140 OUR PHYSICAL WORLD 



gunpowder set off in the open does not explode but merely burns 

 rapidly. If, however, this same gunpowder is put in a confined 

 space as it is when rammed down in the gun barrel and then 

 touched off, the gases formed need to occupy so much more space 

 than the solids that the elastic force exerted is very great. The 

 bullet, therefore, is hurled out of the gun barrel with great speed. 

 If the powder is confined in a hole bored in rock and then 

 touched off the expansive force of the gases is so great it bursts 

 the rock. 



The first crude gun was rapidly improved. The metal tube 

 or barrel was fitted to a stock that was shaped so as to rest 

 against the shoulder, enabling one to aim the piece and lessening 

 also the effect of the recoil. In some of these early guns a small, 

 toothed, steel wheel, bearing upon a piece of flint or pyrite, was 

 rotated rapidly by a little crank, so furnishing the spark that 

 set off the powder in the pan. Later a hammer carrying a piece 

 of flint struck a piece of steel so producing the spark (Fig. 55). 

 The flintlock musket was the arm of the British army until 

 1844. Most of these old guns were loaded from the muzzle. 

 The charge of powder, as also the ball, was held in place by 

 wadding and was rammed down with the ramrod. 



The next improvement of prime importance was the substitu- 

 tion of a percussion cap for the flint and steel. The hammer 

 struck the cap which was set on a hollow post over the powder 

 charge. The cap, a small, cup-shaped metal affair, contained a 

 substance that when struck with the hammer exploded and drove 

 a flame down to ignite the powder. This improvement was used 

 on sporting guns for some time before it was used on the guns 

 furnished the armies, for it was an expensive proposition to 

 change the type of gun for an entire army. 



Next came the breech-loading gun. The breechloader was 

 devised long before it came into general use, in fact there were 

 breech-loading guns made back in the fifteenth century, but it 

 was always a difficult matter to make the breech so tight that 

 the explosion would not blow it out. When this was finally 



