n8 
Crude  Carbolic  Acid. 
f  Am.  Jour.  Pharm 
1     March,  1894. 
if  not  better,  disinfecting  properties  than  phenol,  it  does  not  seem 
necessary  to  determine  any  other  point  than  the  total  per  cent,  of 
acid  they  contain.  No  simpler  method  can  be  devised  than  the 
well  known  one  of  shaking  a  certain  quantity  of  the  material  in  a 
graduated  vessel,  with  weak  caustic  soda,  and  noting  the  decrease  in 
volume.  To  verify  the  result  the  soda  solution  can  be  acidified  and 
the  tar  acids  measured.  The  amount  liberated  is  always  less  than 
that  indicated  by  the  decrease  of  the  volume  of  oil,  owing  to  the 
solubility  of  the  acid  in  the  salt  solution. 
For  this  test  I  would  recommend  a  ioo  cc.  burette,  divided  in 
tenths,  and  furnished  with  a  glass  stop-cock.  It  is  filled  to  the  50 
cc.  mark  with  10  per  cent,  of  caustic  soda  solution;  25  or  50  cc. 
of  the  acid  to  be  tested  is  then  added,  the  burette  closed  with  a 
cork  and  well  shaken.  On  allowing  to  stand,  the  decrease  in  the 
volume  of  oil  is  readily  measured ;  50  cc.  soda  of  the  strength 
indicated  is  sufficient  to  saturate  12  cc.  of  100  per  cent.  acid.  If  it 
is  necessary  to  add  more  soda  the  already  saturated  solution  can  be 
readily  drawn  from  the  burette  and  another  50  cc.  added. 
Frequently  the  percentage  of  naphthaline  in  low  grade  acids  is  so 
great  that  it  separates  from  the  liquid  as  soon  as  the  acids  are 
removed ;  as  this  prevents  an  accurate  reading,  it  is  necessary  to  add 
10  to  15  cc.  of  benzol  to  dissolve  the  deposit. 
In  some  cases  the  acids  are  contaminated  with  tarry  or  resinous 
bodies,  which  dissolve  in  the  caustic  soda,  rendering  the  solution  so 
dark  that  it  is  impossible  to  see  the  line  separating  the  two  liquids. 
In  this  case  it  is  advisable  to  distil  another  25  cc.  portion  nearly  to 
dryness  in  a  small  flask,  considering  the  distillate  as  25  cc,  and 
repeating  the  test.  The  entire  operation  requires  but  a  few  minutes, 
and  the  results  of  many  hundred  trials  show  it  to  be  accurate  enough, 
for  general  purposes. 
A  mixture  of  equal  parts  of  heavy  oil  and  cresylic  acid  was  made, 
and  tested  by  the  above  method.  The  contraction  showed  49^ 
per  cent,  of  acid  present,  the  liberated  phenols  gave  49  per  cent. 
The  same  mixture  tested  by  Setter's  lime  method,  gave  only  22  per 
cent,  every  precaution  being  taken  to  insure  a  good  result. 
Another  mixture  prepared  with  25  per  cent,  of  acid,  gave  24^ 
per  cent,  by  extraction,  and  24  per  cent,  of  phenols  set  free.  The 
lime  method  gave  but  6  per  cent. 
The  Pharmacopoeia  requires  that  50  volumes  of  a  crude  acid 
