88 
rochleder's  proximate  analysis. 
is  treated  with  ether,  whereby  the  lead  compounds  of  the  liquid  fatty  acids 
are  dissolved,  but  not  those  of  the  solid  fatty  acids,  and  which,  after  being 
washed  with  ether,  are  decomposed,  which  can  be  accomplished  either  by 
spirit  containing  sulphuric  or  hydrochloric  acid,  or  by  treatment  with  spirit 
and  sulphuretted  hydrogen.  The  fatty  acids,  freed  from  lead,  and  dissolved 
in  spirit,  are,  after  the  greatest  portion  of  the  spirit  has  been  distilled  off, 
mixed  with  a  solution  of  carbonate  of  potash  as  long  as  an  effervescence 
thereby  ensues,  and  then  the  spirit  is  entirely  expelled  by  evaporation.  A 
little  solution  of  caustic  potash  is  now  added,  and  the  whole  boiled  to  de- 
compose a  small  quantity  of  the  ethers  of  the  fatty  acids,  which  have  formed 
by  the  decomposition  of  the  lead  salts  with  the  spirit  containing  sulphuric 
or  hydrochloric  acid,  and  by  the  distillation  of  the  spirit,  have  not  quite 
volatilized,  and  to  combine  the  fatty  acids  contained  therein  with  potash. 
The  excess  of  alkali  is  separated  by  salting  the  soap,  which  is  then  dis- 
solved in  water.  This  solution  of  the  potash  salts  of  several  fatty  acids  is 
now  fractionally  precipitated  with  acetate  of  magnesia,  acetate  of  baryta,  or 
acetate  of  lead,  according  to  the  method  of  Heintz,  by  adding  half  of  a  solu- 
tion of  these  salts,  which  would  have  sufficed  to  throw  down  the  whole  of 
the  fatty  acids.  The  precipitate  is  filtered  off,  and  washed.  To  the  filtrate, 
the  second  half  of  the  solution  of  the  acetate  employed  is  added,  and  the 
precipitation  is  thus  completed.  Both  precipitates  are  now  decomposed, 
and  both  resulting  portions  of  the  fatty  acids  are  converted  into  ammonia- 
cal  salts  in  solution,  and  these  solutions  each  again  divided  into  two  parts, 
and  precipitated  by  the  acetate  selected.  This  method  of  separation  is 
continued  until  only  one  fatty  acid  is  in  combination  with  magnesia,  lead, 
or  baryta,  in  the  individual  parts.  We  learn  whether  the  separation  has 
been  brought  thereby  to  this  point  by  decomposing  a  portion  of  a  lead 
magnesia,  or  baryta  salt,  converting  the  fatty  acid  or  acids  into  a  silver 
salt,  and  determining  the  atomic  weight  of  the  acid  by  heat.  The  bulk  of 
the  lead,  magnesia,  or  baryta  salt  is  then  decomposed,  of  which  a  small 
portion  has  been  taken  for  the  preparation  of  the  silver  salt  used  for  the 
determination  of  the  atomic  weight ;  the  resulting  free  acids  converted  into 
ammoniacal  salts,  and  these  fractionally  precipitated.  After  a  silver  salt 
has  been  prepared  from  the  first  and  second  half,  the  atomic  weights  of  both 
silver  salts  are  determined.  When  the  atomic  weight  or  the  organic  sub- 
stance of  both  silver  salts  is  the  same,  and  equal  to  the  atomic  weight  of  the 
silver  salt  first  estimated,  the  separation  in  this  examined  portion  has 
been  a  complete  one. 
If  not  only  glyceryle  compounds  of  the  non-volatile  fatty  acids,  but  those 
of  the  volatile  acids,  are  contained  in  the  fats,  the  method  is  modified  in 
the  following  way  : — The  saponification  is  performed  in  a  still,  the  solution 
of  soap  therein  mixed  with  a  solution  of  tartaric  acid,  and  the  whole  sub- 
jected to  distillation.  After  the  head  has  been  fixed,  and  a  careful  ar- 
rangement made  for  cooling,  the  volatile  fatty  acids  are  then  found  in  the 
distillate,  the  non-volatile  ones  among  the  contents  of  the  still.    The  distil- 
(To  be  continued.) 
