For some time past rumors have reached this country concerning the discovery of a new explosive by Nobel which was said to possess even more power than nitro-glycerine while it was at the same time more stable and better adapted to military uses. This explosive was known as explosive gelatine or gum dynamite.
During the past summer I have collected fuller information about this substance which I take pleasure in laying before you. I first learned of it at the Exposition where several manufacturers of nitro-glycerine mixtures exhibited sheets of glue, rolled into cylinders the size of an ordinary cartridge, as representing the character and appearance of the gum dynamite cartridges ; and afterward in a lecture at the Trocerdaro when M. Roux exhibited one of these rolls of glue and stated that the gum dynamite cartridge resembled it. When however I afterward saw a genuine cartridge of the gum dynamite in the laboratory of Prof. Abel at Woolwich, I found that sample to consist of a light amber colored, gelatinous mass which lacked the coherence of sheet glue and rather resembled jelly. This specimen came from the dynamite works at Stevenson, Scotland, but, though they have received intimations from the Government that they will be allowed to manufacture it,, it is not yet an article of commerce, and therefore this may not be the form in which it will appear.
From the specifications filed by H. E. Newton for Nobel in the English Patent Office I have learned the following facts concerning its manufacture.
It has been found by experience that liquid explosives, such as nitroglycerine, methylic nitrate and the like are dangerous to store, transport or use, while solid explosives have been found less dangerous. Hence Nobel has been led to try and devise some plan by which these most powerful explosives could be converted into the solid form. The first step in this direction was the invention of the various forms of dynamite but while by the mixture of the nitro-glycerine with various inert solid absorbents a solid explosive was obtained, this advantage in state was attended with a loss in the power and for some purposes in the efficiency of the explosive. Consequently he has sought for a means for producing the solid form without any loss of power and in the gum dynamite this is attained.
He has found that nitro-glycerine, methylic nitrate and other explosive liquids exert a solvent action on collodion gun cotton similar to that exerted by a mixture of ether and alcohol upon it and that, as the ether and alcohol solution called collodion when concentrated by evaporation leaves the gelatinous film on the photographic plate, so the nitro-glycerine when it has dissolved sufficient of the soluble gun cotton gelatinizes and the solid state is attained.
In some of the explosive liquids, such as methylic nitrate for instance, the soluble cotton readily dissolves at the ordinary temperature but it does not dissolve easily in nitro-glycerine unless it is heated. Therefore he proposes two methods of manufacture. To produce the gum dynamite in the cold he adds to the nitro-glycerine such a solvent for the gun cotton as glycerylic acetic, ethylic acetic or methylic acetic ethers, acetic acid, a mixture of ether and alcohol, acetone, nitro-benzol, dinitro-benzol, methylic nitrate, ethylic nitrate and analogous substances to effect the solution. The quantity of solvent which must be used depends upon the nature of the substance chosen but as a rule about ten ounces of the nitro-glycerine taken to be gelatinized will be found sufficient.
If however the nitro-glycerine be gently heated in a water bath it acquires the property of dissolving collodion cellulose without the addition of the promoting solvent. On account of this property the promoting solvent can be entirely dispensed with or when it is found advantageous to use the promoting solvent we can by heating reduce the quantity used to two per cent, or even less. Since collodion gun cotton is rarely, if ever, homogeneous in composition, its solubility in nitro-glycerine, even when aided by the heat of a water bath, will be found to vary; therefore it needs must be left to the judgment and experience of the manufacturer to add or not a predisposing solvent as above described, and the necessary proportion will be readily ascertained in practice after a little experience.
This process of gelatinization necessitates, (1) that the explosive liquid shall contain no impurity or foreign matter capable of counteracting its power of dissolving nitrated cellulose ; (2) that only such nitrated cellulose or analogous substance is to be used as will readily dissolve in and gelatinize the explosive liquid ; (3) that the solution of the nitrated cellulose (especially if that substance is twisted or compressed) shall be facilitated by mechanical stirring or kneading so as to allow the solvent access to all parts of the gun cotton.
The explosive jelly obtained by this process can be easily pressed into cartridges or any other forms convenient for use. It may be exposed in shallow trays, allowed to harden and then be cut in strips which can be rolled into cartridges. For certain purposes, and especially for military use, it is of importance to be able to dilute or modify the explosive sensitiveness of gelatinized nitro-glycerine to a degree suited to the purpose in view. This is done by adding a quantity of a non-explosive or sluggishly explosive substance possessing the property of dissolving the gelatinizing substance and of mixing with the nitro-glycerine. The solvent substances before mentioned produce this result. They serve not only the purpose of rendering the gelatinized nitro-glycerine less sensitive to concussion, but also reduce the quickness with which it explodes and lower the temperature at which it hardens or congeals by cold. The least volatile substances are to be preferred since they cannot become inoperative through evaporation.
The addition of these substances lowers the percentage of oxygen and raises the percentage of carbon and hydrogen contained in the mixture. To make up for the lost power it is proposed to add to the mixture enough finely divided sodic or potassic nitrate, or potassic chlorate, or other suitable oxidizing material to effect the complete combustion of the excess of carbon and hydrogen in the mixture.
It can be seen that by this means an endless number of such mixtures may be made. Mr. Newton cites four different ones as indicating the different classes of mixtures which may be produced.
I. Nitro-glycerine gelatinized with from four to eight per cent, of gun cotton.
II. No. I with from one half to thirty per cent, of glycerylic acetic ether, or nitro-benzol, or a similar substance mixed with it. The wide range between one-half, and thirty per cent., is given because a very sensitive explosive is required for some purposes, and a very sluggish one for others.
III. Composition II with the addition of an oxidizing agent mixed in sufficient quantity to secure complete combustion.
IV. Composition I and II with the addition of less powerful explosives. These last mixtures, class IV, are adapted to blasting mild rock ; the first class is for blasting hard rock, and the others for military purposes.
Gelatinized nitro-glycerine, when properly confined, may be exploded by means of a common fuse but the explosion is quickened and facilitated by using fulminating detonators. When hardened by cold weather gelatinized nitro-glycerine explodes more readily than frozen dynamite, still it is always a good precaution to head the charge with a primer consisting of a small cartridge of gunpowder, gun cotton, dynamite or uncongealed gelatinized nitro-glycerine.
Gelatinized nitroglycerine to which a considerable portion of glycerylic acetic ether or nitro-benzol or di-nitro-benzol and the like have been added, not only must be fired by a strong detonator but must be confined as in a shell to exert its full power.
Captain Phillip Hess of the Austrian Engineers has made a series of most exhaustive experiments upon gum dynamite to which gum camphor had been added. The gelatine as he used it, contained four per cent, of camphor and ninety-six per cent, of gum dynamite ; the gum dynamite being composed of ninety per cent, nitro-glycerine and ten per cent, soluble nitro-cellulose. This preparation formed a gelatinous, elastic, translucent, pale yellow colored mass (Sp. Gr. 1.6. ) of about the consistency of a very stiff jelly which could be easily indented or cut with a knife, and which did not exude the least trace of nitro-glycerine when strongly compressed, nor show any greasiness. It was submitted to a pressure of 15.4 kilo, per cm3 without separating any nitro-glycerine. Heated up to between 50° and 60° C, it softened but did not become greasy. When ignited, it burned like dynamite or dry compressed gun cotton. When pure gum dynamite was heated slowly, it exploded at 204° C; if heated rapidly, the explosion took place at 240° C. When camphor (4 per cent.) was added, the gum dynamite could be heated to from 300° to 330° C. before it exploded.
According to his experiments gum dynamite containing 4 per cent of camphor is 25 per cent, stronger than kieselguhr dynamite No. 1, weight for weight. If we consider the normal kieselguhr dynamite as having a Sp. Gr. of 1.4., the gum dynamite is by volume forty per cent, the stronger. Compared by weight with compressed gun cotton containing 15 per cent, of water, the gum dynamite is 25 per cent, stronger; if the Sp. Gr. of the cotton be taken at 1.16, the gum dynamite is by volume 75 per cent, stronger.
M. Roux in the lecture referred to, exhibited the following apparatus which he used for determining the relative force of different explosives.
Method of comparing the force of Dynamite No. 1 with Explosive Gelatine by the effect produced by the explosion of equal charges of the two within a block of lead.
The apparatus used is shown in the Fig. It consists of a block of lead C, with a leaden cover D, which is held in place by the heavy weights E E. In the block C there is a chamber A one centimeter in diameter and four centimeters deep. Two grams of the explosive to be tested are placed in this chamber, the remaining space is filled with water, the cover and weights are put on and then the charge is fired by means of the wire F. The force developed is measured by measuring the volume of B after the explosion. Experiment has shown that
The Augmentation of Volume of Chamber
With Dynamite No 1 is 43.55 cm3
With Explosive Gelatine is 61.20 cm3
The Nobel's Explosive Company of Glasgow, report the following results from their experiments with explosive gelatine and other explosives. The tests were made in the Company's mortar with the view of instituting a comparison of the ballistic power of various nitrated com pounds. The charge of explosive employed in each case, was 10 grams, the weight of the shot was 32 pounds, and the distance it was thrown is based upon the average of an equal number of shots fired with the several explosives. The results show that the blasting gelatine is by far the strongest explosive, for practical purposes, known, and that No. 1 and No. 2 dynamite are the cheapest explosives in the market at the present time. The results of the test were as follows.
With Blasting Gelatine the shot was thrown 230.3 links.
Nitro-Glycerine…215
Dynamite No. 1 … 173
Lithofracteur … 151.3
Cotton Gunpowder… 150.7
Dynamite No. 2 … 118
If the ballistic power of blasting gelatine is taken as 100, then in their comparison, weight for weight, the various explosives rank as follows, viz :
Blasting Gelatine 100. Lithofracteur 65.69.
Nitro-Glycerine 93.36. Cotton Gunpowder 65.43.
Dynamite No. 1 75.11. Dynamite No. 2 51.23.
The Societe Generale pour la Fabrication de la Dynamite, Paris, have published a pamphlet upon Dynamite and the Explosive Gum from which I gather the following information.
By the method of manufacture employed an intimate mixture of the nitro-glycerine and the gun cotton is obtained in the form of a gelatinous solid. Thus while this substance still belongs to the family of dynamites since it has nitro-glycerine for its base, it may yet perhaps be considered as an entirely new body and as having but little in common with the numerous compositions which modern science has placed at the disposal of the industries.
This body whose power surpasses slightly that of pure nitro-glycerine, possesses all the characteristic advantages of dynamite. Ignited by contact with a burning body it burns up but does not explode except under the influence of an initial explosion like that which is usually produced by means of a fulminating exploder.
Although a recent invention the explosive gum has already been subjected to trials of its preservative character sufficiently prolonged to show that there need be no doubt as to its stability. Cartridges preserved in contact with the air during more than a year have not shown the slightest trace of alteration. Preserved in water they have not given up the least trace of nitro-glycerine and the substance has not lost any of its force.
The superior power of the explosive gum is due evidently to the elements which enter into its composition ; the hydro-carbons and oxygen are in such proportion that their combustion is more complete than that of pure nitro glycerine.
The explosive gum tested freely in the air appears to ally itself to the slowly detonating dynamites and produces effects somewhat more analogous to those of gun cotton than to those of normal dynamite. By the plate proof made freely in the air the impression made on the plate by cartridges of gum dynamite is not as deep as that produced by a cartridge of the 'same weight of dynamite No. 1. On covering the cartridge with an obstacle, such as a handful of damp earth for example, the explosive gum shows its superiority over dynamite No. 1, although not notably so. But if the charges are partly imprisoned, as in a testing mortar, the gum shows a great superiority to the dynamite. Finally if the charges are closely confined as in the blast hole of a mine with sufficient tamping the explosive gum exhibits all its power and surpasses dynamite by 50 per cent.
This peculiarity will probably lead to the frequent use of resisting receptacles for this new explosive. For certain military purposes, for example, when it is employed in breaking up or overturning an obstacle by simply placing the charge against this obstacle the explosive gum should be put in metallic boxes, a measure which is already adopted in France for the ordinary dynamite and for gun cotton.
Let us examine the influence which the discovery of this new explosive will exercise upon the operations of industry and of war.
In the industries the explosive gum will advantageously displace dynamite in those cases where it is obviously advantageous to employ the most powerful explosive, as, for example, in attacking the fronts of galleries in the granitic schists, and at all times where it is economical to advance rapidly by diminishing the necessary number of blast holes and the labor required for the work. Such is again the case in submarine blasting, where the difficulties in placing the charges, the incidental costs, the employment, so onerous, of divers etc., makes it important to diminish as much as possible the number of blasts, and consequently to have recourse to the most energetic means.
But where the success of the gum dynamite appears above all to be assured is for military purposes for which we can say, that, up to the present time, there has been no wholly suitable explosive. The ordinary dynamites while sufficiently stable for use in the industries, where they can be carefully looked after, do not completely meet the requirements of the army and navy. A substance formed by simply mixing mechanically nitroglycerine and its absorbents cannot be exposed, without a certain apprehension, to the vicissitudes, so variable and sometimes so dangerous, incident to a campaign on land and sea.
These considerations have led to compressed gun cotton being sometimes preferred since it does not present the same inconveniences and has above all the advantage of not freezing; but the doubts which some have always had as to the chemical stability of pyroxylin prevent its being supplied except in the moist state. And here new difficulties arise. How can we be assured of the degree of moistness of all parts of the supply during a long storage ; and how may we procure rapidly and without danger under all circumstances the dry cotton which is necessary for detonating the moist cotton? Finally the relative sensitiveness of the ordinary dynamites and of cotton powder will not permit of their use in charging shells, especially for large marine ordnance.
The imperfections of the explosives intended for military purposes is demonstrated by the indecision which has existed up to the present day, in the different armies and the different countries, as to which was the most suitable substance to adopt for the end proposed. Not content with bringing forward compressed gun cotton and dynamite they have been led to try the picrate mixtures and in default of any single explosive which will answer under all circumstances, each service seeks a substance which can at least meet its needs within a certain limit.
It may appear premature to say to-day that gum dynamite has solved the problem of the true military explosive, however everything leads to this presumption. To have the greatest possible force, together with the smallest volume and with the least weight is the first element of this problem. This is undoubtedly resolved.
The chemical stability cannot be doubted by those who recognize this quality in nitro-glycerine. The experience of more than a dozen years is conclusive. Besides the new material may be preserved in water and need not be taken out until at the moment when it is to be used, and hence it cannot offer any practical difficulty from this point of view. Its mechanical stability follows from its process of manufacture. We are convinced that it can be obtained in a definite state.
The new explosive is gifted with a relative insensibility which is of the greatest importance for military uses. Cartridges of dynamite or of gun cotton exploded in the neighborhood of a charge of gum dynamite, under such conditions that other cartridges of dynamite or of gun cotton would certainly have detonated, produced no effect on it. Hess found that while a kilogram of the gum dynamite containing 4 per cent, of camphor exploded in air within 25 cms. of another kilogram of the same did not affect the second mass, the explosion of a kilogram of ordinary dynamite caused the explosion of a second mass of this dynamite placed 35 cm. from the first.
By mixing camphor with gum dynamite its insensibility may be augmented at will. Whilst dynamite and cotton powder are exploded at great distances by the impact of a ball from a gun the explosive gum, rendered insensitive by this process, resists the impact of a ball from a rifle fired at 25 meters. Experiments have established this decisively.
The power to put into the hands of the combatants, without serious danger to them, a destructive engine of such great power ought to have a considerable influence upon the future of military operations. Should subsequent experiments show, what is highly probable, that we can charge large shells with this new explosive it will lead to the casting aside of the armors of our vessels.
DISCUSSION ON THE PAPER.
Lt. Commander Brown. I would like to ask if any experiments have been made with a view to firing by electricity, and also if experiments have been made with shells loaded with gum dynamite?
Prof. Munroe. I do not know of any experiments having been made with loaded shells, but experiments have been made in firing by electricity. It may be fired in this way by the use of a detonating exploder.
Lt. Soley. I noticed that the test of the eprouvette is in general use for testing the strength of the explosives. This is the same test that was formerly used for testing gunpowder. If these explosives can be used in the eprouvette I should think that their action could be so controlled that they might be used in a gun.
Prof. Munroe. I do not feel fully equal to discussing this question, as it is not within my province yet I will say that I do not think it probable that the nitro glycerine explosives will be used for this purpose. When they detonate the motion of their molecules is so rapidly imparted to the different parts of the chamber that the projectile, as a mass, does not have time to move from its seat before the molecules of which it and the gun are formed have been set in motion and ruptured. Nothing can withstand this effect. For a very clear and interesting exposition of this subject I would refer you to an article by Prof. J. P. Cooke in the Popular Science Monthly on The Air as an Anvil.
Commander Sampson. This subject is a most important one in all its phases, and worthy of attentive study by all officers. The problem of the application of gum dynamite or other chemical agents to ordnance purposes is one whose solution would be of great benefit. One curious fact is worthy of notice and that is that the energy of the gum dynamite is greater than that of the nitro glycerine or the gun cotton of which it is made. How is this explained ?
Prof. Munroe. In my lecture before the Institute on the Conditions which Promote Explosions, I showed that when nitro glycerine exploded oxygen or oxides of nitrogen were found in the products and that when gun cotton was exploded that carbon protoxide was found in the products, thus showing incomplete combustion of the carbon. There are believed to be three different gun cottons corresponding to the three nitro glycerines. The gun cotton containing the three atoms of nitryl (N O2) is the explosive gun cotton. The two lower ones are believed to exist in the collodion cotton, and hence when they are ignited the carbon in them would be still less completely burned than in the ordinary gun cotton. Now it seems to me probable that when we mix a small percentage of this with nitro glycerine that we have even more complete a combustion than we have with pure nitro glycerine and consequently more heat is developed and a large volume of gas obtained. This would give a greater energy. It may be that the gum dynamite is not a simple mixture and that the whole detonates simultaneously. While speaking of this subject I would like to call your attention to the fact that this substance was all but discovered some years ago. At that time Prof. Abel proposed the manufacture of an explosive called glyoxylin which was made by absorbing nitro glycerine with the explosive insoluble gun cotton. Had he but used the soluble gun cotton he would have discovered the gum dynamite.
Commander Mahan. How much stronger is this than gunpowder ?
Prof. Munroe. The experiments cited show it to be about seven per cent, stronger than pure nitro glycerine and nitro glycerine when fired by detonation is over ten times as powerful as the same weight of gunpowder when fired by ignition.
It was moved and adopted that the thanks of the meeting be extended to Prof. Munroe.