86  Testing  of  Formaldehyde.  {Af^ryPimm' 
TESTING  OF  FORMALDEHYDE. 
By  Carl  B.  Smith. 
Report  of  Research  Committee  DII.,  Committee  of  Revision  of  the  United 
States  Pharmacopoeia. 
The  rapidly  increasing  uses  of  formaldehyde  make  it  desirable 
that  standards  be  established  for  the  strength  and  purity  of  the 
commercial  products.  A  method  of  assay,  simple  and  rapid,  as  well 
as  reasonably  accurate,  is  needed  as  a  guide  for  manufacturer 
and  pharmacist,  as  also  tests  for  the  various  impurities  liable  to  be 
present,  and  reactions  to  establish  its  identity.  As  the  commercial 
solutions  vary  considerably  in  quality,  ready  means  should  be  at 
hand  for  controlling  the  quality  of  the  pharmacist's  supply. 
ASSAY  METHODS. 
A  method  of  assay,  to  be  generally  applicable,  must  not  be 
affected  in  accuracy  by  the  presence  of  ordinary  impurities  fre- 
quently contained  in  commercial  formaldehyde  solution,  such  as 
methyl  alcohol  and  acetone ;  neither  should  it  require  much  time 
and  attention  or  complicated  operations.  Of  the  number  of  methods 
which  have  been  published  within  recent  years,  the  principal  ones 
were  examined,  in  order  to  ascertain  which  of  them  approaches 
nearest  to  these  requirements,  with  the  results  stated  below  : 
Hydroxylamine  Method. — Proposed  by  Brochet  and  Cambier 
(Compt.  Rend.,  vol.  120,  p.  449,  and  Ztsch.  f.  Anal.  Chem.,  vol.  34, 
p.  623).  Based  on  the  reaction  of  hydroxylamine  hydrochloride 
and  formaldehyde,  with  the  liberation  of  hydrochloric  acid,  accord- 
ing to  the  following  equation  : 
NH2OH.HCl  +  H.COH  =  CH2N(OH)  +  HC1  -f  H20. 
The  formaldehyde  entered  into  combination  is  determined  by  the 
amount  of  acid  set  free. 
In  the  experiments  made  the  details  prescribed  by  the  authors 
were  followed,  except  that  —  soda  solution  was  used  for  titrating 
10 
n 
the  hydrochloric  acid  instead  of  _  borax  solution. 
10 
10  c.c.  of  a  solution  containing  0-0864  gramme  of  a  concentrated 
formaldehyde  solution  were  mixed  in  a  small  flask  with  10  c.c.  of  a 
2-5  per  cent,  solution  of  hydroxylamine  hydrochloride.  (The 
hydroxylamine  salt  is  about  5  times  the  amount  involved  in  the 
