178 
rochleder's  proximate  analysis. 
lime  salt  insoluble  in  water,  it  must  be  contained  in  this  filtrate  with  a 
little  free  sulphuric  acid.  To  discover  the  presence  of  an  acid,  which  is 
neither  difficultly  soluble  in  water,  nor  gives  with  lime  an  insoluble  salt, 
we  proceed  in  the  following  way  : — 
A  portion  of  the  fat  under  examination  is  saponified  by  boiling  with  thin 
milk  of  lime,  and  the  hot  fluid  containing  glycerine  is  filtered  from  the 
lime  soap.  Carbonic  acid  is  conducted  into  the  filtrate,  heated  for  the  de- 
composition of  the  bicarbonate  of  lime,  and  filtered.  The  filtrate  contains 
the  lime  salt  of  the  acid  sought  for  and  glycerine.  The  fluid  is  mixed 
with  basic  acetate  of  lead,  and  the  precipitate  perchance  resulting  is  sepa- 
rated by  filtration  from  the  fluid.  The  lead  salt  is  washed  with  water,  dif- 
fused in  water,  and  decomposed  by  sulphuretted  hydrogen.  In  the  fluid 
filtered  from  the  sulphuret  of  lead,  the  acid  sought  for  is  contained.,  There 
are  only  a  few  acids  which  produce  no  precipitate  with  basic  acetate  of 
lead.  Should  such  an  acid  be  present  instead  of  basic  acetate  of  lead,  a 
solution  of  nitrate  of  silver  mixed  with  a  little  ammonia  is  added,  which 
precipitates  a  silver  salt  of  the  acid.  If  in  this  way  no  precipitation  results, 
the  concentrated  fluid,  wherein  the  acid  and  glycerine  exist  in  solution,  is 
digested  with  freshly  precipitated  carbonate  of  zinc  or  copper,  and  abso- 
lute alcohol  is  added  to  the  filtered  fluid,  by  which  a  zinc  or  copper  salt  of 
the  acid  is  thrown  down,  but  not  the  glycerine.  When  an  acid  which  is 
volatile  is  mixed  with  the  glyceryle  compound  in  the  fat,  it  will  have  been 
already  found  in  the  examination  of  the  volatile  fatty  acids. 
When  fats  and  resins  are  mixed  with  one  another,  the  mixture  is  treat- 
ed with  a  solution  of  caustic  potash  to  effect  the  saponification  of  the  fats. 
The  electro. negative  resins  dissolve  likewise  as  potash  compounds  therein, 
while  the  indifferent  resins  remain  undissolved.  After  the  insoluble  part 
of  the  resin  has  been  separated,  the  solution  of  soap  and  resin  soap  is  treat- 
ed with  common  salt,  and  the  soap  of  the  fatty  acids  is  separated,  but  not 
the  resin  soap.  The  soap  which  has  separated  is  treated  as  previously  des- 
cribed (page  87).  The  solution  of  resin  soap,  which  at  the  same  time  con- 
tains the  glycerine  of  the  fat,  is  mixed  with  dilute  hydrochloric  or  sulphuric 
acids,  whereby  the  resinous  acids  are  separated.  They  often  agglomerate, 
particularly  when  heated,  and  may  be  easily  taken  from  the  fluid  and  fur- 
ther purified.  Sometimes  it  is  necessary  to  evaporate  the  liquid,  because  a 
milky  fluid  results  with  acids  which  will  not  filter  clear.  The  resinous  acids 
separated  are  again  dissolved  in  a  solution  of  potash,  and  mixed  with  an 
excess  of  a  strong  solution  of  potash.  By  these  means  frequently  a  sepa- 
ration of  several  resinous  acids  is  effected.  Many  potash  salts  of  the  resins 
are  soluble,  while  others  are  insoluble  in  a  concentrated  solution  of  pot- 
ash. 
Before  I  conclude,  the  consideration  of  the  mixtures  of  resins  and  fats 
separated  from  the  spirituous  extract,  by  cooling  or  distilling  off  the  alco- 
hol, I  must  direct  attention  to  a  point  in  the  treatment  of  resins.  Some 
resins  are  copulated  compounds.  Two  resins  are  already  known  which  break 
