rochleder's  proximate  analysis. 
177 
(Continued  from  page  88.) 
late  is  so  fractioned  by  partial  combination  with  a  base,  and  distillation 
as  described  in  the  examination  of  the  watery  distillate  (page  280,  vol.  ix.) 
which  is  obtained  by  the  decoction  of  the  material  under  examination  with 
water.  The  non-volalile  fatty  acids,  partly  solid  and  partly  fluid,  are  treated 
precisely  as  though  they  had  been  obtained  by  saponification  from  the 
fatty  mixture  alone,  which  was  above  spoken  of. 
The  liquid  fatty  acids,  which  are  obtained  as  ethereal  solutions  of  their 
lead  salts,  by  the  treatment  as  above  given  of  the  salts  of  the  fatty  acids 
with  ether,  may  be  likewise  mixtures  of  several  liquid  fatty  acids.  After 
the  expulsion  of  the  ether  they  must  be  separated  from  the  lead  and  thrown 
down  by  fractional  precipitation  from  one  another,  precisely  as  stated  for 
the  solid  fatty  acids. 
Since  it  has  been  discovered  that  not  only  fatty  acids,  but  also  benzoic 
acid,  may  be  contained  in  fatty  mixtures  as  a  glyceryle  compound,  it  is  no 
longer  improbable  that  the  glyceryle  compounds  of  other  acids  besides 
those  of  the  proper  fatty  acids,  may  be  found  in  many  fats  when  attention 
is  directed  thereto. 
To  ascertain  whether  other  acids  besides  the  fatty  are  contained  or  not  as 
glyceryle  compounds  in  the  mixture  of  fats,  the  fluid  which  is  obtained  when  the 
fat  is  saponified,  and  the  soap  separated  by  common  salt,  is  filtered  and  evapor- 
ated in  a  water  bath  until  it  is  reduced  to  a  very  small  volume.  Glycerine 
and  common  salt  are  always  found  in  this  residue,  besides  free  potash,  car- 
bonate of  potash,  and  small  quantities  of  dissolved  soap.    If  glyceryle  com- 
pounds of  benzoic  acid  or  of  other  acids  were  contained  besides  in  the  fat,  the 
potash  salts  of  the  acids  are  dissolved  likewise  in  this  fluid.    The  residue, 
which  is  obtained  by  evaporation,  is  divided  into  two  parts.    The  first  part  is 
mixed  with  a  solution  of  chloride  of  calcium,  which  precipitates  a  little 
carbonate  of  lime  as  well  as  the  compounds  of  smaller  quantities  of  fatty 
acids  with  lime,  which  are  insoluble  in  water.    The  lime  salt  of  the  acid, 
which  is  present  in  addition  to  the  fatty  acid,  either  precipitates  or  remains 
dissolved.    If  it  remains  dissolved,  a  solution  of  the  salt  of  the  acid  sought 
for  is  obtained  by  filtering  the  fluid  from  the  carbonate  of  lime,  as  well 
as  from  the  lime  salts  of  the  fatty  acids  ;  but  the  solution  is  contaminated 
with  glycerine  and  common  salt.    This  fluid  is  evaporated  to  concentrate 
it.    The  residue  is  mixed  with  hydrochloric  acid.    If  benzoic  acid,  or  any 
acid  difficultly  soluble  in  cold  water,  is  present,  it  is  precipitated  by  the 
addition  of  hydrochloric  acid.    When  nothing  is  thrown  down,  either  no 
acid  or  one  very  soluble  in  water  was  present.    To  arrive  at  certainty  on 
this  point,  a  second  portion  of  the  residue  of  evaporation  above  mentioned 
is  precipitated  with  chloride  of  calcium,  the  resulting  precipitate  collected 
and  washed  with  water,  diffused  in  a  little  water  and  mixed  with  dilute 
sulphuric  acid.    The  decomposition  is  promoted  by  heat  until  it  is  com- 
pleted. The  fluid,  still  hot,  is  then  filtered  through  a  moist  filter.    If  with 
the  fatty  acids,  another  acid  is  precipitated  by  chloride  of  calcium,  as  a 
12 
