Pyrotechny is defined the doctrine of artificial fire-works, whether for war or exhibition, and is derived from the Greek, πυρ fire, and τεχνη art. In a more general sense, it comprehends the structure and use of fire-arms, and the science which teaches the management and application of fire in several operations.
Sec. II. General theory of Pyrotechny.
In the composition of artificial fire, various substances are employed, having different properties, and designed to produce certain effects characterised by particular phenomena. These substances are either inflammable, or support the combustion of inflammable bodies. As pyrotechnical mixtures are differently formed, and of various substances, the effects are also modified, although combustion, under some shape always takes place.
Combustion is either modified, retarded, or accelerated; and in consequence of the presence of certain substances, different appearances are given to flame.
The conditions necessary for combustion are, the presence of a combustible substance, of a supporter of combustion, and a certain temperature. Thus, charcoal when raised to the temperature of 800° in the open air, takes fire. This elevation of temperature enables it to act chemically on the oxygen gas of the atmosphere; the latter, as it comes in contact, being decomposed. Now, as oxygen gas is a combination of oxygen and caloric, the caloric being in a latent state, the charcoal unites with the oxygen, and the phenomena of combustion ensue; that is, an evolution of heat and light. The caloric of the decomposed gas is given out in a free state, and, according to the theory of Dr. Thomson, (Thomson's System of Chemistry, vol. i.) the light proceeds from the burning body. We have then an instance of combustion, in which there is a combustible, a supporter of combustion, and an elevated temperature. The old theory of combustion, called the Stahlian theory, which presupposes an element called phlogiston, or a principle of fire, to exist in all bodies under some modification, would explain these effects by merely supposing, that combustion was nothing more than a disengagement of phlogiston; and that when a body had lost its inflammable principle, (as a metal, when oxidized), it became dephlogisticated. But, as it proved that phlogiston is a hypothetical element, and the anti-phlogistic doctrine clearly shows, that combustion is no other than a process which unites the supporter with the combustible, forming new products; it follows, that, in all changes of the kind, the same reasoning will apply, and the same principle be tenable.
The products of combustion depend on the nature of the substance burnt, and the supporter employed. Thus, in the instance just mentioned, the charcoal, by its union with oxygen, is changed into carbonic acid, which takes the gaseous state. We say then, that carbonic acid is the product of the combustion of charcoal, or, chemically speaking, of carbon. As resins, oil, &c. contain hydrogen, as well as carbon, the products in such cases would be water, as well as carbonic acid.
The chemical effects, therefore, which we consider in fire-works, forming the basis on which a theory of sundry phenomena may be formed, are no other than the result of the action of one body on another, according to the laws which govern such action, and the consequent operation of chemical combination. Combustion, in fire-works, may be considered a primary agent in all effects which characterise artificial fire.
The second change, with respect to the appearance of the flame, the formation of stars, serpents, rain, &c. terms used in the art, is owing either to new chemical changes which the substances undergo, or to the decomposition of the products themselves. These effects, it is obvious, must be governed by the circumstances, under which the mixtures are made. Saltpetre, for instance, is the basis of fire-works, whether used in a separate state, or employed in mixture with charcoal and sulphur, as in gun-powder; and, from its composition, is adapted to all the purposes of the art, because it yields its oxygen very readily to all inflammable bodies. In consequence of the decomposition, it undergoes at an elevated temperature, when brought in contact with charcoal, sulphur, &c. and various substances which contain carbon, as pitch, rosin, turpentine, tallow, copal, and amber, combustion results, and, according to circumstances, is more or less rapid, and the flame also more or less brilliant.
When charcoal, in the state of ignition, is brought in contact with nitre, a deflagration takes place, because, at the temperature of ignition, it has the property of decomposing the nitric acid of the nitre; and as this process unites the carbon with the oxygen, in the proportion necessary to constitute carbonic acid, this acid is accordingly produced. When, therefore, we inflame a mixture of nitre, charcoal, and sulphur, or gun-powder, the whole or greater part disappears; and if we were to collect in a pneumatic apparatus, the products of the combustion, it would be found, that they are nearly altogether gaseous, and composed, as we shall speak hereafter, of sundry elastic aëriform fluids. This decomposition, the immediate effect of the charcoal on the nitric acid of the nitre, is the same as in the preceding instance, for carbonic acid gas is formed in both cases. We have then another instance of combustion, where a number of substances are concerned, and therefore, the products must be numerous.
We notice this subject more particularly, since, as in the different fire-works, nitre and inflammable bodies are used in different proportions, the result is always affected by the same laws of chemical decomposition; for the same substances, placed under similar circumstances of proportion, mixture, &c. afford the like results. If carbon alone be employed, carbonic acid gas is the result; if oil, tallow, rosin, or turpentine be used, we have then, as we had occasion to remark, water, as well as carbonic acid, by reason of the union of the hydrogen, which forms one of their constituent parts, with a part of the oxygen of the nitric acid.