors recognizing this danger, have made many efforts to fill these compartments with some light material of a fixed weight which would keep out the great quantities of water by filling beforehand the large spaces into which the water might flow. They have tried in succession charcoal, sea-wrack, cork, poplar, and Italian brick or light pumice stone, also bamboo from Cochin China, and even tin boxes. In spite of their apparent great lightness, these substances represented in their totality a very considerable weight. And even if they did keep great quantities of water out of the compartments surrounding the shot-hole, they left the shot-hole itself wide open. It was necessary to try to close the hole under fire of the enemy, and after the leak was stopped to pump out the compartments.
An automatic closing of the shot-hole is the only thing that can efficiently protect a vessel during an engagement.
To attempt to close a hole in the side of an iron vessel while she is under fire is most hazardous, and as there are no efficient shot plugs, to attempt such a thing would be almost useless. One must see a leak to obtain a proper idea of the violence with which the water rushes in, blinding the men attempting to stem it, dashing furiously aside every obstacle opposed to dam it, and generally demoralizing the crew. The automatic closing overcomes all these difficulties and dangers, since it acts spontaneously and without the aid of man.
It is true that the latest and most improved types of vessels are supplied with most powerful pumps, but at first the inflow of water might be so considerable that the pumps would not be able to handle it, while the forcing out of the water would lead to the expenditure of an enormous quantity of steam which would reduce the speed and interfere most seriously with the fighting efficiency of the vessel.
In other cases, as when small quantities of water enter into certain parts of the vessel, as, for example, above the slopes of the protective deck, while not sufficient to destroy the buoyancy of the vessel, the mobility of this water affects the stability of the vessel, her period and angle of rolling, and so directly the efficiency of the vessel as a gun-platform. This case is well put in a recent article published in the Naval Institute, which says:
"It is apparent that popular opinion regards the case only as one in which a small loss of buoyancy is the worst result, whereas the danger is likely to be critical, not from loss of buoyancy, but from the effect of the small quantity of water on the stability." Cellulose is not a new substance, as it has been known for years to the botanist and the chemist. It exists in variable proportions in all plants, and in the tissues of certain animals of the lower orders.
The chemical formula representing this substance is C12H10O10.
If you will examine a portion of a small branch of a young tree and subject it to successive washings with cold or hot water, alcohol, ether, weak alkaline solutions or diluted acids, so as to remove all soluble substances, you will have left a fibrous or cellular material which is in effect the skeleton of the plant,—hence the name of cellulose.
The husk of the cocoanut contains a large proportion of cellulose existing in the form of a species of pith which holds together the fibers which surround the nut.
This pith, however, is not chemically pure cellulose, as in its composition there are about 30 per cent of the salts of potassium and sodium (principally chloride of sodium or common salt), traces of manganese, a great deal of tannin and some salts of lead.
The chemical analysis of cellulose made from cocoanut husks is as follows:
Pure cellulose, 83 parts.
Organic extracts, 10 parts.
Ashes, 7 parts.
Total 100 parts.
Far from being detrimental, the presence of these salts and the tannin has the great advantage of rendering the substance safe from decay and the attacks of insects.
The sole enemy of cellulose is the oxidation which takes place when iron and water are in contact with it.
All textile matters are in the same manner subject to destruction under similar conditions.
I wish to insist on this point because I wish you to realize the great importance of its bearing upon the practical use of cellulose. It is most essential that the shipbuilders, who must make use of this substance, shall not lose sight of the fact that cellulose, which contains within itself all the necessary elements for self-preservation, might be damaged by neglecting some simple precaution, such as coating the insides of the cofferdams or steel tanks built to hold it with suitable paint which will prevent the condensation or collection of moisture.
Independent of the above qualities, which are chemical in their nature, cellulose possesses physical characteristics which render it invaluable in shipbuilding, for either vessels of war or of the merchant marine.
It is extremely light, being only one-fourth the weight of cork (the substance usually cited when light substances are spoken of).
On account of its cellular structure it is highly compressible, and in consequence very elastic. Again, it possesses in common with other spongy bodies the property of absorbing water very rapidly by capillarity, and to swell up on account of this absorption.
It is well known that any kind of cellulose subjected to the action of nitric acid, or to a mixture of nitric and sulphuric acid, is transformed into a most inflammable and highly explosive substance, which goes by the name of pyroxyl or gun-cotton, and serves as the base in the manufacture of celluloid. This will explain the confusion which seems to exist very often in the minds of people who are but little familiar with the science of chemistry, between cellulose and celluloid. I have often heard such people express their great amazement that any one should think of lining the sides of ships with such dangerous stuff which might blow them to pieces or cause them to burn like a piece of tinder.
The system of light protection by means of the meal of the cocoanut husk, as conceived by Admiral Pallu de la Barriere, has two distinctly different uses which are often confounded.
First, automatic obturation of shot-holes by a mixture of cellulose and fiber, placed in a loose state in the cofferdams or compartments and then packed. Secondly, to afford an obstruction to the entrance of water into the compartments, by filling them with blocks or briquettes of cellulose.
In the first case the cellulose is employed in the form of a belt of variable thickness, which amounts to 5 or 6 feet in the largest vessels. It exists then in a granulated or pulverized state, mixed with the fiber of the filamentary part of the husk of the cocoanut, in proportions determined by experience as being the best to produce a felt-like mass. The mixture which gives the best results in practice is formed of about 6 per cent of fiber, or more exactly, one part by weight of fiber to fourteen parts of cellulose. This mixture of cellulose and fiber is placed in the cofferdams of the vessels, and there it is compressed to such an extent that it occupies but one-half its original volume.
The effects produced by using this belt, where cellulose and fiber are proportioned according to experience, are, in fact, but the perfection of which wooden plugs furnish the primitive methods. There are in wood two essential parts, one composed of fibrous elements, which adhere to each other and which can produce a sort of felt; the other is composed of round atoms which do not adhere to each other and which are cellulose. We have taken from a fruit, whose nature possessed extraordinary qualities of lightness and imputrescibility, two essential parts—the fibrous portion, and a sort of amorphous cellulose—and have mixed them in a proportion to accelerate obturation and to maintain it.
When a projectile goes through a cofferdam filled with compressed cellulose, the elasticity and absorbing qualities of the substance come into play, for the material contains in itself two forces which manifest and defend themselves while under the influence of the two causes of destruction, the projectile and the water, acting successively at short intervals on the buoyant body.
1. By the force of the projectile, the elasticity of the material (filaments and granules) naturally causes same to give way, making a passage, and then a reaction takes place by which the material assumes its original form, remaining constantly in contact with the projectile until it leaves the cofferdam, and avoiding any kind of a punching effect. The form of each particle of cellulose and its mobility in permitting the granules to slip over each other facilitate this instantaneous obturation, and the disposition of the fibers retains the cellulose in place. The material is not scattered because it gives way, and takes its original place because it is elastic. The density of the penetrated layers is not sensibly disturbed.
2. When the water coming in contact with the material attempts to follow the projectile on its way through the hole, the material develops still another important quality which, up to the present, had been latent. The swelling of each of these particles coming into contact with the water produces a very lively burrowing, the water now being the most active agent to prevent the water itself from passing through. Thus the projectile provokes the obturation and the water makes the wall solid.
Man does not interfere in any way by any supplementary compression, and the obturation may be said to be entirely automatic.
The cofferdam being of limited dimensions, the weight of the water absorbed may be neglected and cannot influence to any degree the speed of the vessel.
If the projectile happens to explode within the limits of the cofferdams, the greater number of the pieces of the shell will be embedded in the mass of cellulose, preventing in this way loss of life and the destruction which the pieces would cause in the structure of the ship. Hence we have here a substance which is not only obturating but ensures also the intactness of the bulkheads enclosing it. While the obturating value of cellulose is not questioned, many people have said that it would be blown out of the cofferdams by the explosion of shells within them. The statements I have made are, however, based upon actual experiments with 6-inch shells.
The other use of cellulose in the form of water-excluding briquettes which completes the system of light protection I shall now speak of. This is intended to answer quite a different purpose. Where it is used the question of stopping holes need not be considered, but as I have stated before, it is a case of occupying in advance large spaces not utilized in the vessel which would become dangerous when filled with water. It is necessary to fill such empty spaces with a substance which possesses certain essential qualities. It must be very light so as not to add unnecessarily to the weight and so reduce the amount which can be carried in powder, shell, etc. It must be perfectly waterproof, so that it will not absorb water and constantly increase in weight. It must be secure against the various causes of destruction which might in time render it useless, such as insects or rot.
In this case, the qualities of absorption, of obturation, and of elasticity are not aimed at, but it is still to cellulose that we must turn, not in the loose and compressed state, but in the form of briquettes enveloped in a waterproof covering, because of all substances known it is the lightest which can be used for this purpose, and it is not subject to decay or the ravages of insects.
As an example of the comparative lightness of cork and cellulose I wish to cite the following:
The English battleship Inflexible has her cofferdams filled with 143 tons of cork and oakum; viz. 68 tons of cork of a density of 0.24, 75 tons of oakum of a density of 1.00.
If we should fill the same spaces with cellulose of a density of 0.12, the total weight would only be 43 tons, saving 100 tons out of 143 and at the same time securing much better protection.
If, then, we consider that briquettes of cellulose weigh about 8 pounds per cubic foot, while sea-water weighs 64 pounds, we can easily understand the importance of opposing the entrance of water by filling in advance the spaces with a substance eight times lighter than the water which would otherwise fill them.
Coal is often relied upon as a protection against gun-fire, but the extent to which it can be depended upon has led to many discussions among naval constructors, some of whom contend that it is to be depended upon as a protection: on the other hand, if it is to be used in the furnaces of the boilers, we are again confronted by the empty bunker open to the inflow of water.
I do not wish to enter into a discussion as to the merits of coal protection, but it strikes me that even admitting that the bunkers are full up to the moment of going into action and offer in this condition efficient protection, this protection is obtained at a great cost as to weight, since coal is more than eleven times heavier than briquettes of cellulose.
Cellulose has been proved efficient during a number of years, and it is well established both by experience and practice that the vessel protected by it will continue to float, that is to live, even after being struck many times, and that she will preserve during an action her stability, her maneuvering power and the horizontality and height of her gun-platform, that is to say, her metacentric height.
Numerous experiments with different-sized projectiles have been made in France and other countries upon cofferdams filled with cellulose.
The detailed official reports of all these experiments would take up too much space in this article. The reader will be able to find them in a volume shortly to be published about cellulose.
I shall simply take as an example one of the recent experiments made in Norway at the Horten Navy Yard during the month of August, 1890, in order to give you an idea of the effect of shot upon cofferdams.
The target used at Horten was identical in form and dimensions with a cofferdam of the gunboat Viking, then under construction. It represented a belt of cellulose 8 feet high, 7 feet 9 inches long and 3 feet 4 inches thick. Three projectiles of 6 inches in diameter, weighing 68 pounds, were fired into the target. Two of these projectiles exploded within the limits of the cofferdam, and you could see a little smoke in each of the holes where the pieces came out. The shell which exploded in the cellulose ignited a small part of the cellulose directly in contact with the flame. A close examination showed that this fire was only on the surface; in spite of a strong breeze there was no flame, and the parts which were ignited could only be distinguished by small charred spots where the flame had passed.
To arrive at a proper understanding of the damage which might be caused by an accident of this nature, the cellulose was permitted to burn for half an hour; it was then easily extinguished with three buckets of water. The quantity of cellulose burned in each of the holes was scarcely two ounces.
I call your attention to this fact because among the many foolish things said about cellulose by those who do not understand its nature or have an interest in decrying it, it has been said that the presence of cellulose on board ship would lead to grave dangers from fire.
The experiments recently made at Norfolk, Va., by the board appointed for that purpose proved that cellulose, even in a loose state and in the open air, burns very slowly and without flame. And, furthermore, one can easily understand that when it is tightly compressed in an air-tight compartment it would burn even more slowly. Again, as a closing argument and one which is most conclusive, it must not be forgotten that the cellulose is placed in the wake of the water-line of the vessel, hence, when a shot is fired into it, the water which follows the shot at the moment of its entrance would extinguish the fire if any could possibly occur. Please pardon this digression. I shall now return to the Norway experiments.
One of the projectiles made an irregular hole in the cofferdam measuring 14 inches by 8 inches, the other shots making holes 11 inches by 10 inches.
While it is not absolutely exact to say that cellulose completely stops the inflow of water, you can see that in actual practice the small amount of water which enters may be neglected. When the projectile has passed through the cofferdam and the cellulose is in contact with the water, it gives rise to a sort of filtering action, which increases progressively for about an hour in the same degree as the absorption increases in the vicinity of the part of the projectile. However, the cellulose swells up in proportion to the amount of water absorbed. The cofferdam being of fixed dimensions, as the mass within it swells it follows that the elements which compose it are more closely pressed against one another, so reducing the passages and arresting the inflow of water in the measure that the cellulose becomes soaked. The leaking through always begins with a single drop, and I have seen cases where this drop did not appear for an hour.
In the Horten experiment the shot-holes were immersed in water to a depth of 4 feet, when the following was noticed:
The first drop of water came through the largest hole in about 6 minutes, through the second hole in about 19 minutes, and through the third hole, in the case where the shell had not exploded, in about 38 minutes.
At the end of 30 minutes there flowed through the three holes 22 gallons per minute, and at the end of an hour 34 gallons per minute. In a very little time after, the flow was reduced to 2 gallons per minute for all three holes. It is evident that this small quantity of water could easily be handled by a small hand pump, and that it is insignificant when compared with the torrents which would flow through a hole 14 inches across under a pressure of 4 feet.
As yet no vessel protected by a belt of cellulose has been in actual combat, so that we cannot judge of its action in battle. Recently the Danish government has made a daring experiment which proved its efficiency and at the same time justified the confidence which it had inspired in those who knew it. In May of last year, the last man-of-war built at the Amerger Foelled shipyard at Copenhagen having a belt of cellulose, had a six-inch shot fired through the port bow, the shot coming out on the starboard side. The vessel then steamed about for three hours at a speed of sixteen knots per hour and with the water rising over five feet above the shot-holes. The cellulose proved so effective that at the end of the three hours less than fifty gallons of water were collected in the ship. (See figure.) At about the same time, during the French maneuvers, the cruiser Surcouf was run into by a torpedo-boat which made a hole 12 inches in diameter in her bow. The boat sank, but the cruiser, thanks to the cellulose, only took aboard an insignificant quantity of water.
A few weeks later, this same cruiser Surcouf, which formed part of the French squadron when visiting the Scandinavian ports, was run into by the British boat Cormoran during a heavy fog. For the second time upon the same vessel the cellulose filled its role of protector, while the English vessel would have sunk beyond doubt had not the Surcouf gone to the rescue.
I will now refer to the probable use of cellulose upon vessels of the merchant marine. In the near future the passenger steamers will be obliged to follow the path already pointed out in the man-of-war.
It is certain that the system of subdivision into a great number of compartments, which has been in use for several years in the building of large passenger steamers, is the first step towards greater security, but we have actual examples where the enormous vessels have been sunk in spite of their water-tight compartments.
It is evident in certain cases where bulkheads are broken in and adjacent compartments thrown into communication, where the water pours into the vessel, extinguishing the fires, stopping the engines and causing terror and madness in the bravest, the water-tight compartment system is not all-sufficient to ensure buoyancy, because the water-tight bulkheads no longer keep out the waves.
If by means of a belt or wall of cellulose a protection can be found against the devastating effects of an explosive projectile passing entirely through the belt, how much stronger may be our faith that this protection will be efficient when in place of such an engine of destruction we have only to withstand the shock of wreckage or rocks, which smash, crush or break, but do not pass entirely through.
There may be laws requiring vessels to provide themselves with night-signals, fog-horns and the most powerful steering arrangements, to reduce their speed and to follow the rules of the road in fog and storm. Whether it conform or not to these rules, the steamer provided with cellulose, in virtue of its consequent unsinkability, will have nothing to fear from the blows that she may receive from reefs forgotten by the chart-makers, from icebergs, or even from a blow from another vessel.
In these times of feverish competition, where ship-owners bend every effort to swell their passenger lists, some calling attention to the excellence of their cuisine, others to the comfort of the vessel or the shortness of the passage, the palm must be given to those who can say: "Upon our vessels, guaranteed against sinking and shipwreck, YOU CANNOT DROWN."
A great nation like the American should take the first step in this much needed development of safety at sea, and I should not be astonished to hear at any moment that one of the great ship-yards of Pennsylvania intended to build a fleet of vessels of this nature, to bring to these shores the hundreds of thousands of visitors who will come to the World's Fair at Chicago in 1893.