>    RAW  MATERIALS  OF  SOAP-MANUFACTURE.  4!

The  length  of  time  required  to  satisfactorily  "  cook  "  the  stock  depends
upon  the  amount  and  character  of  the  charge.  A  tank  with  a
yielding  capacity  of  25  tierces  is  generally  6  feet  in  diameter  and


FIG.  8. — Packers'  Rendering-tank.
12  feet  high  and  requires  from  eight  to  ten  hours  for  cooking.  No
water  is  added  during  the  rendering  period,  sufficient  resulting  from
the  condensation  of  the  steam.  Should  this  increase  excessively,
which  condition  can  be  ascertained  by  the  rendered  stock  blowing


42  AMERICAN  SOAPS,  CANDLES,  AND   GLYCERIN.
