102  Alcohol  in  Concentrated  Nitrous  Ether.  {AmM£Sh,3o£rM* 
will  be  lost,  and  the  error  is  not  large  because  only  from  10  to  20 
per  cent,  of  this  is  alcohol 
Various  forms  of  apparatus  were  used,  at  first  merely  connecting 
with  upright  condensers  and  allowing  the  nitrous  ether  to  evaporate 
at  room  temperature ;  later  a  modification  of  this  method  was 
adopted,  which  works  quite  satisfactorily.  The  flask  is  connected 
with  an  upright  spiral  condenser  and  in  the  top  is  poured  ice- water. 
If  the  lower  opening  is  quite  small,  a  spiral  column  of  ice-water 
will  be  held  in  the  condenser  by  the  pressure  developed  by  the  vol- 
atilizing concentrated  nitrous  ether,  and  will  necessitate  each  bubble 
of  gas  passing  through  this  spiral  column  of  cold  water.    (Fig.  1.) 
