A System of Pyrotechny / Comprehending the theory and practice, with the application of chemistry; designed for exhibition and for war.

by James Cutbush

The effect, therefore, that results from the inflammation of fire-works, in which iron or steel forms a constituent part, is nothing more than a vivid combustion of the metal; and during that process it becomes oxidized, as it does not form an acid with oxygen, like arsenic, antimony, and some other metals.

The combustion of iron or steel may be shown by a very brilliant experiment, that of burning it in oxygen gas. A steel wire, harpsichord wire for instance, formed into a spiral, with a small piece of wood dipped in sulphur, stuck on its end and then set on fire, upon being immediately introduced into a bottle, containing pure oxygen gas, will burn with great brilliancy, emitting a number of sparks or scintillations, which fall like rain. In making the experiment, some sand should be put into the bottle to prevent the sparks from breaking it. This experiment illustrates the rapid combustion of iron, or steel. For the oxygen gas supports the combustion; and while the oxygen is actually taken up by the metal, which becomes oxidized, and therefore increased in weight, in the same manner as it does when inflamed in fire-works, the caloric, the other constituent of oxygen gas, is given out in a free state, and, with the light at the same time evolved, produces the phenomena of combustion.

Many other experiments might be mentioned, in which the same effects take place, and from which the same conclusions may be drawn. But with respect to the effect, whether it be dull, brilliant, or very brilliant, depends more on the quality of the metal, than perhaps, on its subsequent mixture with the other materials. Crude iron, usually called cast iron, seems to possess this property in an eminent degree; but in the experiment with oxygen gas, steel is always preferable, as the combustion is more rapid, and the effect more striking. The difference, which we will not attempt to explain, may depend on the state, as well as the proportion of carbon, which enters into crude iron, as well as steel. In one case, the combustion ensues in contact with nitre, and in atmospheric air; in the other, in contact only with oxygen gas. Be this as it may, this inference is conclusive, that, in all cases of the combustion of iron in fire-works, the metal itself unites with oxygen, and the result of the combustion is an oxide of iron; and with respect to the carbon, in both instances, it is converted alike into carbonic acid. So that whether the iron receives its oxygen from the nitre, or from the air, or from both, is immaterial, as the products are the same.

When iron is exposed to the atmosphere, it tarnishes, and is gradually changed into a brown or yellow powder, called rust. This change is owing to its combination with oxygen; and its affinity for oxygen is such, that, when the vapour of water is made to pass through an ignited gun-barrel, it is decomposed, the metal becoming oxidized, and the hydrogen, the other constituent of the water, being liberated in the form of gas.

Gun barrels are browned by a process of oxidizement. There are several processes recommended. One of which is, to rub the barrel over with diluted nitric or muriatic acid, and then, to lay it by for a week or two, until a complete coat of rust is formed. A brush, made of iron wire, is then applied; afterwards, oil and wax, and the barrel is finished by rubbing it with a cloth. The gunsmiths in Philadelphia use a mixed solution of sulphate of copper, tincture of the muriate of iron, and sweet spirit of nitre. This they apply by means of a cloth. The object is to form a rust, and to render it permanent on the barrel by hard friction along with wax. When sulphate of copper is employed, metallic copper is precipitated on the barrel. A coat of rust, put on in this manner, prevents effectually the oxidizement of the iron; and in point of utility, and the saving of labour in polishing and keeping muskets in order, the browning of barrels is certainly advantageous in the land service. At sea, in particular, where iron is more readily oxidized, this plan ought always to be adopted. With regard to the use of dragon's blood, it is entirely too temporary in its effect to be depended on. I was informed by an intelligent gunsmith, who followed the practice of browning barrels in Europe, that he has known the browning to remain very perfect for years, and that the best mode of insuring its durability is to use the steel brush, which carries in, as he expressed it, the rust.

The oxides, which are formed by the union of oxygen with iron, are two; namely, the black and the red; the first being the protoxide, and the last the peroxide. The black oxide, which is formed by the combustion of iron, and by other processes, contains 56 iron + 16 oxygen. The common rust of iron is the peroxide of this metal, combined with carbonic acid. It may be formed by exposing the protosulphate of iron, or green vitriol, in solution, to the atmosphere, and then adding an alkali. This oxide contains more oxygen than the preceding; it consisting of 56 iron + 24 oxygen.

The tempering of cutting instruments, an operation which requires great delicacy and exactness, after that of hardening, is intended to obtain a fine and durable edge; and as this subject may be interesting in a military point of view, we deem the following remarks of use.

The hardening of steel instruments is performed by heating them to a cherry-red, and then immersing them in cold water. The tempering is another process, calculated, as we observed, to obtain a fine and durable edge. This is performed by heating oil to a certain temperature, and plunging the instrument into it, where it remains until the colour appears, indicative of the particular kind of temper which is intended to be given. The experiments of Stoddart, (Nicholson's Quarto Journal, iv, 129,) are conclusive on this subject; for his experiments prove, that, between 430° and 450° the instrument assumes a pale yellowish tinge: at 460° the colour is a straw-yellow, and the instrument has the usual temper of pen-knives, razors, and other fine edge tools. The colour gradually deepens as the temperature rises, and at 500° becomes a bright brownish metallic yellow. As the heat increases, the surface is successively yellow, brown, red, and purple, to 580°, when it becomes of a uniform deep blue, like that of watch springs. Before the instrument becomes red-hot, the blue changes to a water colour, which is the last distinguishable colour. These different shades are owing to the oxidizement of the surface of the metal; and the art of ornamenting sword-blades, knives, &c. long practised in Sheffield, depends on this principle. The general process is, that an oily composition is used, with which flowers and various ornaments are painted. On the application of the heat required for tempering it, that part which was covered with the composition, is not altered, whereas, the uncovered parts of the blade are changed. These ornaments, when the paint is removed, have the natural colour of polished steel. When steel is heated in hydrogen gas, no appearance of the kind takes place, a fact which shows, that it is owing to the oxidizement of the metal.

Iron is soluble in the acids. By the assistance of water, it is acted upon by sulphuric acid; the metal being oxidized, and the oxide dissolved, while hydrogen gas is evolved. The salt, formed in this case, is the sulphate of iron, green vitriol, or copperas. With muriatic, nitric, acetic and other acids, it forms various salts; and with gallic acid, when the iron is peroxidized, it forms the pergallate of iron, or common writing ink, and also the bases of black dye.