276  Amy  I  Nitrite  and  Nitrous  Ether.  {Am 
the  solution.  While  it  is  possible  that,  by  carefully  maintaining  all 
conditions  of  time,  dilution,  surface  exposure,  etc.,  results  agreeing 
approximately  with  those  of  the  gasometric  method  may  be  obtained, 
it  is  the  writer's  experience  that  parallel  experiments  by  both  meth- 
ods, and  considerable  practice  are  required  to  accomplish  this. 
The  late  Prof.  Charles  O.  Curtman  published  (Ph.  Rundschau, 
1892,  p.  156)  a  modification  of  Eykman's  gasometric  method/which 
depends  upon  the  following  reaction : 
2C2H6N02  +  2  FeS04  +  H2S04  =  N202  +  2C2H5OH  +  Fe2(S04)3. 
The  modification  consists  in  expelling  the  nitric  oxide  by  boiling, 
and  estimating  the  quantity  of  ferric  salt  formed  in  the  reaction,  by 
adding  potassium  iodide  and  titrating  the  liberated  iodine  with  thio- 
sulphate.  Dr.  Curtman  proceeded  by  measuring  into  a  100  c.c. 
flask  10  c.c.  of  a  normal  solution  of  ferrous  ammonium  sulphate, 
10  c.c.  of  normal  sulphuric  acid  and  5  c.c.  of  the  spirit  to  be  tested, 
and  allowed  the  mixture  to  stand  a  half  hour,  after  stoppering  the 
flask  carefully  with  a  rubber  or  cork  stopper.  The  stopper  was  then 
loosened,  but  not  taken  off,  and  the  contents  of  the  flask  heated 
rapidly  to  boiling,  which  was  continued  until  all  nitric  oxide  had 
been  expelled  from  the  flask,  the  stopper  being  removed  toward 
the  end.  The  contents  of  the  flask  were  then  cooled  to  400  C,  10  c.c. 
of  normal  potassium  iodide  solution  added,  the  solution  kept  at 
400  C.  for  one  hour,  and  the  iodine  titrated  after  cooling. 
Dr.  Curtman  did  not  claim  great  accuracy  for  this  method,  and 
gave  preference  to  Allen's  gasometric  method.  Following  the  direc- 
tions above  given,  the  present  writer  obtained  4-03,  3-38  and  4-07 
per  cent.,  against  4-59  by  nitrometer.  After  several  unsuccessful 
attempts,  475  per  cent,  was  obtained  in  duplicate  estimations,  by 
doubling  the  time  allowed  for  the  reaction  in  the  first  part  of  the 
process.  Aside  from  the  fact  that  it  requires  considerable  care  and 
attention,  this  method  is  subject  to  several  sources  of  error  that  are 
likely  to  discourage  its  use.  The  nitric  oxide  acts  as  a  carrier  of 
oxygen  and  raises  the  result,  though  to  a  less  extent  than  is  the 
case  with  the  first  method  discussed.  This  is  evidenced  by  the  fact 
that  the  results  were  always  much  too  high  when  the  mixtures  of 
ferrous  sulphate,  sulphuric  acid  and  spirit  were  allowed  to  stand 
much  longer  than  one  hour  before  expelling  the  nitric  oxide.  The 
liability  of  ferrous  salts  to  contain  fern'^r  salts  is  also  apt  to  cause 
error  and  inconvenience. 
