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Chorge: 22.62 # Comp B Distance 24 ft Scale I fringe =! 67PSI Shape cylindrical
Fig. 7. Blast-pressure curve of small charge showing three separate shocks arriving at gauge.
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Time in Milliseconds
Fig. 8. Pressure-time plot of internal pressure developed by a typical large-caliber rifle.
Moraine Products Division of General Motors Corp. "Porex" is made of a large number of small beads which are bonded on their outer edges by heat and pressure until the whole unit is quite rigid but leaving a fair percentage of air passage between the balls. The "Porex" after manufacture is dipped into hot paraffin and the excess paraffin blown out with compressed air. This leaves each individual ball coated with a very thin layer of paraffin which will not be wet with water droplets. A "Porex" filter thus treated will not pass water even though it is immersed onequarter inch or so. A blast gauge thus
protected can be left out in the dust and rain even though its sensitive diaphragm is turned up flush with the ground. By keeping the volume of air small and the area of the "Porex" disc large, the flow time is so rapid that it does not measurably decrease the frequency response of the diaphragm.
Records
It is difficult to find a practical record that can be displayed on a magazine page, as most events of interest are a number of milliseconds long and would require many feet of paper to present them adequately. The record of Fig. 6
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November 1952 Journal of the SMPTE Vol. 59