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- A filter traps dust from the air .
- Under appropriate conditions a multilayer may also be employed as a filter .
- It is possible to use a plutonium foil as a filter to remove the second-order contamination .
- A satisfactory approximation to monochromatic light can be obtained with a filter placed in front of the arc .
- The crude dye is collected on a filter and then recrystallized from ethanol containing a small amount of piperidine .