Am.  Jour.  Pharru. 
August,  1898. 
}     Valuation  of  Crude  Carbolic  Acid. 
377 
cresols  and  calculate  from  the  volume  of  bromine  solution  con- 
sumed their  approximate  percentages. 
The  writer  recommends  to  proceed  in  the  assay  as  follows :  Place 
I  gramme  of  the  sample  into  a  graduated  100  c.c.  flask,  nearly  fill  with 
water  and  shake  briskly  for  a  few  minutes.  Then  fill  to  the  mark 
with  water  and  mix  thoroughly.  Measure  2  c.c.  (=  o-02  gramme  of 
the  sample)  into  a  glass-stoppered  ioo  c.c.  flask,  excluding  undissolved 
matter,  by  filtration,  if  necessary.  Add  io  c.c.  of  water,  12  c.c.  of 
decinormal  bromine  solution  and  2  c.c.  of  hydrochloric  acid.  Stopper 
at  once  securely  and  shake  the  mixture  occasionally  during  a  half 
hour.  Then  add  2  c.c.  of  potassium  iodide  test-solution  in  such  a 
manner  as  to  avoid  loss  of  bromine  vapor  and  quickly  re-insert  the 
stopper.  Shake  thoroughly  and  add  decinormal  thiosulphate  solu- 
tion until  the  solution  is  decolorized.  If  the  sample  contains  cresols 
in  considerable  quantity,  the  solution  will  become  yellow  again 
after  standing  a  short  time,  probably  due  to  the  gradual  breaking 
up  of  an  addition-product  of  tri-brom-cresol  and  bromine  or  iodine. 
This  may  be  hastened  by  active  shaking  after  each  addition  of 
thiosulphate  to  the  decolorizing  point,  and  must  be  continued  until 
the  solution  remains  colorless  after  prolonged  shaking.  The  num- 
ber of  cubic  centimeters  required,  deducted  from  12,  gives  the 
number  of  cubic  centimeters  of  decinormal  bromine  solution  con- 
sumed by  o-o2  gramme  of  the  sample. 
The  following  short  table  will  assist  in  calculating  the  result  of 
the  titration.  It  gives  the  volume  of  decinormal  bromine  solution 
required  for  0-02  gramme  of  samples  containing  85  percent,  of  phenol 
and  cresols,  in  different  ratios,  and  10  per  cent,  of  tar-oils,  the 
bromine  absorbed  by  these  being  included  : 
Chiefly  phenol  iro  c.c. 
Phenol,  %\  cresol,  X  •  10*65  " 
The  quantity  of  the  still  higer  homologues  of  the  phenols  likely 
to  be  present  is  usually  too  small  to  make  it  necessary  to  consider 
them  in  the  calculations  for  such  rough  estimations. 
An  example  will  best  illustrate  the  calculation  of  results.  The 
appearance  of  the  precipitate  indicates  phenol  and  cresols  to  be 
present  in  about  equal  quantities,  and  10-7  c.c.  of  decinormal  bromine 
"  X; 
Chiefly  cresol 
10-3 
9'95  l! 
9-6  " 
