678 
Methyl-Orange 
5  Am.  Jour,  Pharm. 
I       Oct.,  1921. 
The  two  formulas  given  above  if  calculated  to  a  common  basis 
will  not  agree ;  several  other  mixtures  were  made : 
Methyl  Indigo 
Orange.  Carmine.  Water. 
A  1. 000  Gm.  3.6  Gm.  1000  Cc. 
B  1-333  Gm.  4.0  Gm.  1000  Cc. 
C  1. 000  Gm.  2.5  Gm.  1000  Cc. 
D  (Kirschnick)  1.000  Gm.  3.0  Gm.  1000  Cc. 
Wilckes  0.8133  Gm.  3.0  Gm.  1000  Cc, 
0.2  cc.  of  D  diluted  to  100  cc.  will  duplicate  the  strength  recom- 
mended by  Kirschnick.  The  first  four  solutions  (C  and  D  prefer- 
entially) were  used  for  experimental  purposes  and  were  found  to 
give  uniform  results  in  titrations  with  tenth-normal  volumetric  solu- 
tions if  the  following  details  were  observed: 
Dilute  two  portions  of  0.2  cc.  indicator  with  100  cc.  of  water 
and  add  to  the  green  or  greenish-yellow  solutions  just  enough  acid 
volumetric  solution  to  discharge  the  yellow  or  green  color  without 
producing  a  red  or  violet  color;  should  the  latter  color  show  add 
enough  alkali  to  discharge  it.  The  object  is  to  produce  a  "neutral 
tint"  showing  neither  alkalinity  nor  acidity;  disregard  the  volumetric 
solutions  necessary  to  accomplish  this. 
Reserve  one  of  these  solutions  and  to  the  other  add  the  sub- 
stance to  be  titrated;  a  violet  or  purplish  color  indicates  an  acid 
substance,  a  yellow  or  green  color  indicates  an  alkaline  substance. 
Titrate  with  an  alkali  or  an  acid  volumetric  solution,  as  the  case  may 
require,  until  the  color  matches  that  of  the  reserved  solution.  It  is 
next  possible  to  add  to  the  reserved  solution  another  portion  of  the 
substance  to  be  titrated  and  check  this  against  the  previously  titrated 
portion.  The  titrated  solution  will  respond  by  color  change  with  a 
single  drop  of  acid  or  alkali  volumetric  solution. 
A  modification  of  this  method  was  tried  by  taking  in  duplicate, 
10  cc.  water,  0.05  cc.  indicator,  then  traces  of  acid  volumetric  solu- 
tion to  yield  the  neutral  tint  (which  in  this  case  is  colorless)  ;  next 
add  to  one  of  the  solutions  the  substance  to  be  determined  and  titrate 
with  acid  or  alkali  volumetric  solution  to  reproduce  the  neutral  tint. 
As  only  a  few  titrations  were  made  by  this  modification,  preference 
is  given  to  the  first  method. 
The  following  substances  were  titrated  in  the  course  of  the 
above  work :  Sulphuric  and  phosporic  acids,  sodium  borate*  carbon- 
