gunpowder: its manufacture and conveyance. 
43 
rating sound-waves in the air. When the explosion occurs in a 
confined space, the weakest portion of the confining bodies gives 
way before it. In quarrying, the rocks are rent, as the gas from 
the blasting-powder forces them apart. In blowing down walls 
and gates, the mass of earth heaped on one side to form the 
“tamping” offers a greater resistauce than the wood or stone 
on the other, and the wall or gate gives way. In firing a 
cannon, the loose shot offers less resistance than the solid coils 
of the gun, and it is driven out to a distance proportioned to 
the force of the charge. If there is any defect impairing the 
strength of the cannon, or if the shot wedges in the bore, the 
gun bursts ; for nothing we know of can resist the force of the 
gas. Eecent experiments prove that this force, exerted in 
closed vessels unrelieved by expansion, is equal to a pressure of 
about forty tons on the square inch. 
Of the three materials of which gunpowder consists — sulphur, 
charcoal, and saltpetre — only the two last are, strictly speaking, 
essential to it. The gas is actually generated from tire charcoal 
and saltpetre, therefore a mixture of these only will explode. 
On ignition the charcoal decomposes the saltpetre, its combus- 
tion being supported by the oxygen of the latter, in combination 
with which it forms carbonic acid gas, and this, mixed with the 
nitrogen from the saltpetre, is the gas which produces the useful 
effect. But when gunpowder is thus made with saltpetre and 
charcoal onty, the power developed by the explosion is com- 
paratively trifling, and sulphur has to be added to increase it to 
such an extent as to make it really efficient. The sulphur acts 
in two ways to this end. In the first place, it ignites at a lower 
temperature than either charcoal or saltpetre, and its combustion 
accelerates both the decomposition of the saltpetre and the gene- 
ration of gas, by combining with the potassium of the saltpetre 
and liberating the oxygen. Then, by heating the carbonic acid 
and nitrogen, it considerably increases their volume, and, con- 
sequently, their explosive force. The flash, and smoke, and the 
fouling of the gun, are the result of the decomposition of the 
saltpetre, and consist of sulphates and carbonates of potassa, 
resulting from the combination of potassium with the sulphur 
and carbon. The substances thus formed, swept out into the 
air, become flame and smoke, or remain in the bore of the gun 
as fouling, and it is these solid substances that blacken the faces 
of men engaged in close conflict. 
Thus we see that of the materials of gunpowder saltpetre is 
the most important. Both saltpetre and sulphur arrive in 
England in a rough state, mixed with various impurities. It is 
generally the practice in private factories to purchase these 
materials after they have been refined elsewhere ; but at Wal- 
tham the refining process is carried on within the works. By 
