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A Short Account of Explosives BY ARTHUR MARSHALL A.C.G.I., F.I.C., F*C«S* Chemical Inspector, Indian Ordnance Department Author of “ Explosives, their History and Manufacture, Properties and Tests" WITH 29 ILLUSTRATIONS. PHILADELPHIA P. BLAKISTON’S SON & CO. io i2 WALNUT STREET *9*7 Printed in Great Britain DEDICATED 55? '"permission D o '7l<>,l&-5ltarsl)al SIK DOUGLAS HAIG, K.T., G.C.B., K.C.I.E., G.C.V.O. <£ommandlng-ln-<£l)lef BRITISH ARMIES IN FRANCE. PREFACE N this little book I have endeavoured to present in a clear and simple I manner the main facts concerning explosives and their properties in the hope that it may be of use to the officers of our now mighty army and also to naval officers and the large numbers of men and women who have to deal with explosives in the manufacture of munitions and other ways. The subject of explosives is such a wide one that it has only been possible to deal with the main facts, and these only briefly, but I hope that those who read through these pages will carry away a clear conception of the different varieties of explosives. The most recent facts have been included so far as the interests of the State permit. A. MARSHALL. N a in i T a l , I n d ia . vii CONTENTS CHAPTER I PAGE INTRODUCTORY............................................................................................. 1 CHAPTER II BLACK POWDER AND SIMILAR M IX T U R E S ............................................. 3 CHAPTER III NITROCELLULOSE .............................................................................................7 CHAPTER IV NITROGLYCERINE AND NITROGLYCERINE EXPLOSIVES . .15 CHAPTER V MILITARY HIGH EXPLOSIVES....................................................................... 22 CHAPTER V I COMMERCIAL HIGH E X P L O S IV E S .............................................................. 38 CHAPTER VII SMOKELESS P O W D E R S ........................................................ 49 CHAPTER VIII FIREWORKS....................................................................................................... 6 1 CHAPTER I X PROPERTIES OF EXPLOSIVES.................................................................. 6 6 CHAPTER X IGNITION AND DETONATION........................................................................78 CHAPTER X I PRECAUTIONS viii CH APTER I INTRODUCTORY A n explosive is a material which is capable of giving off a very large volume of gas very suddenly; at the same time it always evolves a great deal of heat. The gas which is thus suddenly formed tends naturally to expand, and in so doing to overcome the resistance of anything which opposes the expansion. The sharp noise, which is always associated with an explosion, is due to this sudden evolution of gas. Heat is liberated at the same time, and this produces a bright light; it also increases the expansion of the gas. A great many explosives are now known, and they may be divided into classes in various ways according as one considers their composition, their properties or their uses. Some are single substances from the chemical point of view, such as nitroglycerine or fulminate of mercury ; others are mixtures, of which the most familiar example is ordinary gunpowder (black powder). In mixed explosives some or all of the ingredients may be themselves explo­ sive. Some explosives are very violent, detonating at the rate of several miles per second; these are termed high explosives. Others burn compara­ tively slowly and are used to propel a bullet or shell from a fire-arm ; these are the smokeless powders. Black powder occupies a position between these two classes. Some can be exploded directly by the application of a spark or friction; gunpowder, if in a fine state of division, can be ignited -by a spark, fulminate of mercury either by a spark or a blow or friction. Other explosives require a small quantity of an explosive of the last kind to send them off satisfac­ torily ; high explosives are usually detonated by means of a detonator charged with fulminate; smokeless powders also are generally provided with a small igniting charge of a more sensitive explosive. There are various special sorts of explosives used for special purposes. For instance, there are “ safety ” explosives used in coal mines ; these are mostly high explosive mixtures so composed that they do not give a hot flame which will set light to “ fire-damp ” or a mixture of coal dust and air. Fireworks are charged generally with slow burning mixtures resembling gunpowder more or less. vol. hi. 1 i 2 A SHORT ACCOUNT OF EXPLOSIVES Of the various physical properties of an explosive, one of the most important is its sensitiveness. It must be sufficiently sensitive to be fired with certainty by the means to be used, but up to this limit the less sensitive it is, the safer and therefore the better it is. An explosive that is very sensi­ tive to blow or friction is too dangerous for use. The hardness, consistency and form of grain are all of importance as they affect the explosive properties. Other important properties are the power and violence of the explosive. The power is the quantity of work that the explosive can do. The violence depends not only on the power, but also on the time in which the energy is set free. All these matters will be discussed in the following pages in which technical details will be avoided as far as possible. For fuller information I would refer the reader to my larger work on Explosives, their History and Manu­ facture, Properties and Tests.1 1 1 J. & A. Churchill—2nd Edition, 1917. CH APTER II BLACK POWDER AND SIMILAR MIXTURES Gunpowder, otherwise black powder, is by far the oldest of all explosives. It seems to have been made and used first in the East in the first half of the thirteenth century. It is a mixture of saltpetre, charcoal and sulphur., Of these charcoal, formed by heating wood, must have been familiar to man from the very earliest times. Sulphur occurs in the native state in various volcanic regions, especially in Sicily, and can be refined fairly well by merely melting it and running it off from the earthy matter. Saltpetre also occurs naturally in the salty efflorescences that are formed on the surface of the ground in places where there is little or no rainfall during a considerable portion of the year. But saltpetre is only one of many substances that may be present in these efflorescences, and a considerable amount of knowledge and experi­ ence were required before it was possible to recognise the substance and separate it in a state of sufficient purity. The discovery of gunpowder is therefore intimately connected with that of saltpetre. It appears to have been made first in China, but knowledge of it spread rapidly to the West, being carried perhaps by the armies of the Mongols, which in the thirteenth century overran Asia from China to Mesopotamia and Russia. From there it was carried by the Arabs through Egypt and Northern Africa to Spain, and so the secret was learnt by Europeans. From the writings of Roger Bacon about the year 1250 it is evident that he was familiar with gunpowder and some of its properties. The early history of this subject is, however, far from clear, for many of the statements are purposely obscure, and most of the words used in the various languages as names of gunpowder, saltpetre, etc., had previously been employed in other senses. At first gunpowder was only used for making fireworks, such as squibs, and perhaps incendiary mixtures. In warfare these were probably effective in frightening the enemy rather than in doing him real injury. The further step of using gunpowder to drive a missile from a fire-arm does not appear to have been made until some time in the first half of the fourteenth century. This invention required a considerable degree of engineering skill. It has often been ascribed to a German monk called Bert- hold Schwartz, but nothing is known with certainty of this individual, and the dates given vary considerably, but are all in the second half of the four- 3 4 A SHORT ACCOUNT OF EXPLOSIVES teenth century and are consequently all too late. By the middle of this century all the countries of Western Europe seem to have possessed fire-arms, but of course they were of a very rudimentary description. In the course of the following centuries the methods of manufacture of gunpowder were gradually improved. At first the three ingredients, with or without other additions, were simply pounded up together in a mortar. As the scale of manufacture increased the occurrence of serious accidents rendered it necessary to erect special powder mills remote from dwelling- houses. The composition of the powder, which was at first very variable, gradually became fixed at about 75 per cent, saltpetre. In England and France respectively the standard mixtures are: England . France Saltpetre.. .... 75 75 Sulphur . 1 0 12*5 Charcoal . 1 5 12-5 In the other countries the compositions are very similar. The preparation of the ingredients was also gradually perfected and became standardised more or less. The charcoal for the best sorts of gun­ powder is made by heating selected sorts of wood in iron cylinders with only small openings to permit the escape of the gases and vapours. Dogwood, alder and willow are those most used. The sulphur is refined by distilling it, collecting it in the molten state and casting it into sticks or “ rolls.’’ “ Flowers of sulphur,” the small crystals obtained by subliming sulphur, are not used for the manufacture of good class explosives, as they always contain acid. Until recently nearly the whole of the world’s supply of sulphur came from Sicily from the slopes of Mount Etna, but now very large quantities are obtained from Louisiana in the United States, where it is worked by the ingenious Frasch process.

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