As the brilliancy of the sparks, produced by the iron and steel dust, is a desideratum in the formation of some fire-works, and as this brilliancy depends upon the nature and quality of the metal, it may not be improper to offer some remarks on these subjects. That iron, when finely divided is capable of producing sparks of fire, is a well known fact; and we see it daily in the operations of the smith, when ignited iron is hammered on the anvil. The scintillation produced by the steel, when struck with a flint, is of the same character. In the latter case, the metal is actually fused, and, when caught on a paper, and examined with a microscope, will appear globular, and partly oxidized. Hence it is, that gunpowder is inflamed by this spark, which is nothing more than highly ignited, and inflamed iron, possessing a temperature more than sufficient to inflame gunpowder. 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.