274  Amy  I  Nitrite  and  Nitrous  Ether.  {AmjJu°nue,;-if9h8arm- 
U.S. P.  method  of  assay,  and  by  the  necessity  of  either  purchasing  a 
special  apparatus,  a  nitrometer,  or  else  taking  the  trouble  to  impro- 
vise one  from  other  apparatus  at  hand.  Hence,  the  control  of 
the  strength  of  these  preparations,  under  present  conditions,  is 
restricted  almost  entirely  to  manufacturing  and  analytical  labora- 
tories. It  is  a  desideratum,  therefore,  for  the  pharmacist  to  be  in 
possession  of  a  method  of  valuation  that  does  not  require  special 
apparatus  and,  in  other  respects,  is  adapted  to  the  requirements  of 
the  dispensing  pharmacist.  In  a  search  for  such  a  method,  the 
writer  has  examined,  without  success,  those  of  the  older  existing 
methods  of  titration  that  appeared  most  promising,  but  has  suc- 
ceeded in  adapting  a  new  method,  very  recently  proposed  for  alkali 
nitrites,  to  the  estimation  of  ethyl  and  amyl  nitrite.  It  is  readily 
applied  by  any  one  who  is  acquainted  with  the  rudiments  of  volu- 
metric analysis,  and  requires  only  the  ordinary  apparatus  employed 
in  such  work.  Experiments  seem  to  show  also,  that  it  is  capable  of 
greater  accuracy  than  the  gasometric  method,  which  is  in  general 
use  at  present.  Before  describing  it  fully,  an  account  of  the  experi- 
ments made  in  connection  with  the  other  methods  tried  will  be  given. 
The  U.S.P.  method  is  essentially  that  of  A.  H.  Allen  (Ph.  J.  Tr., 
1885,  ser.  3,  vol.  15,  p.  674),  who  makes  use  of  the  following  reac- 
tion, by  measuring  the  nitric  oxide  formed  : 
2C2H5N02  -f-  2KI  +  2H2S04  =  2C2H5OH  +  N202  +  I2  +  2KHSO,. 
This  reaction  had  previously  been  employed  by  D.  B.  Dott,  who 
recommended  titrating  the  liberated  iodine  with  thiosulphate.  This 
procedure  was  soon  found  unreliable  by  Allen  and  others,  and  was 
superseded  by  Allen's  gasometric  modification.  The  cause  of  inac- 
curacy is  the  instant  oxidation  of  nitric  oxide  (N202)  on  contact  with 
air,  to  nitrogen  tetroxide  (N2Od),  which  continues  to  set  free  iodine 
from  the  hydriodic  acid  in  solution,  and  causes  the  result  to  be  much 
too  high.  Mr.  Dott  then  proposed  a  modification  (Ph.  J.  Tr.,  (3)  vol. 
15,  p.  697),  in  which  air  was  to  be  excluded  by  generating  carbon 
dioxide  within  the  vessel  in  which  the  operation  was  performed,  but 
this  also  failed  to  find  the  approval  of  others.  It  has  further  been 
recommended  to  conduct  the  operation  in  an  atmosphere  of  coal-gas, 
and  accurate  results  have  been  reported  by  the  employment  of  this, 
but  the  necessity  of  having  a  specially  constructed  apparatus  and 
the  care  and  practical  skill  required  to  obtain  serviceable  results 
