MM. Bottée and Riffault (Traité de l'art de Fabriqué la poudre à canon, p. 197,) after making some observations on the constitution of powder, and the action which takes place when it is burnt, with the aeriform products that result, give some remarks on the proportion of charcoal necessary to decompose a given quantity of nitric acid; and conclude generally, that in the production of carbonic acid gas, the principal gas which is formed, while the nitric acid is decomposed, and gives up its oxygen to the carbon, the azote is liberated in the state of gas, and at the same time caloric is evolved. They observe then, that the ancient formula for the manufacture of gunpowder, as used in France, consists of the following proportions, viz: 0.750 saltpetre, 0.125 charcoal, and 0.125 sulphur, which agrees with modern experiments, although chemistry at that period was in its infancy. M. Pelletier, a member of the National Institute, and M. Riffault made several experiments at Essonne, on different proportions of nitre, charcoal, and sulphur in the fabrication of powder. It is unnecessary to state the different proportions, made use of, or the experiments on the strength of the powder made with the eprouvette. They observe, however, that powder made in the following proportions, was more satisfactory, viz. 0.76 saltpetre, 0.15 charcoal, 0.09 sulphur, and 0.76 saltpetre, 0.14 charcoal, and 0.10 sulphur.
Before we give the gaseous products, according to these gentlemen, it will be necessary to observe, that the quantity of nitric acid in nitrate of potassa, is 48.62 in the hundred, and according to Gay-Lussac, nitric acid is composed in volume of 250 oxygen and 100 azote, or in weight of 69.488 oxygen, and 30.512 azote.
Using the French gramme in the present instance, it appears that 75 grammes of nitrate of potassa, the proportion of this salt which enters into 100 grammes of gunpowder for war, contains 36.47 grammes of nitric acid; and that this quantity of acid is formed of 25.34 grammes of oxygen, and 11.13 grammes of azote. That quantity of oxygen (25.34) is disengaged from its combination with azote in the nitric acid, at the instant of the inflammation of the powder by the charcoal, forming carbonic acid; the constituents of which, according to the proportions established by Gay-Lussac and others, must be in the ratio of 27.376 of carbon and 72.624 of oxygen. If 25.34 grammes of oxygen exist in 75 grammes of nitrate of potassa, the proportion usually admitted, then it will require 9.55 grammes of carbon to saturate it, so as to produce carbonic acid. It is necessary to consider, that this is independent of any foreign earthy or saline matter or moisture which may exist.
With respect to the presence of hydrogen in charcoal, the observations of Dr. Priestley, Cruikshanks, Kirwan, Berthollet, Gay-Lussac, Thenard, Vauquelin, Lowitz and some others, are conclusive on that head. Lavoisier made the quantity of hydrogen in charcoal upon an average, to be 0.125 of its weight. See Memoirs de la Société d'Arcueil, tome ii, p. 343, and the Statique Chimique, tome ii, pages 44 and 45, and also charcoal in a preceding section.
It is said, that by employing more charcoal than is necessary to decompose the nitric acid of the nitre, the excess passes off, not as carbonic acid, but carbonic oxide, or gaseous oxide of carbon, which is necessarily inflamed, and finally forms carbonic acid, as one of the products with the carbonic acid originally formed. But the carbonic oxide, to be changed into carbonic acid, requires in fact the oxygen of the atmosphere.
If 34.89 grammes of carbonic acid result from the combustion of 9.55 grammes of carbon, it must unite with a quantity of oxygen, as before expressed, and according to the temperature, be more or less expanded. The 11.13 grammes of azote thus disengaged from its combination with oxygen, in the nitric acid, remains, of course, in the gaseous state, and is also expanded by caloric. The quantity of the latter is stated by Lavoisier, to be 430 degrees, using a scale of 80 parts; and according to more recent experiments, it is fixed at 600 degrees of the centigrade thermometer. The experiments of Gay-Lussac are more recent, in which he has given the dilatation of the gases, and the quantity of free caloric evolved, which corresponds with the last data. We have not room to insert his remarks.
The use of sulphur with the charcoal, in the fabrication of powder, Bottée and Riffault state to be, (page 204) that it inflames more rapidly than charcoal, and at a lower temperature, which accelerates the combustion of the charcoal, and consequently the detonation of the powder. The presence of the sulphur augments the volume of gas, by producing sulphurous acid gas. The proportion of sulphur in the powder for war, is, 0.125, for musket powder, 0.10, and for mining powder, 0.20, according to the same gentlemen.
M. Fourcroy (Système des Connaissances Chimiques, tome iii, p. 122.) among other products of the combustion of powder, mentions ammonia. If ammoniacal gas be formed, the hydrogen must proceed from decomposed water, and the azote from the nitric acid. Prussine, cyanogen, or carburet of nitrogen, the radical of prussic acid, may also be generated by the union of carbon and nitrogen or azote, in the same manner. We know that cyanogen may exist in the form of gas; but as it is inflammable, burning with a bluish flame mixed with purple, we may infer, nevertheless, that, if generated, it must undergo decomposition by the process of combustion. Although I know of no experiments on this subject, either by Gay-Lussac, Vauquelin or Davy, all of whom have investigated the properties of this compound of carbon and azote, which Dr. Ure has called prussine; yet it would appear, that during its combustion, the carbon is changed into carbonic acid, and whether the azote be also combined with oxygen, or merely set at liberty, is altogether uncertain. Many difficulties present themselves to a complete and satisfactory set of experiments on the gaseous products of fired gunpowder.
With respect to the granulation of powder, we may observe, that although some writers consider that granulated powder is stronger than the fine powder, yet others are of opinion, that its strength is not increased by granulation. Grained powder is more fit for use; but the graining of it prevents the whole of the powder from taking fire instantaneously. Gunpowder, although prepared in the best manner, is not wholly consumed by inflammation. However remarkable it may appear, yet nevertheless it is true, that a considerable portion of gunpowder fired in a confined space is thrown out without being kindled. That gunpowder passes through a volume of fire without being consumed, may seem incredible, yet the fact may be proved by firing with a musket upon snow, or upon a paper screen.