Am.  jour.  Pharm. |      Determination  of  Boric  Acid. 
January,   19 17.    J  J 
9 
changed  the  methyl  orange  from  the  distinctly  alkaline  yellow  color 
to  the  neutral  tint.  The  sharpness  of  this  color  change  with  methyl 
orange  seems  to  indicate  that  it  is  not  the  boric  acid  which  causes 
the  slow  color  change  noted. 
After  the  neutralization  of  the  solutions,  glycerin  was  added  and 
then  titrated  to  a  pink  color  with  phenolphthalein.  The  boric  acid 
calculated  from  these  titrations  averaged,  in  the  solutions  neutralized 
to  methyl  orange  0.2007  Gm.,  in  those  neutralized  to  methyl  red 
0.2001. 
When  glycerin  is  added  to  a  solution  containing  methyl  red  the 
indicator  changes  its  color  to  red  and  as  the  titration  proceeds  the  red 
color  fades  slowly,  the  point  at  which  the  indicator  is  half  trans- 
formed occurring  when  about  half  the  alkali  necessary  for  titration 
with  phenolphthalein  has  been  added. 
Titration  of  Boric  Acid  in  Solutions  Containing  Sodium 
Carbonate. 
Several  solutions  were  prepared  containing  in  each  1  Gm.  sodium 
carbonate  with  a  known  amount  of  boric  acid,  thus  simulating  the 
conditions  met  with  in  the  determination  of  boric  acid.  The  titra- 
tions were  carried  out  according  to  the  method  given  below.  The 
endpoints  obtained  with  methyl  red  in  the  neutralization  of  excess 
acid  were  as  sharp  as  usual  but  those  obtained  with  methyl  orange 
were,  as  the  author  had  noted  before,  indistinct.  Can  it  be  that 
the  endpoint  of  methyl  orange  is  affected  by  a  considerable  amount 
of  salts  in  the  solution  titrated?  The  results  of  these  titrations  are 
given  in  the  attached  table. 
Method. 
The  solution  was  carefully  neutralized  in  the  cold  with  normal 
sulfuric  acid  and  about  0.2  to  0.3  Cc.  added  in  excess,  the  beaker 
being  covered  with  a  watch  glass  meanwhile  to  avoid  loss  by  effer- 
vescence. The  solution  in  the  beaker,  still  covered  with  the  watch 
glass,  was  quickly  heated  to  boiling  and  boiled  about  1  minute.  In 
the  case  of  the  solutions  in  which  methyl  red  was  used  as  indicator, 
if  the  color  had  faded  and  become  alkaline,  normal  acid  was  added 
until  the  red  color  was  restored  and  the  boiling  continued  for  1 
minute.  The  solutions  were  then  cooled  to  20  to  25 0  and  neutralized 
with  tenth  normal  sodium  hydroxide  solution.  The  neutral  point 
with  methyl  orange  being  taken  as  that  point  where  a  clear  yellow 
