We have to lament that these experiments were not made with more precision. The gases generated were considered by Mr Robins as common air, the specific gravity of which is 1. These gases, however, being a mixture of carbonic acid, carbonic oxide, and azotic gases, should have been taken at a mean not less than 1.25. There is also some uncertainty about the allowance made for the heat of the receiver ; and the volume was not increased by that circumstance so much as 5th of the whole, which he supposes to be the case. The very little which was known of gaseous chemistry at the time Mr Robins made his experiments, does not admit of our wondering that no more was established by his labours. The constituents of nitre were then little known ; and therefore the nature of the gases resulting from the decomposition of gun powder could not be ascertained. He was satisfied with calling the gaseous product air, and supposed it to have only the properties of common air. In order to apply the chemical facts at present known to explain the nature of gunpowder, we shall compare the proportions of the ingredients used by different manufacturers with those proportions which theory could point out, in order to pro duce a maximum effect.
An intelligent account of making gunpowder has been given by Mr Coleman, of the royal gunpowder mills at Waltham Abbey. (Phil. Mag.. vol. ix.) In some obser vations at the end of the paper, Mr. Coleman has taken a very proper view of the theory of gunpowder, by giv ing some calculations relative to the resulting products. He has taken into the account the water, which he rates at 4 per cent. It has not been ascertained, that water undergoes any change in the decomposition of gunpow der ; nor, indeed, is it very probable that any such effect takes place. He has also given too little oxygen for sulphurous acid. He states it to be 30 per cent, when it is actually 50. It appears from experiments made in the firing of gunpowder, that very little of the sulphur enters into combination with the oxygen, and we believe not after the carbon is kindled. The residuum is always very near a complete sulphuret of potash ; and the quan tity of sulphur used in the composition is seldom more than is just sufficient to form the sulphuret. This is rendered highly probable, from the fact of gunpowder possessing the same strength with very different propor tions of sulphur. Indeed, M. Chaptal has made very good gunpowder without sulphur. It is however different, in a mechanical point of view, and on that account would not answer in practice. It is therefore highly probable, that the sulphur does not form sulphurous acid when the explosion takes place, since oxygen seems to unite with the carbon alone. The potash, when deserted by oxygen and the nitrogen, assumes the form of a fine dust of powder, and the sulphur the form of vapour. These
combine,• forming a sulphuret or potash, which appears in white fumes, and adheres to surrounding bodies. The moment this white efflorescence is touched with the tongue, the exact taste of sulphuret of potash is per ceived. If the carbon were very defective in quantity, and the sulphur in the usual proportion, some sulphu rous acid would doubtless be formed, and the smell of it would be very perceptible in the fumes resulting from its decomposition ; but no smell of this kind is per ceived in the explosion of ordinary gunpowder.
The following Table contains some of the proportions used by different manufacturers in this and other coun tries.
Doubtless all these varieties are very good powder, which would not have been the case, had the charcoal been as uncertain in its proportions as the sulphur.
It will be admitted on all hands, that the best gunpow der must result from such materials as explode the quick est, leaving the least possible residuum, and affording the greatest possible volume of elastic fluid. Now, if sulphur did, by its combination with oxygen, form an elastic fluid, the resulting gas, which is sulphurous acid, is nearly 1.5 times heavier than carbonic acid, and therefore contributes less force in a given weight. It will be found, when nitre is deflagrated with charcoal, that carbonic oxide is formed as well as carbonic acid, which contributes more elastic force than the same weight of carbonic acid.
There is one good reason to be given for the use of the sulphur, although it does not contribute to the produc tion of any elastic fluid. The carbonic acid which is generated would doubtless combine with the potash, if it were not for the presence of the sulphur ; and thus so much elastic fluid would be lost. That this is the case, we know from the fact, that carbonate of potash is always formed when nitre is decomposed by charcoal alone. This would be the case to a certain extent with gunpow der made without sulphur ; some carbonate of potash would be formed.
It will appear, from these facts and observations, that the propositions for gunpowder will be those in which the carbon will just consume the oxygen of the nitre, and the sulphur as much as will exactly saturate the potash. This will be effected by' an atom each of nitre and sul phur, and three atoms of carbon, or nitre 95.5 ; charcoal 16.'; ; and sulphur 15. These will give in the 100 nitre 75.4 ; of charcoal 11.8 ; and sulphur 12.8. These pro portions agree with the best in practice. The bodies which result from the decompositions of this compound, will be in 126.7 parts, 60 of sulphuret potash ; 40 8 of carbonic acid ; 12.9 of carbonic oxide ; and 13 of azot.