water),  amounting  from  ^th  to  ^Suth  of  the
volnme  of  the  air,  is  then  introduced  into  the
measuring  tube  by  means  of  a  pipette  with  the
point  bent  upwards  (see  drawing),  and  spread


over  the  entire  inner  surface  of  the  tube  by
shakin.'  the  latter.  When  no  further  diminu-
tion of  volume  takes  placb  the  decrease  is  rend
off.     The  carbonic  acid  is  thus  removed.
3.  A  solution  of  pyrogallic  acid  containing
1  gramme  of  the  acid  in  5  or  6  c.  c.  of  water
i<  introduced  into  the  same  measuring  tube
by  menus  of  another  pipette  similar  to  the
above.  The  mixed  fluid  (the  pyrogallic  acid
and  the  solution  of  potash)  is  spread  over  the
Inner  surface  of  the  tube  by  shaking  the
latter,  and  when  no  further  diminution  of
volnme  is  observed  the  residuary  nitrogen  is
measured.
4.  The  solution  of  pyrogallic  acid  mixing
with  the  solution  of  potash  of  course  dilutes
it,  causing  thus  an  error  from  the  diminution
of  its  tension ;  but  this  error  is  so  trifling  that
it  lias  no  appreciable  influence  upon  the
results.  It  may,  moreover,  be  readily  cor-
rected by  introducing  into  the  tube,  after  the
absorption  of  the  oxygen,  a  small  piece  of
hydrate  of  potash,  corresponding  to  the
amount  of  water  in  the  solution  of  the  pyro-
gallic acid.
There  is  another  slight  error  on  account
of  a  portion  of  the  fluid  adhering  to  the  inner
surface  of  the  tube,  so  that  the  volume  of  the
ga'i  is  never  read  off  with  absolute  accuracy.
In  conducting  these  endiometrio  experi-
ments the  necessary  corrections  for  tempera-
ture and  barometric  pressure  must,  of  course,
be  made.
