470  Nvtc  oil  Assay  of  formaldr/iydc.        1^"™:  fij*'""'- 
-      '  (     OclolKM-,  1911. 
of  absolute  fonnakk'li\de  1)\  weii^lit.  Likewise.  Bach  man reports 
solution  of  formaldehyde  ranging  from  36.6  per  cent,  to  31.8  per 
cent.,  instead  of  the  minimum  of  37  per  cent,  as  required  by  the 
present  U.S. P.  Finally,  we  may  mention  in  this  connection  that  the 
formaldehyde  requirement  of  the  French  Pharmacopoeia  (1908)  and 
also  of  the  German  Pharmacopoeia  (1910)  is  only  35  ])er  cent,  by 
weight  (^f  absolute  formaldehyde.  (  )n  the  other  hand,  with  the 
exception  of  only  one  sample  (No.  ij,  all  contained  more  than  3O 
per  cent,  by  weight  of  absolute  formaldehyde.  Therefore,  bearing  in 
mind  the  comparative  difficulty  of  manufacturing  and  keeping  unal- 
tered solutions  of  formaldehyde  of  considerably  higher  concentration 
than  the  minimum  of  the  present  U.S. P. ;  and  also  that  by  making 
the  U.S. P.  requirement  more  in  harmony  with  these  latter  pharmaco- 
poeias and  with  what  seems  to  be  the  actual  condition  of  the  American 
market,  it  would  not  mean  that  the  purity  requirement  will  be  low- 
ered but  only  that  the  solution  will  be  just  a  little  less  concentrated; 
it  would  seem  advisable  that  the  formaldehyde  requirement,  in  the 
next  revision  of  the  U.S. P.,  be  changed  from  the  present  minimum 
of  37  per  cent,  to  a  minimum  of  36  per  cent,  by  weight  of  absolute 
formaldehyde.  Also  that  the  KCN  method  might  with  advantage 
be  substituted  for  the  present  H^Oo  method.  .  The  KCN  method, 
applied  to  U.S. P.  solution  of  formaldehyde,  may  be  carried  out 
as  follows : 
Transfer  0.5  c.c.  of  the  sample  of  Solution  of  Formaldehyde  to 
a  well-stoppered  Erlenmeyer  flask  of  about  150  c.c.  capacity  and 
determine  its  weight.  Add  to  it  immediately  100  c.c.  of  a  solution 
of  potassium  cyanide  of  a  strength  close  to  tenth-normal  (6.5  Gm. 
KCN  to  1000  c.c),  the  exact  strength  of  which  is  known.  Mix 
well,  and  add  to  a  mixture  of  40  c.c.  n/to  silver  nitrate  and  10  c.c. 
of  dilute  (10  per  cent.)  nitric  acid,  in  a  200  c.c.  measuring  flask. 
Wash  the  Erlenmeyer  flask,  adding  the  washings  to  the  silver  solu- 
tion, and  make  up  the  whole  to  200  c.c.  Shake  thoroughly,  filter 
through  a  dry  filter,  and  titrate  the  excess  of  silver  in  100  c.c.  of  the 
filtrate  by  means  of  n/io  ammonium  or  potassium  sulphocyanate, 
using  ferric  alum  as  indicator.  The  number  of  c.c.  of  n/io  sulpho- 
cyanate  found  to  require,  multiplied  by  2,  and  the  product  subtracted 
from  40,  will  give  the  equivalent  of  the  uncombined  KCN  in  c.c.  of 
Proc.  Minnesota  Pharm.  Ass.,  1907,  p.  41 ;  from  Bull.  No.  63,  Hyg.  Lab., 
U.  S.  Pub.  Health  &  Mar.  Hosp.  Serv.,  Wash.,  p.  295. 
