402 
Bunsens  Water-Air  Pump,  etc.  { 
Am.  Jour.  Pharm. 
Sept.  1, 1871. 
thus  produce,  under  proper  precautions,  a  partial  vacuum.  The  water- 
blast,  the  mercury  air-pump,  and  the  pneumatic  apparatus  for  con- 
veying letters  and  packages  from  one  place  to  another,  are  constructed 
upon  the  same  principle,  a  partial  vacuum  being  made  by  the  fall  of 
water  or  some  other  liquid. 
The  most  convenient  form  of  a  water  air-pump,  adapted  for  chemi- 
cal operations  and  for  expe- 
riments in  natural  philoso- 
phy, is  shown  in  the  cut.  A 
is  a  glass  cylinder,  to  the 
upper  part  of  which  a  nar- 
rower glass  tube  h  is  herme- 
tically fused,  so  that  its  low- 
er end  reaches  to  near  the 
narrowed  portion  of  a,  while 
the  upper  end  is  connected 
with  the  heavy  gum  tubing 
k;  another  gum  tube  con- 
nects a  at  the  base  with  the 
lead  pipe  d.    Near  the  top 
of  a  a  short  glass  tube  is  in- 
serted, to  connect  it  with  the 
water  by  means  of  the  gum 
hose     the  flow  of  the  water 
being  regulated  by  more  or  less  compres- 
sing the  hose  with  the  steel  spring 
which  is  worked  by  the  screw  s.  The 
water  entering  through      fills  a  around 
the  tube  5,  and  runs  off  through  con- 
tinually sucking  air  out  of  h. 
These  are  the  main  parts  of  this  water 
air-pump,  all  others  being  of  less  import- 
ance. The  apparatus  having  been  joined 
by  means  of  the  gum  tubing  h  with  the 
vessel,  from  which  the  air  is  to  be  re- 
moved ;  the  air  enters  deposits  any 
moisture  that  may  have  been  carried 
over,  and  passes  through  the  bent  glass 
tube  /  into  5,  from  where  it  is  continually  removed  by  the  falling 
