250  Purified  Cresol  {Cresylic  Add).       l^"^' ^^pril^igTo. 
other  was  decidedly  reddened.  This  is  not  an  isolated  case  but 
was  a  careful  demonstration  of  what  frequently  occurs  in  practice 
with  large  lots.  Sufficient  observations  have  not  been  made  to 
arrive  at  a  theory  as  to  the  cause  or  causes  of  the  change  and  no 
method  has  consistently  prevented  its  recurrence. 
The  disagreeable  odor  is  due  to  pyridine  and  naphthalene  which 
one  would  naturally  think  were  eliminated  in  the  process  of  sep- 
arating the  cresols  from  the  creosote  oil.  In  this  process  the  acid 
constituents  of  the  oil  are  combined  with  an  alkali  such  as  caustic 
soda  or  lime,  and  in  this  form  should  be  readily  separated  from 
the  neutral  and  basic  substances.  In  fact  only  a  very  small  per- 
centage of  these  bodies  remain  with  the  cresols  and  are  dissolved 
with  it  when  its  alkaline  combination  is  broken  up,  as  it  is  in  prac- 
tice, with  carbonic  or  sulphuric  acid.  The  odor  of  crude  carbolic 
acid  is  not  distinctly  like  either  impurity,  since  the  natural  odor 
of  the  cresols  masks  the  others  until  they  are  unrecognizable.  Dis- 
tillation carries  these  impurities  over  and  little  improvement  can  be 
accomplished  by  this  step  as  the  sole  purifying  process. 
Nevin  and  Mann^  depended  on  separation  by  redistillation  to 
obtain  the  proper  fraction  but  this,  as  noted  above,  while  removing 
the  colored  and  some  of  the  insoluble  impurities,  fails  to  remove 
pyridine  and  naphthalene,  which  are  responsible  for  the  odor.  While 
this  odor  is  perhaps  negligible,  it  is  easy  to  detect  the  difference 
between  two  lots  of  cresol,  one  purified  to  remove  the  odorous 
impurities,  as  will  be  described  later,  and  the  other  purified  by 
redistillation  only. 
In  my  experiments  an  attempt  was  made  to  study  the  sodium 
cresylate  compound  when  prepared  in  molecular  proportions.  In 
concentrated  solution  no  observable  separation  takes  place  to  indi- 
cate that  purification  by  this  means  is  feasible,  but  on  further  dilu- 
tion the  naphthalene  crystallizes  out  in  a  well-recognized  form  and 
often  in  considerable  quantities.  This  can  be  filtered  out,  but  on 
again  recovering  the  cresols  no  material  improvement  in  odor  ,  re- 
sults, because  the  naphthalene  is  the  less  objectionable  of  the  two. 
My  next  experiments  were  carried  out  having  in  mind  the  ex- 
amination of  sodium  cresylate  in  solid  form  to  see  if  impurities  could 
be  detected,  identified,  and  removed  by  tests  applied  to  the  dried 
or  crystallized  material. 
3  /.  Am.  Chem.  Soc,  39:  2752,  1917. 
