Page:Popular Science Monthly Volume 91.djvu/377

 What a Match Is to Your Cigar

So is a primer to its giant shell

��NOWADAYS every one knows what a shell looks like, and some of us can even differentiate between a high-explosive shell and a shrapnel. We are quite familiar with shells of small caliber and read constantly of the destructiveness of the large 15- inch and 16-inch shells. There is nothing novel to us in the general appearance of a shell such as shown here. We know that in the base of that shell is a little disk which corresponds with the cap in the cartridge-case of our own shot-gun. This is the primer, and while its existence is taken for granted, its mechanism and ~

operation are less copper. s^

���It is the primer which ignites the charge in the cartridge case to drive the pro- jectile from the gun on its mission of destruction. Its function is similar to that of the cap in the base of a shot-gun cartridge, but the duties devolving upon the primer of an artillery shell are more complex. The primer has not only to fire the powder charge in the cartridge case, but also to prevent any of the propelling gases from escaping back into the breech of the gun.

The primer is composed of six parts — not including the explo- sives used — each one of which has a distinct and definite duty to perform. First, there is the primer body, which houses the operating mechanism and mediums and which screws into the base of the cartridge case. In what may be termed the primer "hub," there is the primer cap which corre- sponds with the cap of a shot-gun cartridge. Next comes the anvil against which the explosive cap has to be driven to ignite the charge. Capping the central hole

���Above: Cra- ter made by giant shell

��of the hub and hold- ing the anvil in place is a tight-fitting plug with several flash holes. Completing the primer is the closing-in disk over which the edges of the primer body are rivet- ed. Within the conical cavity in the anvil base is a small soft brass ball which plays an important and interesting part. A highly explosive and ignitable substance is contained in the primer cap and held in place by a tin-foil disk. This explosive sub- stanceisreadily projectile set off by shock and is driven against the anvil block by the hammer of the gun on firing. The flash created passes through the anvil by way of small flash holes leading through the anvil nose to the cavity in which the soft brass ball is loosely confined, then through the flash holes in the plug, destroying the paper disk \! cemented to

^N CAR ^|g GE the top of the plug to prevent the powder in the magazine of the primer from working down through the flash holes. On the under side of the closing-in disk is another disk of paper to prevent the escape of the magazine powder charge through its flash slits. The flash transmitted through the anvil and plug from the explosion of the primer cap ignites the powder in the magazine, which, in turn, ignites the pro- pelling charge in the cartridge case proper. primer The flame from the primer

��The primer ignites the charge in the cartridge case to drive the projectile from the gun on its deadly mission

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��magazine breaks through this^second paper disk and escapes through the radiating flash-slits in the closing-in disk.

The explosion of the charge in

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