Charcoal 15 Saltpetre 75 Sulphur 10 --- 100 ---
With these proportions, the carbon should be burned to carbonic acid, and the sulphur should be all taken up by the potassium. Powder of this composition is used for fire-arms. For blasting purposes, as before remarked, the proportion of sulphur is increased at the expense of the saltpetre, in order to quicken combustion and to lessen the cost, to 20 per cent. as a maximum. With such proportions, some of the carbon is burned to carbonic oxide only, and some of the sulphur goes to form sulphurous acid, gases that are particularly noisome to the miner.
It is essential to the regular burning of the mixture that the ingredients be finely pulverized and intimately mixed. The manufacture of gunpowder consists of operations for bringing about these results. The several substances are broken up by mechanical means, and reduced to an impalpable powder. These are then mixed in a revolving drum, and afterwards kneaded into a paste by the addition of a small quantity of water. This paste is subjected to pressure, dried, broken up, and granulated; thus, the mixing being effected by mechanical means, the compound is called a mechanical mixture. It will be observed that in a mechanical mixture the several ingredients are merely in contact, and are not chemically united. They may therefore be separated if need be, or the proportions may be altered in any degree. Mechanical mixtures, provided the bodies in contact have no chemical action one upon another, are stable, that is, they are not liable, being made up of simple bodies, to decompose spontaneously.