The vats are also provided with false bottoms, outlet cocks, steam pipes and so forth.
Both fixed and rotating vats are employed, the chlorination proceeding more rapidly in the latter case; rotating barrels are sometimes used.
For open pools and dams Schenck substitutes large wooden vats under cover, into which the flax is tightly packed in an upright position.
In spite of all precautions a certain quantity of impurities is always formed, but this should be kept down as much as possible by strictly watching the temperature in the vats and by taking care that the black-ash in the wet state is never exposed to the air.
Moreover, the high potential difference between the terminals of the series tank introduces a greater danger of shortcircuiting through scraps of metal at the bottom of the bath; for this reason, also, lead-lined vats are inadmissible, and tarred slate tanks are often used instead.