rochleder's  proximate  analysis. 
563 
ally,  the  decomposition  proceeds  more  rapidly  with  baryta  than  with  hydro- 
chloric acid.  Upon  the  termination  of  the  decomposition  the  flask  is  al- 
lowed to  cool,  in  a  continuous  current  of  hydrogen.  Either  a  clear  solu- 
tion results,  consequently  no  insoluble  baryta  compound  has  been  formed, 
or  such  is  suspended  in,  or  deposited  at  the  bottom  of,  the  fluid.  Instead 
of  hydrogen  gas,  either  carbonic  acid  gas  is  conducted  into  the  flask,  or 
dilute  sulphuric  acid  is  poured  in  through  the  funnel  which  is  capable  of  be- 
ing closed.  Both  operations  are  intended  to  convert  the  excess  of  baryta 
into  a  carbonate  or  a  sulphate.  By  the  sulphuric  acid  always,  and  some- 
times by  the  carbonic  acid,  the  baryta  compound  of  the  decomposition  pro- 
duct formed  is  decomposed.  Whether  carbonic  acid  or  sulphuric  acid 
should  be  used  must  be  ascertained  by  an  experiment  which  is  made  with 
a  small  portion  of  the  contents  of  the  flask.  In  this  preliminary  experi- 
ment carbonic  acid  is  employed,  and  it  is  observed  whether  by  filtering  the 
fluid  in  contact  with  the  air  it  undergoes  a  change.  If  no  change  happens, 
carbonic  acid  should  be  conducted  through  the  fluid  in  a  large  quantity. 
On  the  contrary,  if  it  changes  in  the  air,  the  bulk  of  the  fluid  must  be 
treated  with  sulphuric  acid.  Some  substances  are  oxidized  in  contact  with 
carbonate  of  baryta,  but  others  are  not.  Some  compounds  which  result 
by  treatment  of  the  substances  with  baryta  water  are  almost  quite  insolu- 
ble in  water  when  an  excess  of  baryta  is  present,  and  as  this  separates  by 
the  carbonic  acid  they  dissolve,  or  from  the  compounds  formed  with  baryta, 
compounds  poor  in  baryta  are  produced  which  are  soluble  in  water,  whilst 
those  rich  in  baryta  are  insoluble.  In  such  cases  it  is  more  advantageous 
to  add  alcohol  to  the  contents  of  the  flask,  and  to  filter  the  whole.  The 
carbohydrate,  or  its  compound  with  baryta,  is  dissolved  in  the  spirituous 
fluid,  and  the  baryta  salt  of  the  second  decomposition  product  remains  on 
the  filter.  The  mass  changes  on  the  filter  when  a  readily  oxidizable  sub- 
stance is  contained  in  it.  The  carbohydrate  is  obtained  in  the  solution, 
and  may  be  obtained  pure  by  distilling  off  the  spirit  and  carefully  pre- 
cipitating the  baryta  by  sulphuric  acid  and  then  evaporating  the  fluid  free 
from  baryta. 
As  it  is  desirable  by  treatment  with  baryta  to  test  portions  of  the  ma- 
terial, wh&ther  treated  with  carbonic  acid  or  sulphuric  acid,  or  mixed  Avith 
alcohol,  without  bringing  the  whole  mass  of  the  fluid  into  contact  with  the 
air,  I  will  here  describe  a  method  by  which  portions  can  be  used  for  the 
preliminary  investigation  without  bringing  the  entire  quantity  of  the  fluid 
from  which  these  portions  are  taken  into  contact  with  the  air.  For  this 
purpose,  the  end  of  the  glass  tube  is  closed  through  which  the  hydrogen 
gas  and  the  aqueous  vapor  pass  out,  and  the  glass  rod  is  loosened  by 
which  the  funnel  serving  for  the  conveyance  of  the  baryta  water  into  the 
flask,  is  closed.  By  the  pressure  which  the  gas  and  vapor  exercise  on  the 
surface  of  the  fluid  in  the  flask,  the  fluid  rises  up  through  the  beak  of  the 
funnel,  and  fills  the  funnel  more  and  more  after  the  glass  rod  is  withdrawn. 
