Am.  Jour.  Pharm. 
February,  1898. 
Testing  of  Formaldehyde. 
89 
Acetone. — 3  grammes  of  formaldehyde  solution,  25  c.c.  of  _  soda 
solution,  and  0  5  c.c.  of  pure  acetone  were  heated  under  pressure  in 
boiling  water  for  45  minutes.  A  duplicate  assay,  omitting  the 
acetone,  was  made  under  the  same  conditions.  In  the  mixture 
containing  the  acetone  a  white,  flocculent  precipitate  formed  on 
heating,  and  titration  with  sulphuric  acid  indicated  that  not  more 
than  one-third  of  the  theoretical  amount  of  soda  had  been  used  up. 
The  duplicate  containing  no  acetone  gave  normal  figures.  No 
attempt  has  yet  been  made  to  ascertain  the  composition  of  the  pre- 
cipitate and  the  cause  of  its  formation. 
Methyl  Alcohol — To  20  c.c.  of  a  dilute  aqueous  solution  of  pure 
formaldehyde,  1  c.c.  of  commercial  methyl  alcohol  was  added  and 
the  mixture  heated  with  soda  solution,  as  described  in  the  acetone 
experiment.  The  solution  was  assayed  under  the  same  conditions 
without  addition  of  methyl  alcohol  : 
Repeated  with  pure  methyl  alcohol,  0-5  c.c.  of  this  was  added  to 
2-25  grammes  of  a  concentrated  solution  of  pure  formaldehyde: 
Per  cent. 
No  explanation  can  be  made  at  present  for  the  lowering  of  the 
result  by  the  presence  of  methyl  alcohol. 
The  chief  disadvantages  of  the  fixed-alkali  method  are  interfer- 
ence by  acetone  and  methyl  alcohol  and  risk  of  explosion  when 
heating  under  pressure.  It  is  also  subject  to  some  variation  in  the 
results — noticed  with  one  sample  only — the  causes  of  which  cannot 
be  satisfactorily  explained  at  present. 
Ammonia  Method. — First  proposed  by  Legler  (Berichte,  vol.  XVI., 
p.  1333)  and  based  on  the  reaction  of  free  ammonia  and  formalde- 
hyde to  form  hexamethylene-tetramine  : 
A  normal  ammonia  solution  is  usually  recommended,  while  the 
decinormal  is  preferred  by  others.  As  the  use  of  the  latter  necessi- 
tates weighing  or  measuring  very  minute  quantities  of  formalde- 
hyde, or  else  diluting  a  larger  quantity  and  taking  an  aliquot  part 
Per  cent. 
Without  methyl  alcohol 
With 
4-65,  4-65,  471 
4'38,  4o5 
Without  methyl  alcohol 
With 
6  CH20  -  4  NH3  =  N4  (CH2)6  +  6  H2Q. 
