The extraction of saltpetre from the earth, (principally nitrate of lime), by using a lixivium of wood-ashes; the formation of rough, and subsequently of refined nitre; the various methods of refining saltpetre, and particularly that adopted in France; with sundry facts respecting the origin of nitre, and on the formation of artificial nitre beds; all claim our particular notice. The extraction of sulphur from its combinations, and the means used for purifying it for the purpose of gunpowder, are also considered in the same manner. The subject of charcoal, an essential constituent of gunpowder, claims, in like manner, particular attention. The various modes of charring, the woods employed, the quantity of coal obtained, the formation of pyroacetic acid in the process of carbonization, and many facts of the same kind are considered. These subjects, _viz._ nitre, charcoal, and sulphur, are highly important to the manufacturer of gunpowder. A knowledge of the various processes for refining saltpetre; the best and most approved modes of carbonizing wood; the purification and quality of sulphur; the different processes for making gunpowder, with the proportion of the ingredients used in France and elsewhere; the granulation, glazing, and drying of powder, the use of the steam apparatus, and the different modes of proving it, and of examining it chemically; and the means of ascertaining the purity of nitre in any specimen of gunpowder; are, with others, subjects of particular interest to the gunpowder manufacturer. With respect to the Theory of the explosion of gunpowder, we have noticed it at some length, and have added the experiments and observations of Mr. Robins, and of other persons, made at different periods. In the consideration of the gaseous products, and the caloric evolved by the combustion of powder, we have taken a view of the gases produced, the cause of their production, the dilatation which they suffer, and the experiments of Lavoisier and Laplace, with regard to latent heat, and deducing therefrom some views of the probable cause of the production of caloric in fired gunpowder.[7] Our observations respecting rockets, the theory of their ascension, of the Congreve carcass and Asiatic rockets, and some others, are we apprehend sufficiently extensive. As it regards the different incendiary compositions, and their use in war, the reader will find ample instructions on these heads.