The "first runnings" of liquid from a filter are commonly foul, and are pumped back or returned until the fluid runs perfectly limpid and transparent, when it is "turned into" the"filtered liquor cistern," or proper receiver. In many cases the liquid does not readily become transparent by simply passing through the filter; hence has arisen the use of filtering powders, or substances which rapidly choke up the pores of the media in a sufficient degree ta make the fluid pass clear.