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Progressive burning coated powders, usually flakes or single-perforated short cylinders, are made by treating the grains with a gelatinizing agent, or non-volatile, non-explosive solvent for nitrocellulose, dissolved in a volatile liquid, generally benzene or acetone, tumbling them together in a sweetie barrel or similar device, and evaporating off the volatile liquid by warming while the tumbling is continued. The material which is applied as a coating is known in this country as a deterrent, in England as a

Figure 80. Cross Section and Longitudinal Section of a Grain of 50 Caliber Extruded Smokeless Powder, Deterrent Coated (25X). (Courtesy Western Cartridge Company.)

moderant. At the time of the first World War si/m-diinethyldi-phenylurea was already used widely as a deterrent in rifle powder intended for use in shooting matches and in military propellants designed to produce especially high velocities. The substance was called centralite because its use had been developed in Germany at the Central War Laboratory at Spandau. The ethyl analog, diethyldiphenylurea, at first known as ethyl ccntralite, is usually called Ccntralite No. 1 and has generally superseded the methyl compound (or Ccntralite No. 2) for use in smokeless powder. Although many other substances have been tried and have been patented, this remains the most widely used of any. Butyl cen-tralite is a better gelatinizing agent for nitrocellulose than either

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