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A number of 1.25lb M112 Demolition Charges, consisting of a C-4 compound, sit atop degraded weaponry scheduled for destruction

An explosive material, also called an explosive, is a substance that contains a great amount of stored energy that can produce an explosion, a sudden expansion of the material after initiation, usually accompanied by the production of light, heat, and pressure. An explosive charge is a measured quantity of explosive material.

The energy stored in an explosive material may be

Explosive materials may be categorized by the speed at which they expand. Materials that detonate (explode faster than the speed of sound) are said to be high explosives and materials that deflagrate are said to be low explosives. Explosives may also be categorized by their sensitivity. Sensitive materials that can be initiated by a relatively small amount of heat or pressure are primary explosives and materials that are relatively insensitive are secondary explosives.

Contents

Type of reaction

There are different reasons and conditions that make a material explosive. Explosive material is often classified by the type of reaction that takes place.

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Chemical

Chemical explosives are substances that contain a large amount of energy stored in chemical bonds.

Explosives are classified as low or high explosives according to their rates of burn: low explosives burn rapidly (or deflagrate), while high explosives detonate. While these definitions are distinct, the problem of precisely measuring rapid decomposition makes practical classification of explosives difficult.

Decomposition

The chemical decomposition of an explosive may take years, days, hours, or a fraction of a second. The slower processes of decomposition take place in storage and are of interest only from a stability standpoint. Of more interest are the two rapid forms of decomposition, deflagration and detonation.

Deflagration

In deflagration, the decomposition of the explosive material is propagated by a flame front, which moves slowly through the explosive material in contrast to detonation. Deflagration is a characteristic of low explosive material.

Detonation

The latter term is used to describe an explosive phenomenon whereby the decomposition is propagated by the explosive shockwave traversing the explosive material. The shockwave front is capable of passing through the high explosive material at great speeds, typically thousands of meters per second.

Mechanical

Exotic

In addition to chemical explosives, there exist varieties of more exotic explosive material, and theoretical methods of causing explosions. Examples include nuclear explosives, antimatter, and abruptly heating a substance to a plasma state with a high-intensity laser or electric arc.

Properties of explosive materials

To determine the suitability of an explosive substance for a particular use, its physical properties must first be investigated. The usefulness of an explosive can only be appreciated when the properties and the factors affecting them are fully understood. Some of the more important characteristics are discussed below:

Availability and cost

Availability and cost of explosives is determined by the availability of the raw materials and the cost, complexity, and safety of the manufacturing operations.

Sensitivity

Regarding an explosive, this refers to the ease with which it can be ignited or detonated—i.e., the amount and intensity of shock, friction, or heat that is required. When the term sensitivity is used, care must be taken to clarify what kind of sensitivity is under discussion. The relative sensitivity of a given explosive to impact may vary greatly from its sensitivity to friction or heat. Some of the test methods used to determine sensitivity are as follows:

  • Impact Sensitivity is expressed in terms of the distance through which a standard weight must be dropped to cause the material to explode.
  • Friction Sensitivity is expressed in terms of what occurs when a weighted pendulum scrapes across the material (snaps, crackles, ignites, and/or explodes).
  • Heat Sensitivity is expressed in terms of the temperature at which flashing or explosion of the material occurs.

Sensitivity is an important consideration in selecting an explosive for a particular purpose. The explosive in an armor-piercing projectile must be relatively insensitive, or the shock of impact would cause it to detonate before it penetrated to the point desired. The explosive lenses around nuclear charges are also designed to be highly insensitive, to minimize the risk of accidental detonation.

Sensitivity to initiation

Is the index of the capacity of the explosive to be initiated into detonation in a sustained manner. It is defined by the power of the detonator which is certain to prime the explosive to a sustained and continuous detonation. Reference is made to the Sellier-Bellot scale that consists of a series of 10 detonators, from n. 1 to n. 10, each of which corresponds to an increasing charge weight. In practice most of the explosives on the market today are sensitive to the n. 8 detonator, where the charge corresponds to 2 grams of fulminate of mercury.

Velocity of detonation

Is the velocity with which the reaction process propagates in the mass of the explosive. Most commercial mining explosives have detonation velocities ranging from 1800 m/s to 8000 m/s. Today, velocity of detonation can be measured with accuracy. Together with density it is an important element influencing the yield of the energy transmitted (for both, atmospheric overpressure and ground acceleration).

Stability

Stability is the ability of an explosive to be stored without deterioration.

The following factors affect the stability of an explosive:

  • Chemical constitution. The very fact that some common chemical compounds can undergo explosion when heated indicates that there is something unstable in their structures. While no precise explanation has been developed for this, it is generally recognized that certain radical groups, nitrite (–NO2), nitrate (–NO3), and azide (–N3), are intrinsically in a condition of internal strain. Increasing the strain by heating can cause a sudden disruption of the molecule and consequent explosion. In some cases, this condition of molecular instability is so great that decomposition takes place at ordinary temperatures.
  • Temperature of storage. The rate of decomposition of explosives increases at higher temperatures. All of the standard military explosives may be considered to have a high degree of stability at temperatures of -10 to +35 °C, but each has a high temperature at which the rate of decomposition rapidly accelerates and stability is reduced.As a rule of thumb, most explosives become dangerously unstable at temperatures exceeding 70 °C.
  • Exposure to the sun. If exposed to the ultraviolet rays of the sun, many explosive compounds that contain nitrogen groups will rapidly decompose, affecting their stability.
  • Electrical discharge. Electrostatic or spark sensitivity to initiation is common to a number of explosives. Static or other electrical discharge may be sufficient to inspire detonation under some circumstances. As a result, the safe handling of explosives and pyrotechnics almost always requires electrical grounding of the operator.

Power

The term power or performance as applied to an explosive refers to its ability to do work. In practice it is defined as the explosive's ability to accomplish what is intended in the way of energy delivery (i.e., fragment projection, air blast, high-velocity jets, underwater shock and bubble energy, etc.). Explosive power or performance is evaluated by a tailored series of tests to assess the material for its intended use. Of the tests listed below, cylinder expansion and air-blast tests are common to most testing programs, and the others support specific applications.

  • Cylinder expansion test. A standard amount of explosive is loaded into a long hollow cylinder, usually of copper, and detonated at one end. Data is collected concerning the rate of radial expansion of the cylinder and maximum cylinder wall velocity. This also establishes the Gurney energy or 2E.
  • Cylinder fragmentation. A standard steel cylinder is loaded with explosive and detonated in a sawdust pit. The fragments are collected and the size distribution analyzed.
  • Detonation pressure (Chapman-Jouguet condition). Detonation pressure data derived from measurements of shock waves transmitted into water by the detonation of cylindrical explosive charges of a standard size.
  • Determination of critical diameter. This test establishes the minimum physical size a charge of a specific explosive must be to sustain its own detonation wave. The procedure involves the detonation of a series of charges of different diameters until difficulty in detonation wave propagation is observed.
  • Infinite-diameter detonation velocity. Detonation velocity is dependent on loading density (c), charge diameter, and grain size. The hydrodynamic theory of detonation used in predicting explosive phenomena does not include diameter of the charge, and therefore a detonation velocity, for an imaginary charge of Infinite diameter. This procedure requires a series of charges of the same density and physical structure, but different diameters, to be fired and the resulting detonation velocities extrapolated to predict the detonation velocity of a charge of infinite diameter.
  • Pressure versus scaled distance. A charge of specific size is detonated and its pressure effects measured at a standard distance. The values obtained are compared with that for TNT.
  • Impulse versus scaled distance. A charge of specific size is detonated and its impulse (the area under the pressure-time curve) measured versus distance. The results are tabulated and expressed in TNT equivalent.
  • Relative bubble energy (RBE). A 5- to 50 kg charge is detonated in water and piezoelectric gauges measure peak pressure, time constant, impulse, and energy.
The RBE may be defined as Kx 3
RBE = Ks
where K = bubble expansion period for experimental (x) or standard (s) charge.

Brisance

In addition to strength, explosives display a second characteristic, which is their shattering effect or brisance (from the French meaning to "break"), which is distinguished from their total work capacity. An exploding propane tank may release more chemical energy than an ounce of nitroglycerin, but the tank would probably fragment into large pieces of twisted metal, while a metal casing around the nitroglycerin would be pulverized. This characteristic is of practical importance in determining the effectiveness of an explosion in fragmenting shells, bomb casings, grenades, and the like. The rapidity with which an explosive reaches its peak pressure (power) is a measure of its brisance. Brisance values are primarily employed in France and Russia.

The sand crush test is commonly employed to determine the relative brisance in comparison to TNT. No test is capable of directly comparing the explosive properties of two or more compounds; it is important to examine the data from several such tests (sand crush, trauzl, and so forth) in order to gauge relative brisance. True values for comparison will require field experiments.

Density

Density of loading refers to the mass of an explosive per unit volume. Several methods of loading are available, including pellet loading, cast loading, and press loading; the one used is determined by the characteristics of the explosive. Dependent upon the method employed, an average density of the loaded charge can be obtained that is within 80–99% of the theoretical maximum density of the explosive. High load density can reduce sensitivity by making the mass more resistant to internal friction. However, if density is increased to the extent that individual crystals are crushed, the explosive may become more sensitive. Increased load density also permits the use of more explosive, thereby increasing the power of the warhead. It is possible to compress an explosive beyond a point of sensitivity, known also as "dead-pressing", in which the material is no longer capable of being reliably initiated, if at all.

Volatility

Volatility is the readiness with which a substance vaporizes. Excessive volatility often results in the development of pressure within rounds of ammunition and separation of mixtures into their constituents. Volatility affects the chemical composition of the explosive such that a marked reduction in stability may occur, which results in an increase in the danger of handling.

Hygroscopicity and water resistance

The introduction of water into an explosive is highly undesirable since it reduces the sensitivity, strength, and velocity of detonation of the explosive. Hygroscopicity is used as a measure of a material's moisture-absorbing tendencies. Moisture affects explosives adversely by acting as an inert material that absorbs heat when vaporized, and by acting as a solvent medium that can cause undesired chemical reactions. Sensitivity, strength, and velocity of detonation are reduced by inert materials that reduce the continuity of the explosive mass. When the moisture content evaporates during detonation, cooling occurs, which reduces the temperature of reaction. Stability is also affected by the presence of moisture since moisture promotes decomposition of the explosive and, in addition, causes corrosion of the explosive's metal container.

Explosives considerably differ from one another as to their behavior in the presence of water. Gelatin dynamites containing nitroglycerine have a degree of water resistance. Explosives based on ammonium nitrate have little or no water resistance.

Toxicity

Due to their chemical structure, most explosives are toxic to some extent. Explosive product gases can also be toxic.

Explosive train

Another property of explosive material is where it exists in the explosive train of the device or system. An example of this is a pyrotechnic lead igniting a booster, which causes the main charge to detonate.

Volume of products of explosion

Avogadro's law states that equal volumes of all gases under the same conditions of temperature and pressure contain the same number of molecules, that is, the molar volume of one gas is equal to the molar volume of any other gas. The molar volume of any gas at 0°C and under normal atmospheric pressure is very nearly 22.4 liters. Thus, considering the nitroglycerin reaction,

C3H5(NO3)3 → 3CO2 + 2.5H2O + 1.5N2 + 0.25O2

the explosion of one mole of nitroglycerin produces 3 moles of CO2, 2.5 moles of H2O, 1.5 moles of N2, and 0.25 mole of O2, all in the gaseous state. Since a molar volume is the volume of one mole of gas, one mole of nitroglycerin produces 3 + 2.5 + 1.5 + 0.25 = 7.25 molar volumes of gas; and these molar volumes at 0°C and atmospheric pressure form an actual volume of 7.25 × 22.4 = 162.4 liters of gas.

Based upon this simple beginning, it can be seen that the volume of the products of explosion can be predicted for any quantity of the explosive. Further, by employing Charles' Law for perfect gases, the volume of the products of explosion may also be calculated for any given temperature. This law states that at a constant pressure a perfect gas expands 1/273.15 of its volume at 0 °C, for each degree Celsius of rise in temperature.

Therefore, at 15 °C (288.15 kelvin) the molar volume of an ideal gas is

V15 = 22.414 (288.15/273.15) = 23.64 liters per mole

Thus, at 15 °C the volume of gas produced by the explosive decomposition of one mole of nitroglycerin becomes

V = (23.64 l/mol)(7.25 mol) = 171.4 l

Explosive strength

The potential of an explosive is the total work that can be performed by the gas resulting from its explosion, when expanded adiabatically from its original volume, until its pressure is reduced to atmospheric pressure and its temperature to 15 °C. The potential is therefore the total quantity of heat given off at constant volume when expressed in equivalent work units and is a measure of the strength of the explosive.

Oxygen balance (OB% or Ω)

Oxygen balance is an expression that is used to indicate the degree to which an explosive can be oxidized. If an explosive molecule contains just enough oxygen to convert all of its carbon to carbon dioxide, all of its hydrogen to water, and all of its metal to metal oxide with no excess, the molecule is said to have a zero oxygen balance. The molecule is said to have a positive oxygen balance if it contains more oxygen than is needed and a negative oxygen balance if it contains less oxygen than is needed. [1] The sensitivity, strength, and brisance of an explosive are all somewhat dependent upon oxygen balance and tend to approach their maximums as oxygen balance approaches zero.

Chemical composition

A chemical explosive may consist of either a chemically pure compound, such as nitroglycerin, or a mixture of an fuel and a oxidizer, such as black powder or grain dust and air.

Chemically pure compounds

Some chemical compounds are unstable in that, when shocked, they react, possibly to the point of detonation. Each molecule of the compound dissociates into two or more new molecules (generally gases) with the release of energy.

  • Nitroglycerin: A highly unstable and sensitive liquid.
  • Acetone peroxide: A very unstable white organic peroxide.
  • TNT: Yellow insensitive crystals that can be melted and cast without detonation.
  • Nitrocellulose: A nitrated polymer which can be a high or low explosive depending on nitration level and conditions.
  • RDX, PETN, HMX: Very powerful explosives which can be used pure or in plastic explosives.

The above compositions may describe the majority of the explosive material, but a practical explosive will often include small percentages of other materials. For example, dynamite is a mixture of highly sensitive nitroglycerin with sawdust, powdered silica, or most commonly diatomaceous earth, which act as stabilizers. Plastics and polymers may be added to bind powders of explosive compounds; waxes may be incorporated to make them safer to handle; aluminium powder may be introduced to increase total energy and blast effects. Explosive compounds are also often "alloyed": HMX or RDX powders may be mixed (typically by melt-casting) with TNT to form Octol or Cyclotol.

Mixture of oxidizer and fuel

An oxidizer is a pure substance (molecule) that in a chemical reaction can contribute some atoms of one or more oxidizing elements, in which the fuel component of the explosive burns. On the simplest level, the oxidizer may itself be an oxidizing element, such as gaseous or liquid oxygen.

Classification of explosive materials

By sensitivity

Primary explosive

A primary explosive is an explosive that is extremely sensitive to stimuli such as impact, friction, heat, static electricity, or electromagnetic radiation. A relatively small amount of energy is required for initiation. As a very general rule, primary explosives are considered to be those compounds that are more sensitive than PETN. As a practical measure, primary explosives are sufficiently sensitive that they can be reliably initiated with a blow from a hammer; however, PETN can usually be initiated in this manner, so this is only a very broad guideline. Additionally, several compounds, such as nitrogen triiodide, are so sensitive that they cannot even be handled without detonating.

Primary explosives are often used in detonators or to trigger larger charges of less sensitive secondary explosives. primary explosives are commonly used in blasting caps to translate a signal (electrical, shock, or in the case of laser detonation systems, light) into an action, i.e., an explosion. A small quantity—usually milligrams—is sufficient to initiate a larger charge of explosive that is usually safer to handle.[2]

Examples of primary high explosives are:

Secondary explosive

A secondary explosive is less sensitive than a primary explosive and require substantially more energy to be initiated. Because they are less sensitive they are usable in a wider variety of applications and are safer to handle and store. Secondary explosives are used in larger quantities in an explosive train and are usually initiated by a smaller quantity of a primary explosive.

Examples of secondary explosives include TNT and RDX.

By velocity

Low explosives

Low explosives are compounds where the rate of decomposition proceeds through the material at less than the speed of sound. The decomposition is propagated by a flame front (deflagration) which travels much more slowly through the explosive material than a shock wave of a high explosive. Under normal conditions, low explosives undergo deflagration at rates that vary from a few centimeters per second to approximately 400 metres per second. It is possible for them to deflagrate very quickly, producing an effect similar to a detonation. This can happen under higher pressure or temperature, which usually occurs when ignited in a confined space.

A low explosive is usually a mixture of a combustible substance and an oxidant that decomposes rapidly (deflagration), however they burn slower than a high explosive which has an extremely fast burn rate.

Low explosives are normally employed as propellants. Included in this group are gun powders and light pyrotechnics, such as flares and fireworks.

High explosives

High explosives are explosive materials that detonate, meaning that the explosive shock front passes though the material at a supersonic speed. High explosives detonate with explosive velocity rates ranging from 3,000 to 9,000 meters per second. They are normally employed in mining, demolition, and military applications. They can be divided into two explosives classes differentiated by sensitivity: Primary explosive and secondary explosive. The term high explosive is in contrast to the term low explosive, which explodes (deflagrates) at a slower rate.

By composition

Priming composition

Priming compositions are primary explosives mixed with other compositions to control (lessen) the sensitivity of the mixture to the desired property.

For example, primary explosives are so sensitive that they need to be stored and shipped in a wet state to prevent accidental initiation.

Shipping label classifications

Shipping labels and tags may include both United Nations and national markings.

United Nations markings include numbered Hazard Class and Division (HC/D) codes and alphabetic Compatibility Group codes. Though the two are related, they are separate and distinct. Any Compatibility Group designator can be assigned to any Hazard Class and Division. An example of this hybrid marking would be a consumer firework, which is labeled as 1.4G or 1.4S.

Examples of national markings would include United States Department of Transportation (U.S. DOT) codes.

United Nations Organization (UNO) Hazard Class and Division (HC/D)

Explosives warning sign

The Hazard Class and Division (HC/D) is a numeric designator within a hazard class indicating the character, predominance of associated hazards, and potential for causing personnel casualties and property damage. It is an internationally accepted system that communicates the primary hazard associated with a substance using the minimum amount of markings.[4]

Listed below are the Divisions for Class 1 (Explosives):

  • 1.1 Mass Detonation Hazard. With HC/D 1.1, it is expected that if one item in a container or pallet inadvertently detonates, the explosion will sympathetically detonate the surrounding items. The explosion could propagate to all or the majority of the items stored together causing a mass detonation. There will also be fragments from the item’s casing and/or structures in the blast area.
  • 1.2 Non-mass explosion, fragment-producing. HC/D 1.2 is further divided into three subdivisions, HC/D 1.2.1, 1.2.2 and 1.2.3, to account for the magnitude of the effects of an explosion.
  • 1.3 Mass fire, minor blast or fragment hazard. Propellants and many of the pyrotechnic items fall into this category. If one item in a package or stack initiates, it will usually propagate to the other items creating a mass fire.
  • 1.4 Moderate fire, no blast or fragment. HC/D 1.4 items are listed in the table as explosives with no significant hazard. Most small arms and some pyrotechnic items fall into this category. If the energetic material in these items inadvertently initiates, most of the energy and fragments will be contained within the storage structure or the item containers themselves.
  • 1.5 mass detonation hazard, very insensitive (with a )
  • 1.6 detonation hazard without mass detonation hazard, extremely insensitive.

To see an entire UNO Table, browse Para 3-8 and 3-9 from the NAVSEA OP 5, Vol. 1, Chapter 3.

Class 1 Compatibility Group

Compatibility Group codes are used to indicate storage compatibility for HC/D Class 1 (explosive) materials. Letters are used to designate 13 compatibility groups as follows.

A: Primary explosive substance (1.1A).

B: An article containing a primary explosive substance and not containing two or more effective protective features. Some articles, such as detonator assemblies for blasting and primers, cap-type, are included. (1.1B, 1.2B, 1.4B).

C: Propellant explosive substance or other deflagrating explosive substance or article containing such explosive substance (1.1C, 1.2C, 1.3C, 1.4C). These are bulk propellants, propelling charges, and devices containing propellants with or without means of ignition. Examples include single-, double-, triple-based, and composite propellants, solid propellant rocket motors and ammunition with inert projectiles.

D: Secondary detonating explosive substance or black powder or article containing a secondary detonating explosive substance, in each case without means of initiation and without a propelling charge, or article containing a primary explosive substance and containing two or more effective protective features. (1.1D, 1.2D, 1.4D, 1.5D).

E: Article containing a secondary detonating explosive substance without means of initiation, with a propelling charge (other than one containing flammable liquid, gel or hypergolic liquid) (1.1E, 1.2E, 1.4E).

F containing a secondary detonating explosive substance with its means of initiation, with a propelling charge (other than one containing flammable liquid, gel or hypergolic liquid) or without a propelling charge (1.1F, 1.2F, 1.3F, 1.4F).

G: Pyrotechnic substance or article containing a pyrotechnic substance, or article containing both an explosive substance and an illuminating, incendiary, tear-producing or smoke-producing substance (other than a water-activated article or one containing white phosphorus, phosphide or flammable liquid or gel or hypergolic liquid) (1.1G, 1.2G, 1.3G, 1.4G). Examples include Flares, signals, incendiary or illuminating ammunition and other smoke and tear producing devices.

H: Article containing both an explosive substance and white phosphorus (1.2H, 1.3H). These articles will spontaneously combust when exposed to the atmosphere.

J: Article containing both an explosive substance and flammable liquid or gel (1.1J, 1.2J, 1.3J). This excludes liquids or gels which are spontaneously flammable when exposed to water or the atmosphere, which belong in group H. Examples include liquid or gel filled incendiary ammunition, fuel-air explosive (FAE) devices, and flammable liquid fueled missiles.

K: Article containing both an explosive substance and a toxic chemical agent (1.2K, 1.3K)

L Explosive substance or article containing an explosive substance and presenting a special risk (e.g., due to water-activation or presence of hypergolic liquids, phosphides, or pyrophoric substances) needing isolation of each type (1.1L, 1.2L, 1.3L). Damaged or suspect ammunition of any group belongs in this group.

N: Articles containing only extremely insensitive detonating substances (1.6N).

S: Substance or article so packed or designed that any hazardous effects arising from accidental functioning are limited to the extent that they do not significantly hinder or prohibit fire fighting or other emergency response efforts in the immediate vicinity of the package (1.4S).

Legacy article contents

Contents below this heading have not been incorporated into the regrouped article.

Chemical explosives

Explosives usually have less potential energy than petroleum fuels, but their high rate of energy release produces a great blast pressure. TNT has a detonation velocity of 6,940 m/s compared to 1,680 m/s for the detonation of a pentane-air mixture, and the 0.34-m/s stoichiometric flame speed of gasoline combustion in air.

The properties of the explosive indicate the class into which it falls. In some cases explosives can be made to fall into either class by the conditions under which they are initiated. In sufficiently large quantities, almost all low explosives can undergo a Deflagration to Detonation Transition (DDT). For convenience, low and high explosives may be differentiated by the shipping and storage classes.

Chemical explosive reaction

A chemical explosive is a compound or mixture which, upon the application of heat or shock, decomposes or rearranges with extreme rapidity, yielding much gas and heat. Many substances not ordinarily classed as explosives may do one, or even two, of these things. For example, at high temperatures (> 2000°C) a mixture of nitrogen and oxygen can be made to react with great rapidity and yield the gaseous product nitric oxide; yet the mixture is not an explosive since it does not evolve heat, but rather absorbs heat.

N2 + O2 → 2 NO − 43,200 calories (or 180 kJ) per mole of N2

For a chemical to be an explosive, it must exhibit all of the following:

  • Rapid expansion (i.e., rapid production of gases or rapid heating of surroundings)
  • Evolution of heat
  • Rapidity of reaction
  • Initiation of reaction

Sensitiser

A sensitiser is a powdered or fine particulate material that is sometimes used to create voids that aid in the initiation or propagation of the detonation wave. It may be as high-tech as glass beads or as simple as seeds.

Measurement of chemical explosive reaction

The development of new and improved types of ammunition requires a continuous program of research and development. Adoption of an explosive for a particular use is based upon both proving ground and service tests. Before these tests, however, preliminary estimates of the characteristics of the explosive are made. The principles of thermochemistry are applied for this process.

Thermochemistry is concerned with the changes in internal energy, principally as heat, in chemical reactions. An explosion consists of a series of reactions, highly exothermic, involving decomposition of the ingredients and recombination to form the products of explosion. Energy changes in explosive reactions are calculated either from known chemical laws or by analysis of the products.

For most common reactions, tables based on previous investigations permit rapid calculation of energy changes. Products of an explosive remaining in a closed calorimetric bomb (a constant-volume explosion) after cooling the bomb back to room temperature and pressure are rarely those present at the instant of maximum temperature and pressure. Since only the final products may be analyzed conveniently, indirect or theoretical methods are often used to determine the maximum temperature and pressure values.

Some of the important characteristics of an explosive that can be determined by such theoretical computations are:

  • Oxygen balance
  • Heat of explosion or reaction
  • Volume of products of explosion
  • Potential of the explosive

Balancing chemical explosion equations

In order to assist in balancing chemical equations, an order of priorities is presented in table 1. Explosives containing C, H, O, and N and/or a metal will form the products of reaction in the priority sequence shown. Some observation you might want to make as you balance an equation:

  • The progression is from top to bottom; you may skip steps that are not applicable, but you never back up.
  • At each separate step there are never more than two compositions and two products.
  • At the conclusion of the balancing, elemental nitrogen, oxygen, and hydrogen are always found in diatomic form.
Table 1. Order of Priorities
Priority Composition of explosive Products of decomposition Phase of products
1
A metal and chlorine Metallic chloride
Solid
2
Hydrogen and chlorine HCl
Gas
3
A metal and oxygen Metallic oxide
Solid
4
Carbon and oxygen CO
Gas
5
Hydrogen and oxygen H2O
Gas
6
Carbon monoxide and oxygen CO2
Gas
7
Nitrogen N2
Gas
8
Excess oxygen O2
Gas
9
Excess hydrogen H2
Gas
10
Excess carbon C
Solid

Example, TNT:

C6H2(NO2)3CH3; → : 7C + 5H + 3N + 6O

Using the order of priorities in table 1, priority 4 gives the first reaction products:

7C + 6O → 6CO with one mol of carbon remaining

Next, since all the oxygen has been combined with the carbon to form CO, priority 7 results in:

3N → 1.5N2

Finally, priority 9 results in: 5H → 2.5H2

The balanced equation, showing the products of reaction resulting from the detonation of TNT is:

C6H2(NO2)3CH3 → 6CO + 2.5H2 + 1.5N2 + C

Notice that partial moles are permitted in these calculations. The number of moles of gas formed is 10. The product carbon is a solid.

Example of thermochemical calculations

The PETN reaction will be examined as an example of thermo-chemical calculations.

PETN: C(CH2ONO2)4
Molecular weight = 316.15 g/mol
Heat of formation = 119.4 kcal/mol

(1) Balance the chemical reaction equation. Using table 1, priority 4 gives the first reaction products:

5C + 12O → 5CO + 7O

Next, the hydrogen combines with remaining oxygen:

8H + 7O → 4H2O + 3O

Then the remaining oxygen will combine with the CO to form CO and CO2.

5CO + 3O → 2CO + 3CO2

Finally the remaining nitrogen forms in its natural state (N2).

4N → 2N2

The balanced reaction equation is:

C(CH2ONO2)4 → 2CO + 4H2O + 3CO2 + 2N2

(2) Determine the number of molar volumes of gas per mole. Since the molar volume of one gas is equal to the molar volume of any other gas, and since all the products of the PETN reaction are gaseous, the resulting number of molar volumes of gas (Nm) is:

Nm = 2 + 4 + 3 + 2 = 11 Vmolar/mol

(3) Determine the potential (capacity for doing work). If the total heat liberated by an explosive under constant volume conditions (Qm) is converted to the equivalent work units, the result is the potential of that explosive.

The heat liberated at constant volume (Qmv) is equivalent to the heat liberated at constant pressure (Qmp) plus that heat converted to work in expanding the surrounding medium. Hence, Qmv = Qmp + work (converted).

a. Qmp = Qfi (products) − Qfk (reactants)
where: Qf = heat of formation (see table 1)
For the PETN reaction:
Qmp = 2(26.343) + 4(57.81) + 3(94.39) − (119.4) = 447.87 kcal/mol
(If the compound produced a metallic oxide, that heat of formation would be included in Qmp.)
b. Work = 0.572Nm = 0.572(11) = 6.292 kcal/mol
As previously stated, Qmv converted to equivalent work units is taken as the potential of the explosive.
c. Potential J = Qmv (4.185 × 106 kg)(MW) = 454.16 (4.185 × 106) 316.15 = 6.01 × 106 J kg
This product may then be used to find the relative strength (RS) of PETN, which is
d. RS = Pot (PETN) = 6.01 × 106 = 2.21 Pot (TNT) 2.72 × 106

History

Though early thermal weapons, such as Greek fire, have existed since ancient times, the first widely used explosive in warfare and mining was black powder, invented in 9th century China; see the history of gunpowder. This material was sensitive to water, and evolved lots of dark smoke. During the 19th century black powder was replaced by nitroglycerine, nitrocellulose, smokeless powder, dynamite and gelignite (the two latter invented by Alfred Nobel). World War II saw an extensive use of new explosives, see explosives used during World War II. In turn, these have largely been replaced by modern explosives such as trinitrotoluene and C-4.

The increased availability of chemicals has allowed the construction of improvised explosive devices.

Legal status

The legality of possessing or using explosives varies by jurisdiction. In the United States, these acts are governed by the Importation, Manufacture, Distribution and Storage of Explosive Materials (18 U.S.C. Chapter 40).[5]

USA

New York

In the State of New York, health and safety regulations restrict the quantity of black powder a person may store and transport.[6] Florida also has some up-tight rules about Explosives and their transportation.

See also

Notes

  1. ^ Meyer, Rudolf; Josef Köhler, Axel Homburg (2007). Explosives, 6th Ed.. Wiley VCH. ISBN 3-527-31656-6. 
  2. ^ Primary Explosives. Globalsecurity.org. Retrieved on 2010-02-11.
  3. ^ PowerLabs Lead Picrate Synthesis
  4. ^ Table 12-4.—United Nations Organization Hazard Classes. Tpub.com. Retrieved on 2010-02-11.
  5. ^ Federal Explosives Law and Regulations, U.S. Department of Justice, Bureau of Alcohol, Tobacco, Firearms and Explosives
  6. ^ Special provisions relating to black powder

References

  • Army Research Office. Elements of Armament Engineering (Part One). Washington, D.C.: U.S. Army Materiel Command, 1964.
  • Commander, Naval Ordnance Systems Command. Safety and Performance Tests for Qualification of Explosives. NAVORD OD 44811. Washington, D.C.: GPO, 1972.
  • Commander, Naval Ordnance Systems Command. Weapons Systems Fundamentals. NAVORD OP 3000, vol. 2, 1st rev. Washington, D.C.: GPO, 1971.
  • Departments of the Army and Air Force. Military Explosives. Washington, D.C.: 1967.
  • USDOT Hazardous Materials Transportation Placards
  • Swiss Agency for the Environment, Forests, and Landscap. "Occurrence and relevance of organic pollutants in compost, digestate and organic residues", Research for Agriculture and Nature. 8 November 2004. p 52, 91, 182.

External links


1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

EXPLOSIVES, a general term for substances which by certain treatment "explode," i.e. decompose or change in a violent manner so as to generate force. From the manner and degree of violence of the decomposition they are classified into "propellants" and "detonators," but this classification is not capable of sharp delimitation. In some cases the same substance may be employed for either purpose under altered external conditions; but there are some substances which could not possibly be employed as propellants, and others which can scarcely be induced to explode in the manner known as "detonation." A propellant may be considered as a substance that on explosion produces such a disturbance that neighbouring substances are thrown to some distance; a detonator or disruptor may produce an extremely violent disturbance within a limited area without projecting substances to any great distance. Time is an important, perhaps the most important, factor in this action. A propellant generally acts by burning in a more or less rapid and regular manner, producing from a comparatively small volume a large volume of gases; during this action heat is also developed, which, being expended mostly on the gaseous products, causes a further expansion. The noise accompanying an explosion is due to an air wave, and is markedly different in the case of a detonator from a real propellant. Some cases of ordinary combustion can be accelerated into explosions by increasing the area of contact between the combustible and the oxygen supplier, for instance, ordinary gas or dust explosions. Neither temperature nor quantity of heat energy necessarily gives an explosive action. Some metals, e.g. aluminium and magnesium, will, in oxidizing, produce a great thermal effect, but unless there be some gaseous products no real explosive action.

Explosives may be mechanical mixtures of substances capable of chemical interaction with the production of large volumes of gases, or definite chemical compounds of a peculiar class known as "endothermic," the decomposition of which is also attended with the evolution of gases in large quantity.

All chemical compounds are either "endothermic" or "exothermic." In endothermic compounds energy, in some form, has been taken up in the act of formation of the compound. Some of this energy has become potential, or rather the compound formed has been raised to a higher potential. This case occurs when two elements can be united only under some compulsion such as a very high temperature, by the aid of an electric current, or spark, or as a secondary product whilst some other reactions are proceeding. For example, oxygen and nitrogen combine only under the influence of an electric spark, and carbon and calcium in the electric furnace. The formation of chlorates by the action of chlorine on boiling potash is a good instance of a complex compound (potassium chlorate), being formed in small quantity as a secondary product whilst a large quantity of primary and simpler products (potassium chloride and water) is forming. In chlorate formation the greater part of the reaction represents a running down of energy and formation of exothermic compounds, with only a small yield of an endothermic substance. Another idea of the meaning of endothermic is obtained from acetylene. When 26 parts by weight of this substance are burnt, the heat produced will warm up 310,450 parts of water I° C. Acetylene consists of 24 parts of carbon and 2 of hydrogen by weight. The 24 parts of carbon will, if in the form of pure charcoal, heat 192,000 parts of water 0, and the 2 parts of hydrogen will heat 68,000 parts of water 1 °, the total heat production being 260,000 heat units. Thus 26 grams of acetylene give an excess of 50,450 units over the amount given by the constituents. This excess of heat energy 1 is due to some form of potential energy in the compound which becomes actual heat energy at the moment of dissolution of the chemical union. The manner in which a substance is endothermic is of importance as regards the practical employment of explosives. Some particular endothermic state or form results from the mode of formation and the consequent internal structure of the molecule. Physical structure alone can be the cause of a relative endothermic state, as in the glass bulbs known as Rupert's drops, &c., or even in chilled steel. Rupert's drops fly in pieces on being scratched or cut to a certain depth. The cause is undoubtedly to be ascribed to the molecular state of the glass brought about by chilling from the melted state. The molecules have not had time to separate or arrange themselves in easy positions. In steel when melted the carbide of iron is no doubt diffused equally throughout the liquid. When cooled slowly some carbide separates out more or less, and the steel is soft or annealed. When chilled the carbides are retained in solid solution. The volume of chilled glass or steel differs slightly from that in the annealed state.

Superfused substances are probably in a similar state of physical potential or strain. Many metallic salts, and organic compounds especially, will exhibit this state when completely melted and then allowed to cool in a clean atmosphere. On touching with a little of the same substance in a solid state the liquids will begin to crystallize, at the same time becoming heated almost up to their melting-points. The metal gallium shows this excellently well, keeping liquid for years until touched with the solid metal, when there is a considerable rise of temperature as solidification takes place.

All carbon compounds, excepting carbon dioxide, and many if not all compounds of nitrogen, are endothermic. Most of the explosives in common use contain nitrogen in some form.

Exothermic compounds are in a certain sense the reverse of endothermic; they are relatively inert and react but slowly or not at all, unless energy be expended upon them from outside. Water, carbon dioxide and most of the common minerals belong to this class.

The explosives actually employed at the present time include mixtures, such as gunpowders and some chlorate compositions, the ingredients of which separately may be non-explosive; compounds used singly, as guncotton, nitroglycerin (in the form of dynamite), picric acid (as lyddite or melinite), trinitrotoluene, nitrocresols, mercury fulminate, &c.; combinations of some explosive compounds, such as cordite and the smokeless propellants in general use for military purposes; and, finally, blasting and detonating or igniting compositions, some of which contain inert diluting materials as well as one or more high explosives. Many igniting compositions are examples of the last type, consisting of a high explosive diluted with a neutral substance, and frequently containing in addition a composition which is inflamed by the explosion of the diluted high explosive, the flame in turn igniting the actual propellant.

Table of contents

Explosive Mixtures

The explosive mixture longest known is undoubtedly gunpowder in some form - that is, a mixture of charcoal with sulphur and nitre, the last being the oxygen provider. Besides the nitrates of metals and ammonium nitrate, there is a limited number of other substances capable of serving in a sufficiently energetic manner as oxygen providers. A few chlorates, perchlorates, permanganates and chromates almost complete the list. Of these the sodium, potassium and barium chlorates are best known and have been actually tried, in admixture with some combustible substances, as practical explosives. Most other metallic chlorates are barred from practical employment owing to instability, deliquescence or other property.

Of the chlorates those of potassium and sodium are the most stable, and mixtures of either of these salts with sulphur or sulphides, phosphorus, charcoal, sugar, starch, finely-ground cellulose, coal or almost any kind of organic, i.e. carbon, compound, in certain proportions, yield an explosive mixture. In many cases these mixtures are not only fired or exploded by heating to a certain temperature, but also by quite moderate friction or percussion. Consequently there is much danger in manufacture and storage, and however these mixtures have been made up, they are quite out of the question as propellants on account of their great tendency to explode in the manner of a detonator. In addition they are not smokeless, and leave a 1 Not necessarily heat energy entirely. A number of substances - acetylides and some nitrogen compounds, such as nitrogen chloride - decompose with extreme violence, but little heat is produced.

considerable residue which in a gun would produce serious fouling.

Mixtures of chlorates with aromatic compounds such as the nitroor dinitro-benzenes or even naphthalene make very powerful blasting agents. The violent action of a chlorate mixture is due first to the rapid evolution of oxygen, and also to the fact that a chlorate can be detonated when alone. A drop of sulphuric acid will start the combustion of a chlorate mixture. In admixture with sulphur, sulphides and especially phosphorus, chlorates give extremely sensitive compositions, some of which form the basis of friction tube and firing mixtures.

Potassium and sodium perchlorates and permanganates make similar but slightly less sensitive explosive mixtures with the above-mentioned substances. Finely divided metals such as aluminium or magnesium give also with permanganates, chlorates or perchlorates sensitive and powerful explosives. Bichromates, although containing much available oxygen, form but feeble explosive mixtures, but some compounds of chromic acid with diazo compounds and some acetylides are extremely powerful as well as sensitive. Ammonium bichromate is a self-combustible after the type of ammonium nitrate, but scarcely an explosive.

Explosive Compounds

Nearly all the explosive compounds in actual use either for blasting purposes or as propellants are nitrogen compounds, and are obtained more or less directly from nitric acid. Most of the propellants at present employed consist essentially of nitrates of some organic compound, and may be viewed theoretically as nitric acid, the hydrogen of which has been replaced by a carbon complex; such compounds are expressed by M O NO 2, which indicates that the carbon group is in some manner united by means of oxygen to the nitrogen group. Guncotton and nitroglycerin are of this class. Another large class of explosives is formed by a more direct attachment of nitrogen to the carbon complex, as represented by M N02. A number of explosives of the detonating type are of this class. They contain the same proportions of oxygen and nitrogen as nitrites, but are not nitrites. They have been termed nitroderivatives for distinction. One of the simplest and longestknown members of this group is nitrobenzene, C 6 H 5 NO 2, which is employed to some extent as an explosive, being one ingredient in rack-a-rock and other blasting compositions. The dinitrobenzenes, C6H4(N02)2, made from it are solids which are somewhat extensively employed as constituents of some sporting powders, and in admixture with ammonium nitrate form a blasting powder of a "flameless" variety which is comparatively safe in dusty or "gassy" coal seams.

Picric acid or trinitrophenol, C 6 H 2. OH (NO 2) 3 is employed as a high explosive for shell, &c. It requires, however, either to be enclosed and heated, or to be started by a powerful detonator to develop its full effect. Its compounds with metals, such as the potassium salt, C 6 H 2. OK (NO 2) 3j are when dry very easily detonated by friction or percussion and always on heating, whereas picric acid itself will burn very quietly when set fire to under ordinary conditions. Trinitrotoluene, C 6H2 CH3 (N02)3, is a high explosive resembling picric acid in the manner of its explosion (to which in fact it is a rival), but differs therefrom in not forming salts with metals. The nitronaphthols, C10H6.OH N02, and higher nitration products may be counted in the list. Their salts with metals behave much like the picrates.

All these nitro compounds can be reduced by the action of nascent hydrogen to substances called amines, which are not always explosive in themselves, but in some cases can form nitrates of a self-combustible nature. Aminoacetic acid, for instance, will form a nitrate which burns rapidly but quietly, and might be employed as an explosive. By the action of nitrous acid at low temperatures on aromatic amines, e.g. aniline, C6H5N112, diazo compounds are produced. These are all highly explosive, and when in a dry state are for the most part also extremely sensitive to friction, percussion or heat. As many of these diazo compounds contain no oxygen their explosive nature must be ascribed to the peculiar state of union of the nitrogen. This state is attempted to be shown by the formulae such as, for instance, C 6 H 5 N:N X, which may be some compound of diazobenzene. Probably the most vigorous high explosive at present known is the substance called hydrazoic acid or azoimide. It forms salts with metals such as AgN 3, which explode in a peculiar manner. The ammonium compound, NH 4 N 3, may become a practical explosive of great value.

Mercuric fulminate, HgC 2 N 2 O 2, is one of the most useful high explosives known. It is formed by the action of a solution of mercurous nitrate, containing some nitrous acid, on alcohol. It is a white crystalline substance almost insoluble in cold water and requiring 130 times its weight of boiling water for solution. It may be heated to 180° C. before exploding, and the explosion so brought about is much milder than that produced by percussion. It forms the principal ingredient in cap compositions, in many fuses and in detonators. In many of these compositions the fulminate is diluted by mixture with certain quantities of inert powders so that its sensitiveness to friction or percussion is just so much lowered, or slowed down, that it will fire another mixture capable of burning with a hot flame. For detonating dynamite, guncotton, &c., it is generally employed without admixture of a diluent.

Smokeless Propellants

Gunpowders and all other explosive mixtures or compounds containing metallic salts must form smoke on combustion. The solids produced by the resolution of the compounds are in an extremely finely-divided state, and on being ejected into the atmosphere become more or less attached to water vapour, which is so precipitated, and consequently adds to the smoke. The simplest examples of propellants of the smokeless class are compressed gases. Compressed air was the propellant for the Zalinski dynamite gun. Liquefied carbon dioxide has also been proposed and used to a slight extent with the same idea. It is scarcely practical, however, because when a quantity of a gas liquefied by pressure passes back again into the gaseous state, there is a great absorption of heat, and any remaining liquid, and the containing vessel, are considerably cooled. Steam guns were tried in the American Civil War in 1864; but a steam gun is not smokeless, for the steam escaping from the long tube or gun immediately condenses on expansion, forming white mist or smoke.

At the earliest stage of the development of guncotton the advantage of its smokeless combustion was fully appreciated (see Guncotton). That it did not at once take its position as the smokeless propellant, was simply due to its physical state - a fibrous porous mass - which burnt too quickly or even detonated under the pressure required in fire-arms of any kind. In the early eighties of the 19th century it was found that several substances would partly dissolve or at least gelatinize guncotton, and the moment when guncotton proper was obtained as a colloid or jelly was the real start in the matter of smokeless propellants.

Guncotton is converted into a gelatinous form by several substances, such as esters, e.g. ethyl acetate or benzoate, acetone and other ketones, and many benzene compounds, most of which are volatile liquids. On contact with the guncotton a jelly is formed which stiffens as the evaporation of the gelatinizing agent proceeds, and finally hardens when the evaporation is complete. Whilst in a stiff pasty state it may be cut, moulded or pressed into any desired shape without any danger of ignition. In fact guncotton in the colloid state may be hammered on an anvil, and, as a rule, only the portion struck will detonate or fire. Guncotton alone makes a very hard and somewhat brittle mass after treatment with the gelatinizing agent and complete drying, and small quantities of camphor, vaseline, castor oil and other substances are incorporated with the gelatinous guncotton to moderate this hard and brittle state.

All the smokeless powders, of which gelatinized guncottons or nitrated celluloses are the base, are moulded into some conveniently shaped grain, e.g. tubes, cords, rods, disks or tablets, so that the rate of burning may be controlled as desired. The Vieille powder, invented in 1887 and adopted in France for a magazine rifle, consisted of gelatinized guncotton with a little picric acid. Later a mixture of two varieties of guncotton gelatinized together was used. In addition to guncottons other explosive or non-explosive substances are contained in some of these powders. Guncotton alone in the colloid state burns very slowly if in moderate-sized pieces, and when subdivided or made into thin rods or strips it is still very mild as an explosive, partly from a chemical reason, viz. there is not sufficient oxygen in it to burn the carbon to dioxide. Many mixtures are consequently in use, and many more have been proposed, which contain some metallic salt capable of supplying oxygen, such as barium or ammonium nitrate, &c., the idea being to accelerate the rate of burning of the guncotton and if possible avoid the production of smoke.

The discovery by A. Nobel that nitroglycerin could be incorporated with collodion cotton to form blasting gelatin (see Dynamite) led more or less directly to the invention of ballistite, which differs from blasting gelatin only in the relative amounts of collodion, or soluble nitrated cotton, and nitroglycerin. Ballistite was adopted by the Italian government in 1890 as a military powder. Very many substances and mixtures have been proposed for smokeless powder, but the two substances, guncotton and nitroglycerin, have for the most part kept the field against all other combinations, and for several reasons. Nitroglycerin contains a slight excess of oxygen over that necessary to convert the whole of the carbon into carbon dioxide; it burns in a more energetic manner than guncotton; the two can be incorporated together in any proportion whilst the guncotton is in the gelatinous state; also all the liquids which gelatinize guncotton dissolve nitroglycerin, and, as these gelatinizing liquids evaporate, the nitroglycerin is left entangled in the guncotton jelly, and then shares more or less its colloidal character. In burning the nitroglycerin is protected from detonation by the gelatinous state of the guncotton, but still adds to the rate of burning and produces a higher temperature.

Desirable Qualities. - Smokelessness is one only of the desirable properties of a propellant. All the present so-called smokeless powders produce a little fume or haze, mainly due to the condensation of the steam which forms one of the combustion products. There is often also a little vapour from the substances, such as oils, mineral jelly, vaseline or other hydrocarbon added for lubrication or to render the finished material pliable, &c. The gases produced should neither be very poisonous nor exert a corrosive action on metals, &c. The powder itself should have good keeping qualities, that is, not be liable to chemical changes within ordinary ranges of temperature or in different climates when stored for a few years. In these powders slight chemical changes are generally followed by noticeable ballistic changes. All the smokeless powders of the present day produce some oxide of nitrogen, traces of which hang about the gun after firing and change rapidly into nitrous and nitric acids. Nitrous acid is particularly objectionable in connexion with metals, as it acts as a carrier of oxygen. The fouling from modern smokeless powders is a slight deposit of acid grease, and the remedy consists in washing out the bore of the piece with an alkaline liquid. The castor oil, mineral jelly or camphor, and similar substances added to smokeless powders are supposed to act as lubricants to some extent. They are not as effective in this respect as mineral salts, and the rifling of both small-arms and ordnance using smokeless powders is severely gripped by the metal of the projectile. The alkaline fouling produced by the black and brown powders acted as a preventive of rusting to some extent, as well as a lubricant in the bore.

Danger in Manufacture

In the case of the old gunpowders, the most dangerous manufacturing operation was incorporation. With the modern colloid propellants the most dangerous operations are the chemical processes in the preparation of nitroglycerin, the drying of guncotton, &c. After once the gelatinizing solvent has been added, all the mechanical operations can be conducted, practically, with perfect safety. This statement appears to be correct for all kinds of nitrated cellulose powders, whether mixed with nitroglycerin or other substances. Should they become ignited, which is possible by a rise of temperature (to say 180°) or contact with a flame, the mixture burns quickly, but does not detonate.

As a rule naval and military smokeless powders are shaped into flakes, cubes, cords or cylinders, with or without longitudinal perforations. All the modifications in shape and size are intended to regulate the rate of burning. Sporting powders are often coloured for trade distinction. Some powders are blackleaded by glazing with pure graphite, as is done with black powders. One object of this glazing is to prevent the grains or pieces becoming joined by pressure; for rods or pieces of some smokeless powders might possibly unite under considerable pressure, producing larger pieces and thus altering the rate of burning. Most smokeless powders are fairly insensitive to shock. All these gelatinized powders are a little less easily ignited than black powders. A slightly different cap composition is required for small-arm cartridges, and cannon cartridges generally require a small primer or starter of powdered black gunpowder.

It is desired that a propellant shall produce the maximum velocity with the minimum pressure. The pressure should start gently so that the inertia of the projectile is overcome without any undue local strain on the breech near the powder chamber, and more especially that as more and more space is given to the gases by the movement of the projectile up the gun to the muzzle, gas should be produced with sufficient rapidity to keep the pressure nearly uniform or slightly increasing along the bore. The leading idea for improvements in relation to propellants is to obtain the greatest possible pressure regularly developed, and at the same time the lowest temperatures. (W. R. E. H.) Law. - In 1860 an act was passed in England "to amend the law concerning the making, keeping and carriage of gunpowder and compositions of an explosive nature, and concerning the manufacture and use of fireworks" (23 & 24 Vict. c. 139), whereby previous acts on the same subject were repealed, and minute and stringent regulations introduced. Amending acts were passed in 1861 and 1862. In 1875 was passed the Explosives Act (38 & 39 Vict. c. 17), which repealed the former acts, and dealt with the whole subject in a more comprehensive manner. This act, containing 122 sections, and applying to Scotland and Ireland, as well as to England, constitutes, with various orders in council and home office orders, a complete code. The act of 1875 was based on the report of a committee of the House of Commons, public opinion having been greatly excited on the subject by a terrible explosion on the Regent's Canal in 187 4. Explosives are thus defined: (i) Gunpowder, nitroglycerin, dynamite, gun-cotton, blasting powders, fulminate of mercury or of other metals, coloured fires, and every other substance, whether similar to those above-mentioned or not, used or manufactured with a view to produce a practical effect by explosion or a pyrotechnic effect, and including (2) fog-signals, fireworks, fuses, rockets, percussion caps, detonators, cartridges, ammunition of all descriptions, and every adaptation or preparation of an explosive as above defined. Part i. deals with gunpowder, providing that it shall be manufactured only at factories lawfully existing or licensed under the act; that it shall be kept (except for private use) only in existing or new magazines or stores, or in registered premises, licensed under the act. Private persons may keep gunpowder for their own use to the amount of thirty pounds. The act also prescribes rules for the proper keeping of gunpowder on registered premises. Part ii. deals with nitro-glycerin and other explosives; part iii. with inspection, accidents, search, &c.; part iv. contains various supplementary provisions. By order in council the term "explosive" may be extended to any substance which appears to be specially dangerous to life or property by reason of its explosive properties, or to any process liable to explosion in the manufacture thereof, and the provisions of the act then extend to such substance just as if it were included in the term "explosive" in the act. The act lays down minute and stringent regulations for the sale of gunpowder, restricting the sale thereof in public thoroughfares or places, or to any child apparently under the age of thirteen; requiring the sale of gunpowder to be in closed packages labelled; it also lays down general rules for conveyance, &c. The act also gives power by order in council to define, from time to time, the composition, quality and character of any explosive, and to classify explosives, and such orders in council are frequently made including new substances; those in force will be found in the Statutory Rules and Orders, tit. "explosive substance." The Merchant Shipping Act 1894 imposes restrictions on the carriage of dangerous goods in a British or foreign vessel, "dangerous goods" meaning aquafortis, vitriol, naphtha, benzine, gunpowder, lucifer matches, nitro-glycerin, petroleum and any explosive within the meaning of the Explosives Act 1875. The act is administered by the home office, and an annual report is published containing the proceedings of the inspectors of explosives and an account of the working of the act. Each annual report gives a list of explosives at the time authorized for manufacture or importation, and appendices containing information as to accidents, experiments, &c.

Practically every European country has legislated on the lines of the English act of 1875, Austria taking the lead, in 1877, with an explosives ordinance almost identical with the English act. The United States and the various English colonies also have explosives acts regulating the manufacture, storage and importation of explosives. (See also Petroleum.) (T. A. I.) Bibliography.-M. Berthelot, Sur la force des matieres explosives (Paris, 1883); P. F. Chalon, Les Explosifs modernes (Paris, 1886); W. H. Wardell, Handbook of Gunpowder and Guncotton (London, 1888); J. P. Cundill, A Dictionary of Explosives (London, 1889 and 1897); M. Eissler, A Handbook of Modern Explosives (London, 1896, new ed. 1903); J. A. Longridge, Smokeless Powder and its Influence on Gun Construction (London, 1890); C. Napier Hake and W. Macnab, Explosives and their Power (London, 1892); G. Coralys, Les Explosifs (Paris, 1893); A. Ponteaux, La Poudre sans fumee et les poudres anciennes (Paris, 1893); F. Salvati, Vocabolario di polveri ed explosivi (Rome, 1893); C. Guttmann, The Manufacture of Explosives (London, 1895 and later); S. J. von Romocki, Geschichte der Sprengstoffchemie, der Sprengtechnik and des Torpedowesens bis zum Beginn der neusten Zeit (Berlin, 1895); Geschichte der Explosivstoffe, die rauchschwachen Pulver (Berlin, 1896); P. G. Sanford, Nitro-explosives (London, 1896); L. Gody, Traite theorique et pratique des matieres explosives (Namur, 1896); R. Wille, Der Plastomerite (Berlin, 1898); E. Sarrau, Introduction la theorie des explosifs (1893); The'orie des explosifs (1896); O. Guttmann, Manufacture of Explosives (London, 1895); E. M. Weaver, Notes on Military Explosives (New York, 1906); M. Eissler, The Modern High Explosives (New York, 1906); Treatise on Service Explosives, published by order of the secretary of state for war (London, 1907). Most of the literature on modern explosives, e.g. dynamite, &c., is to be found in papers contributed to scientific journals and societies. An index to those which have appeared in the Journal of the Society of Chemical Industry is to be found in the decennial index (1908) compiled by F. W. Renant.


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