642  Mr.  Inglis  on  the  Isothermal  Distillation  of 
The  circulation  of  the  vapour  is  carried  on  by  means  o£  the 
mercury  circulator  DEFGr  of  the  pattern  described  by  Collie 
(Journ.  Ohem.  Soc.  1889,  p.  110).  Mercury  flows  from  the 
reservoir  D  through  a  rubber  tube  furnished  with  a  screw- 
clip  and  then  falls  in  drops  down  the  tube  EF.     As  each 
Fis-.  1. 
drop  falls  it  drives  on  the  gas  contained  in  the  tube  EF  and 
pumps  gas  in  the  direction  KLHE.  In  this  way  the  circu- 
lator pumps  the  vapour  up  the  tube  3  and  blows  it  down  2, 
