32 
Tests  for  Carbolic  Acid,  etc. 
Am.  Jour.  Pharm 
Jan.,  1879. 
tube  with  a  freezing  mixture  (or  by  wrapping  filter  paper  round  it  and 
dropping  ether  on  the  outside),  when  carbolic  acid  crystallizes  out. 
Absolute  carbolic  acid  is  permanently  soluble  in  about  ten  measures 
of  petroleum  spirit  at  I5'5C.  (=6o°F.).  The  solubility  is  enormously 
increased  by  rise  of  temperature.  Hence  carbolic  acid  and  hot  petro- 
leum spirit  are  miscible  in  all  proportions.  On  the  other  hand,  by 
cooling  with  a  freezing  mixture  the  carbolic  acid  is  almost  wholly 
deposited. 
If  the  cooling  occurs  slowly  it  forms  a  heavy  liquid  layer  with  a 
portion  of  the  petroleum  spirit,  but  by  rapid  cooling  the  carbolic  acid 
is  deposited  in  long  crystalline  needles  which  render  the  liquids  semi- 
solid.1 
Hydrous  carbolic  acid  is  almost  insoluble  in  moderate  quantities  of 
cold  petroleum  spirit,  which  liquid  does  not  separate  the  contained 
water  from  it.  (Another  difference  between  benzol  and  petroleum 
spirit.)  Absolute  cresylic  acid  appears  to  be  miscible  with  petroleum, 
spirit  in  all  proportions. 
No  separation,  either  of  crystals  or  liquid,  occurs  by  exposing  a 
solution  of  one  measure  of  the  acid  in  three  of  petroleum  spirit  to  a 
freezing  mixture. 
When  hydrous  cresylic  acid  is  treated  with  cold  petroleum  spirit  the 
volume  of  the  former  increases  somewhat  by  dissolving  a  little  of  the 
spirit,  but  on  addition  of  a  greater  volume  of  petroleum  spirit  it  under- 
goes slight  solution.  It  is  only  very  sparingly  soluble  in  petroleum 
spirit,  requiring  upwards  of  twenty  volumes  for  complete  solution, 
when  the  water  separates.  Creasote  is  miscible  with  petroleum  spirit 
in  all  proportions. 
9.  Behavior  with  Glycerin  of  1*258  sp.gr. — Absolute  carbolic  acid 
is  miscible  with  Price's  glycerin  in  all  proportions.  A  mixture  of  one 
volume  of  carbolic  acid  with  one  of  glycerin  is  not  precipitated  on 
addition  of  three  volumes  of  water.  In  presence  of  25  per  cent,  of 
cresylic  acid  precipitation  occurs  on  adding  more  than  two  volumes  of 
water. 
1  Crystallized  carbolic  acid  may  be  used  for  distinguishing  between  coal-tar 
benzol  and  petroleum  spirit.  In  the  latter  it  is  sparingly  soluble,  and  is  re-depos- 
ited in  a  crystalline  state  by  rapid  cooling.  With  benzol  it  is  miscible  in 
all  proportions,  the  crystals  of  carbolic  acid  rapidly  melting.  A  solution  of  one  in 
three  deposits  no  crystals  by  rapid  cooling. 
