4/6 
Laboratory  Notes. 
/Am.  Jour.  Pharm. 
t     October,  1904. 
of  bromine  v.  s.  after  the  addition  of  potassium  iodide  with  sodium 
thiosulphate  v.  s.  with  starch  as  indicator,  the  presence  of  the  pre- 
cipitated tri-brom.phenol  interferes  somewhat  with  the  end-reaction  ; 
frequently  in  old  phenol  solutions  the  tri-brom-phenol  possesses  a 
bluish  color  which  is  not  removable  by  an  excess  of  sodium  thio- 
sulphate v.  s.  and  which  makes  the  end-reaction  difficult.  To  over- 
come the  difficulties  mentioned  I  have  recently  been  using  a  small 
quantity  of  chloroform  (i  c.c.  is  sufficient),  which  is  added  after 
most  of  the  brown  color  has  been  discharged  by  the  addition  of  the 
sodium  thiosulphate  v.  s. ;  the  chloroform  will  dissolve  the  tri-brom- 
phenol  and  allow  a  very  sharp  end-reaction. 
To  those  accustomed  to  making  iodine-titrations  in  presence  of 
chloroform  it  is  needless  to  recall  that  the  chloroform  will  dissolve 
and  retain  part  of  the  iodine  in  solution,  and  that  the  sodium  thio- 
sulphate v.  s.  must  be  added  as  long  as  a  blue  color  (due  to  the 
starch-iodide)  is  imparted  to  the  aqueous  supernatant  liquid  upon 
thorough  agitation  with  the  chloroform  ;  in  fact,  it  is  possible  to 
titrate  without  the  use  of  starch-indicator,  the  end-reaction  being 
known  by  a  colorless  aqueous  solution  and  the  chloroform  free  from 
any  tinge  of  pink  which  is  due  to  traces  of  iodine. 
Any  error  caused  by  reaction  between  iodine  and  the  chloroform 
can  be  compensated  for  by  titrating  the  bromine  v.  s.  with  the  addi- 
tion of  chloroform  under  precisely  the  same  conditions  as  exist  in 
this  modified  phenol  determination. 
Starch  Indicator. — The  deterioration  of  starch  solutions  has  been 
the  cause  of  much  annoyance  to  those  interested  in  analytical  work. 
A  large  number  of  substances  have  been  suggested  as  preservatives 
for  starch  solutions,  but  none  of  these  are  altogether  satisfactory,  and 
frequently  the  preservative  is  of  such  chemical  character  that  the 
starch  solution  cannot  be  used  for  both  qualitative  and  quantitative 
work. 
Something  over  a  year  ago,  as  the  result  of  a  series  of  experiments 
which  proved  the  above  statements,  the  writer  was  led  to  try  the 
action  of  oil  of  cassia  as  a  preservative,  influenced  by  a  vague  rec- 
ollection of  having  seen  some  years  ago  a  statement  to  the  effect 
that  oil  of  cassia  had  a  remarkable  preservative  action  upon  some 
of  the  carbohydrates. 
The  experiment  was  a  decided  success,  so  that  the  solution  made 
up  in  quantities  of  I  liter  could  be  used  to  the  last  drop.  The  starch 
