Page:Popular Science Monthly Volume 91.djvu/378

This page needs to be proofread.


��Popular Science Monthly





��How the primer works. It is composed of six parts, each of which has a very distinct and definite duty to perform

the magazine creates gases, some of which attempt to escape by passing back through the flash holes in the plug, and this is where the soft metal ball previously mentioned comes into action. The gases impinge against this ball, and drive it into the base of the cavity where it acts as a cork, stop- ping up the passage and effectually pre- venting the gases from escaping through the base of the primer. This little ball there- fore forms an invaluable safeguard both to the gun and the gunner, at the same time insuring the efficiency of the primer.

Such is the operation of the primer. It is an ingenious little mechanism without which the shell would be comparatively harmless and might be thrown about, dropped or otherwise maltreated without danger of explosion. As for the primer itself, it would be no more dangerous, if it were not for the explosive cap in its base, than a shotgun cartridge with its cap removed. In fact, the primer of an artillery shell can be likened to an'ordinary blank cartridge.

Although primers are completely as- sembled in the arsenals or factories in which they are manufactured, they are usually not inserted into the cartridge case until the projectile is being prepared for use — probably behind the lines on the battlefield. The transportation, therefore, of artillery ammunition can be undertaken with little liability of accident through explosion. The active agent controlling the destruc- tiveness of artillery shells, i. e., the primer, constitutes the one dangerous part of the shell, but separate from the cartridge case, the primer, even with its cap fitted, can do little damage. A blow on the charged primer cap is necessary to start things.

��Making Highways on the Mud -Pie Principle

SOME enterprising folk 1 in the Imperial Valley desert, near Coachella, California, have discover- ed an easy and exception- ally inexpensive method of securing public high- ways without employing other labor than that necessary to flood the highway area with water. In this simple way other- wise impassable desert paths are converted into excellent hard adobe, which makes as fine an automobile road as asphalt.

The highway in the accompanying illus- tration is invisible; it is two to three inches beneath the water. But when the water is drained off and the blistering hot sun bakes the wet ground into one long ribbon of a mud-pie, it does not loosen under the heaviest of traffic. Sluiceways are first constructed through the proposed highway and the irrigation waters from nearby ditches are then turned into them. After the water has soaked into the ground it is shut off; any remaining water is led into the fields and used again. The treatment costs nothing more than the labor necessary to dig the sluiceways.

The success of this method of quick road-construction depends upon the clayey character of the soil.

���When the water has been drained off, a hard, sun-baked adobe highway will result

�� �