362 



Popular Science Monthly 



FLASH SLIT 



CLOSING DISK 

 LUG 



PRIMER CAP 



RIMER BODY 



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 



