rochleder's  proximate  analysis. 
87 
precipitate  of  organic  substances  results,  which,  as  stronger  acids,  were  not 
thrown  down  by  the  carbonic  acid  from  the  lime.  The  lime  salt,  prepared 
by  precipitating  with  chloride  of  calcium,  the  solution  which  was  obtained 
by  means  of  potash,  is,  after  it  is  dried,  treated  with  ether,  which  generally 
dissolves  a  portion  of  it,  which  is  left  behind  by  distilling  off  the  ether  in  a 
water  bath.  The  portion  remaining  undissolved  in  ether  is  treated  with 
alcohol,  which  sometimes  likewise  dissolves  a  small  portion.  Lastly,  that 
which  is  insoluble  in  ether  and  alcohol,  is  treated  with  dilute  hydrochloric 
acid  without  the  application  of  heat,  for  the  separation  of  the  lime.  With 
these  individual  portions  we  shall  have  the  opportunity  of  ascertaining 
which  method  of  separation  possesses  the  advantage  over  the  others,  and  to 
treat  correspondingly  the  whole  mass  of  the  resinous  mixture. 
When  we  have  to  operate  on  a  mixture  of  fats  which  has  been  procured 
either  by  pressure  between  cold  or  heated  plates,  or  by  the  extraction  of 
the  material  with  hot  spirit,  and  distilling  off  the  spirit  and  filtering  the 
watery  residue  through  a  moist  filter,  whereby  the  fat  remains  on  the  filter, 
we  proceed  in  the  following  way  : — 
A  small  portion  of  the  fat  is  saponified  with  a  solution  of  potash  in  a  dish, 
the  solution  of  soap  decomposed  by  a  sufficient  quantity  of  dilute  sulphuric 
acid,  and  the  floating  fatty  mass  separated  from  the  watery  fluid  by  a 
pipette  or  a  small  syphon  ;  this  fluid  is  subjected  to  distillation  in  a  flask 
or  a  retort,  after  a  refrigeratory  apparatus  and  receiver  have  been  con- 
nected with  the  distilling  vessel.    The  distillate  ia  tested  after  about  two- 
thirds  of  the  fluid  have  passed  over,  and  the  distillation  is  interrupted  to 
ascertain  whether  it  has  or  not  an  acid  reaction,  whether  turbid  or  clear, 
whether  oily  globules  have  separated  thereout,  and  whether  it  possesses  an 
odor  or  not.    When  the  distillate  exhibits  only  a  slight  acid  reaction,  is 
almost  odorless,  quite  clear,  and  no  oily  globules  float  on  its  surface,  no 
glyceryle  compounds  of  the  volatile  fatty  acids  are  present  in  quantity.  On 
the  other  side,  they  are  present  when  the  distillate  has  a  strong  acid  re- 
action, has  thrown  out  oily  globules,  or  at  least  when  these  render  the 
distillate  turbid  or  opalescent,  and  has  a  remarkable  odor.     If  no  volatile 
fatty  acids  are  present,  the  bulk  of  the  fatty  mixture  is  saponified  with  a 
solution  of  potash,  the  solution  of  soap  mixed  with  common  salt,  and  the  soap 
formed  is  separated.    The  soap  is  removed  after  some  time  from  the 
aqueous  fluid,  and  dissolved  in  water  with  the  aid  of  heat.    The  solution  is 
again  treated  with  common  salt,  and  the  solution  and  the  salting  repeated 
frequently,  until  the  watery  saline  fluid  takes  up  no  more  foreign  sub- 
stances.   In  the  first  ley,  from  which  the  soap  has  been  separated  by  com- 
mon salt,  is  contained  the  chief  bulk  of  the  glycerine;  the  soap  which  has 
been  purified  by  repeated  solution  and  salting,  is  now  dissolved  in  water, 
and  precipitated  with  a  solution  of  sugar  of  lead;  the  precipitate  which 
results  is  a  mixture  of  lead  compounds,  consisting  of  the  lead  salts  of  the 
fatty  acids.    This  mixture  of  lead  salts,  after  it  has  been  washed  and  dried, 
