In  the  usual  and  more  convenient  form  of
air-pump,  a  brass  tube  passes  from  the  bottom
of  the  syringe  and  terminates  in  the  centre  of
a  disk  of  brass  or  glass  ground  accurately  j
the  vessel  from  which  the  air  is  to  be  exhausted
has  its  edge  very  accurately  ground,  and  is
mounted  upon  the  plate  as  shown  in  the  sub-
joined figure.
syringe,  which  consists  of  a  cylinder  fitted  with
a  stop-cock,  and  having  a  valve  at  the  bottom


Air-pump,  Bnnsen's  Water.    (See  figure  on
page  53.)

This  consists  of  a  wide  glass  tube,  a,  into
which  another  tube,  J,  i',  b",  passes  air-tight.
