Peilinkofcr's  Reaction. — To  the  solution  in  a  test-tube  is  added  a
little  cane-sugar  and  then  slowly  drop  by  drop  concentrated  H;S04,
shaking  well  all  the  time  and  warming  to  70°  C,  not  over,  and  cooling
if  necessary.  We  get  first  a  precipitate  of  cholic  acid,  which  redis-
snlves.  Then  when  more  HjS04  is  added  there  is  obtained,  first  a
cherry-red,  then  a  beautiful  purple  color,  which  in  eight  days  is  a
bluish-red.  This  color  i^  due  to  the  reaction  of  cholic  acid  and  the
furfurol,  which  is  formed  by  the  action  of  sulphuric  acid  on  cane-


THE    L'lilXE:    DI.VZO  TEST


151


I


I


sugar.  The  puni'c-red  solution  may  be  diUitcd  with  alcohol,  and
shows  a  characleriatic  absor|Hioii  spectnmi,  Ci^niiisiiig  siihsUinces
which  may  )ic  present  are  allniminous  bodies,  many  bodies  easily  de-
composed W  HjSO^,  many  pigmentji.  ainyl  aleohol.  and  oleic  acid;
but  in  all  these  the  absorption  *pecirnni  fails.
Udransky's  Test. — Tliis  is  the  best  test.  Furfiirol  is  used  directly.
To  1  cc.  of  the  solution  to  be  tested  is  added  i  drop  of  a  o.l  per  cent,
^vatery  fnrfurol  solution.  Tliis  is  imderlaiil  with  I  cc.  of  coiicentraied
HjSO,  and  cooled  to  restrain  the  reaction.  In  the  presence  of  only
0.033  "ip-  <*f  cholic  acid  is  obtained  a  red  color  which  after  standing
l>eco«nes  a  blood-red.  H  0,05  nig.  be  present,  one  gels  a  distinct
al}Sorption  line  in  the  spectrum.  The  spectrum  must  always  be  ex-
amined for  confirmation.  -V  10  per  cent,  cane-sugar  solution  will  give
as  good  a  test  as  a  o.i  per  cent,  fiirfurol  sohtliun.  The  red  color  must
have  a  clearly  bluish  tinge.
If  Ihc  cane-sugar  be  u*ed  in  excess  ii  is  burned  10  a  brown  or  n  black.  An
tXfm  of  furfiirol  sfWfi  an  oranK?  color.     Oxiiliiinn  bodici  prevent  Ihe  reaclion.
