Xriri^iS:}       Purified  Cresol  {Cresylic  Acid).  249 
names,  is  inapplicable  for  use  as  a  serum  preservative  because  of 
three  specific  reasons,  all  of  which  are  interrelated,  namely : 
1.  Incomplete  solubility. 
2.  Disagreeable  odor. 
3.  Color. 
Incomplete  solubility  is  due  to  the  presence  of  one  or  more  of 
three  substances,  naphthalene,  colored  compounds  formed  appar- 
ently at  the  expense  of  the  cresols,  and  phenols  of  higher  boiling 
point  and  less  solubility  than  the  cresols. 
The  disagreeable  odor  is  largely  due  to  pyridine  and  partly  to 
the  naphthalene  which  have  been  incompletely  separated  in  pre- 
paring the  crude  phenol. 
The  origin  of  the  color  which  appears  in  cresol  and  phenol  is 
more  or  less  uncertain.  It  is  probably  not  always  due  to  the  same 
cause,  but  may  in  some  cases  be  due  to  impurities  in  the  cresol,  and 
in  others,  to  incidental  conditions,  such  as  the  effect  of  light  or  air 
or  the  action  of  alkali  from  the  glass  container. 
It  is  said  that  the  germicidal  value  of  a  highly  colored  lot  is 
greater  than  that  of  a  clear  straw-colored  sample.  This,  however, 
is  probably  a  hastily  drawn  conclusion  from  insufficient  evidence,, 
since  different  lots  are  found  to  differ  much  more  than  a  water- 
white  and  a  colored  sample  from  the  same  lot.  Redistillation  cor- 
rects the  color  and  can  improve  the  solubility  and  odor,  but  not  to 
a  sufficient  extent. 
The  development  of  color  appears  to  be  a  property  not  only  of 
cresols  but  also  of  pure  phenol  and  no  method  has  been  devised  by 
which  such  a  change  can  be  entirely  prevented.  The  coloring  mat- 
ter appears  to  be  a  new  constituent  and  to  have  properties  entirely 
different  from  those  of  the  original  cresols.  It  remains  behind  on 
redistillation,  but  further  quantities  form  so  that  only  the  freshly 
distilled  material  is  entirely  colorless. 
Gibbs^  ascribes  the  development  of  color  by  the  action  of  sun- 
light to  a  labile  hydrogen  atom  and  describes  experiments  with  the 
three  cresols  in  which  coloration  occurred  in  varying  times  with  the 
different  ones,  but  all  were  affected  in  the  same  way. 
This,  however,  does  not  explain  the  immediate  cause  of  this 
coloration.  A  sample  of  a  freshly  redistilled  lot  was  set  in  the  sun- 
light and  another  was  kept  in  an  amber  bottle  in  the  dark.  The 
first,  after  three  months,  was  very  slightly  tinged  with  pink,  the 
2  /.  Am.  Chem.  Soc,  34:  1190,  1912. 
