THE PRODUCTION OF EXPLOSIVES 145 



land and it constituted one of the most notable achievements 

 in physical chemistry as applied to explosive substances. An 

 equally notable engineering achievement was the building of 

 a plant at Perry ville, Maryland, in about 100 days in which 

 to produce 300 long tons of ammonium nitrate daily by this 

 process. The plant was built of concrete, tile and steel of the 

 most approved construction and cost about fourteen and a 

 quarter millions of dollars. The results of its operation ex- 

 ceeded all requirements. 



An achievement of a quite different character but of the 

 highest order in novelty and importance was that of using 

 crystals, such as those of tourmaline, quartz or sugar, with 

 which to measure the pressures exerted by explosives as they 

 explode. It is important to know this with a high degree of 

 precision for use in designing and operating guns, in charging 

 mines and planning explosives operations. Heretofore at- 

 tempts to measure these pressures have been made by the de- 

 formation of disks of copper or lead of known form and di- 

 mensions, but since the inertia of these bodies must be first 

 overcome and, since, owing to elasticity, they tend to regain 

 their original form and dimensions, the methods were in error 

 to an unknown extent. It was known that when asymmetric 

 crystals, such as those of tourmaline, quartz or sugar, were 

 subjected to pressure they acquired electric charges, which 

 M. Curie had found were proportioned to the pressures put 

 upon the crystal, and the electricity thus generated by pressure 

 was styled piezo-electricity. Sir J. J. Thomson applied piezo- 

 electricity to the determination of the explosion pressures of 

 submerged guncotton by placing a plate of tourmaline within 

 the primary explosion area, the plate being connected on each 

 face to a conductor which led to an aperture through which a 

 stream of electrons emitted from a heated tungsten filament 

 was led, and the extent to which this stream was deflected was 

 then noted. Or, in order to produce a pressure-time curve, the 

 stream of electrons was at the time of deflection exposed to the 

 influence of a rapidly alternating magnetic field. This method 



