232 
Hydrogen  Dioxide. 
Am.  Jour.  Pharru. 
May,  159S. 
Substances  Added. 
Permanganate 
Method, 
Titrimetric. 
Hypochlorite 
Method. 
Thiosulphate 
Glvcerin,  5  p.c  
io'55;  10-45 
io"2;  10*25 
IC25;  I0'25 
Boroglvcerin,  5  p.c  
10-45;  Io'5 
10-15;  10*05 
10:25;  IC3 
Boric  acid,  5  p.c  
IC3;  IC25 
io'3 ;  io"2 
1C3;  io"25 
Boric  acid,  20  p.c  
10*3;  io"3 
io'i;  io'i5 
10  3,   10  35 
Salic3"lic  acid,  o-2  p.c.   
11*3;  ir'5 
9"6;  9*7 
10*3;  io"3 
Salicylic  acid,  2  p.c  
9'55;  9*4 
10-3;  10-4 
10-45:  10-4 
10*15;  1015 
10-45;  10-4 
Salol,  saturated  solution*  
10-25;  10-25 
100;  9-85 
IO-2;  IO"2 
Acetanilid,  0*5  p.c  
10-3;  10-3 
io-i;  io'2 
10-25;  10-25 
10-35;  10-35 
10*65;  107 
10-25;  10-25 
*  Prepared  by  diluting  13-35  c.c.  of  H2Oo  solution  with  a  cold,  aqueous,  saturated  solution  of 
salol  to  100  c.c." 
These  results  show  that  the  accuracy  of  the  titrimetric  permanga- 
nate method  is  affected  slightly  by  the  presence  of  moderate  quanti- 
ties of  glycerin  or  boroglycerin,  but  that  in  the  presence  of  the 
quantities  that  would  be  added  to  the  solutions  by  manufacturers, 
which  would  hardly  exceed  I  per  cent.,  the  difference  in  result 
would  not  be  noticeable.  In  presence  of  salicylic  acid,  however,  the 
method  is  worthless.  There  is  evidence  also,  that  ether  is  not 
entirely  without  influence.  It  may  be  stated,  then,  as  a  generaliza- 
tion, that  in  presence  of  organic  substances,  titration  with  potassium 
permanganate  cannot  be  depended  upon  to  always  give  sufficiently 
accurate  results  for  pharmacopceial  purposes. 
With  the  hypochlorite  method  there  is  a  tendency  toward  low- 
results,  most  marked  in  presence  of  salicylic  acid.  The  presence  of 
ether  introduces  an  error,  which  is  probably  due  largely  to  the 
increased  vapor  tension.  While  the  inaccuracies  of  some  of  the 
results  of  this  method  may  be  partially  attributed  to  a  neglect  to 
make  corrections  for  variation  in  barometric  pressure  and  for  the 
tension  of  water  vapor,  it  was  proven  by  parallel  estimations  during 
the  same  atmospheric  pressure,  that  some  of  the  added  substances 
without  doubt  exert  an  influence  on  the  volume  of  gas  liberated. 
This  method,  then,  is  also  unreliable  in  presence  of  organic  matter, 
but  less  so  than  the  permanganate  methods. 
The  accuracy  of  the  thiosulphate  method  is  practically  unaffected 
by  the  addition  of  any  of  the  substances  given  in  the  table.  The 
differences  in  the  results  are  probably  due  as  much  to  variation  in 
