Doubler

n.
  1. One who, or that which, doubles.
  2. (Elec.) An instrument for augmenting a very small quantity of electricity, so as to render it manifest by sparks or the electroscope.
  3. A part of a distilling apparatus for intercepting the heavier fractions and returning them to be redistilled.
  4. (Calico Printing) A blanket or felt placed between the fabric and the printing table or cylinder.