Am.  Jour.  Pharm.  ) 
January,  1910.  j 
Ammonium  Benzoate. 
15 
the  gradual  loss  of  ammonia,  the  inferiority  of  a  given  sample  due 
to  this  cause  is  not;  detected  as  readily  by  the  formaldehyde  as  by 
the  distillation  method  of  analysis.  This  fact  is  very  forcibly  illus- 
trated by  the  titration  of  the  mixture  of  ammonium  benzoate  and 
benzoic  acid  shown  above.  In  this  case,  although  there  was  present 
20  per  cent,  of  free  benzoic  acid,  there  was  obtained  a  difference  of 
only  1. 1 5  c.c.  (37. 1-35.95)  of  0.1  N  NaOH  from  the  amount  theo- 
retically required  for  pure  ammonium  benzoate.  Thus,  by  the  for- 
maldehyde method  each  0.115  c.c.  of  0.1  N  NaOH,  when  0.5  Gm 
samples  are  employed,  corresponds  to  2.0  per  cent,  of  free  benzoic 
acid.  By  referring  to  Table  I  it  will  be  found  by  calculation  that, 
on  the  basis  of  the  ammonia  determination,  the  presence  of  2.0 
TABLE  II. 
ANALYTICAL   RESULTS    UPON    AMMONIUM    BENZOATE   SAMPLES    OBTAINED  BY 
THE  FORMALDEHYDE  METHOD. 
Sample  No.   j    Gms.  used 
C.c.  neutralized 
40  per  cent. 
C.c.  0.1  NaOH  required 
formaldehyde  j  Before  boUing 
After  boiling 
Calc.  per  cent. 
C6H6C00NH4 
222 
0.25 
1 .0 
222 
0.25 
3-° 
224 
0.50 
6.0 
223 
0.50 
8.0 
220 
0.50 
10. 0 
Mixture  * 
0.50 
6.0 
17-1  i 
17.85 
35-45 
35-45 
35-55 
36.7 
17-65 
17-95 
35-95 
35-  95 
36-  °5 
37-  i 
98.2 
99-9 
100.0 
100.0 
100.3 
103.2 
*  Mixture  =  o.4  Gm.  No.  224  +  0.1  Gm.  C6H6COOH,  i.e.,  20  per  cent. 
C6H6COOH. 
per  cent,  free  benzoic  acid  is  indicated  by  a  difference  of  0.74  c.c. 
of  0.1  N  H2S04  from  the  amount  theoretically  required  for  pure 
ammonium  benzoate.  The  explanation  of  this  advantage  of  the 
distillation  over  the  formaldehyde  method  in  the  case  of  ammonium 
benzoate  is  that  a  given  difference  between  the  composition  of  two 
samples  is  a  larger  percentage  of  the  ammonia  than  of  the  benzoic 
acid  present,  and  therefore  shows  itself  in  nearly  the  ratio  of  the 
amounts  of  these  two  constituents  in  the  compound. 
Stability  of  Ammonium  Benzoate  in  the  Air. — Although  it  is 
stated  in  the  Pharmacopoeia  that  the  salt  gradually  loses  ammonia 
when  exposed  to  the  air,  the  observations  which  we  have  made  indi- 
cate that  such  a  decomposition  is  very  slight  and  need  not  be  feared 
with  the  use  of  ordinary  precautions  for  protecting  the  sample, 
