562 
rochleder's  proximate  analysis. 
hydrochloric  acid  gives  crystallized  grape  sugar ;  on  the  contrary,  by  treat- 
ment with  baryta  water,  a  carbohydrate  with  the  decided  character  of  an 
acid.  The  thujine  from  the  green  parts  of  Thvja  occidentalis  treated  with 
hydrochloric  acid  affords  a  non-crystallizable  carbohydrate  ;  on  the  con- 
trary, by  treatment  with  baryta  water,  crystallized  grape  sugar.  Inde- 
pendently of  this  difference,  a  number  of  substances  still  exists  which,  by 
treatment  with  baryta,  do  not  set  free  a  carbohydrate,  as  is  the  case  by  the 
action  of  hydrochloric  acid,  but  an  acid  results  which  combines  with  the 
baryta,  while  a  substance  is  formed  \vhich,  by  the  action  of  acids,  affords 
sugar  and  a  second  decomposition  product.  Thus  populine,  by  treatment 
with  baryta,  gives,  besides  benzoate  of  baryta,  salicine,  and  ononine,  besides 
formiate  of  baryta  affords  formonetine.  Salicine  as  well  as  formonetine 
are  copulated  sugar  compounds. 
It  will  be  seen  from  the  examples  cited  that  the  behaviour  of  a  substance 
of  that  kind  to  hydrochloric  acid  renders  in  no  way  superfluous  the  study 
of  its  relations  to  an  alkali. 
In  consequence  of  the  facility  with  which  organic  substances  oxydize  in 
contact  with  an  alkali  in  the  oxygen  of  the  air,  it  is  necessary  to  under- 
take the  treatment  with  baryta  in  an  atmosphere  of  hydrogen.  To  accom- 
plish this,  an  aqueous  solution  of  the  substance  under  examination,  as 
concentrated  as  possible,  is  introduced  into  a  flask  which  is  closed  with  a 
cork  having  three  perforations.  Through  one  perforation  a  glass  tube 
passes  which  is  bent  at  an  angle,  and  serves  to  connect  the  flask  with  a  re- 
frigeratory apparatus,  and  a  receiver  for  the  collection  of  the  volatile  de- 
composition products  evolved.  Through  the  second  perforation,  a  glass 
tube  bent  at  a  right  angle  passes  almost  to  the  bottom  of  the  flask,  through 
which  the  hydrogen  enters  into  the  flask  to  drive  out  the  air.  The 
hydrogen  is  generated  from  granulated  zinc  and  water  by  sulphuric  acid, 
and  first  conducted  through  a  washing  buttle  containing  a  solution  of  bi- 
chloride of  mercury  for  the  separation  of  the  sulphuretted  and  arseniuretted 
hydrogen  before  it  passes  into  the  fluid.  Through  the  third  perforation  the 
long  beak  of  a  funnel  is  stuck,  which  can  be  rendered  air  tight  by  a  glass 
rod  ground  in  above  where  the  beak  of  the  funnel  begins.  This  funnel  is 
filled,  when  ail  the  air  is  displaced  by  hydrogen,  with  a  concentrated  hot  so- 
lution of  the  hydrate  of  baryta  in  water.  By  raising  the  glass  rod  the  baryta 
is  allowed  to  flow  into  the  flask,  which  is  closed  before  the  last  drops  have  run 
in.*  The  baryta  water  may  be  thus  introduced  into  the  flask  without  a  trace 
of  air  coming  in  contact  with  the  contents  of  the  flask.  Often  an  insoluble 
compound  of  baryta  with  the  organic  substance  results,  so  that  a  dense  pre- 
cipitate is  formed.  In  this  case  the  flask,  which  is  heated  on  a  sand-bath, 
must  be  frequently  shaken,  to  prevent  a  deposition  of  the  precipitate.  Gener- 
*  When  the  hydrogen  gas  is  evolved  from  a  flask,  the  necessary  mixture  of 
sulphuric  acid  and  water  for  the  continued  development  of  the  gas  must  be 
passed  in  through  a  funnel  constructed  in  the  same  manner  to  prevent  the  in* 
-gress  of  the  air  into  the  bottle. 
