3o8 
Spirit  of  Nitrous  Ether. 
Am.  Jour.  Pharm. 
June,  1897. 
10  c.c.  of  potassium  iodide  test  solution.  The  mixture  was  occa- 
sionally agitated  during  ten  or  fifteen  minutes,  a  few  drops  of  starch 
test  solution  added,  and  the  mixture  titrated  with  decinormal  sodium 
thiosulphate  volumetric  solution,  until  the  bluish-green  color  was 
discharged.  The  mixture  afterwards  assumed  a  dark  color ;  but 
if  the  time  of  maceration  does  not  exceed  fifteen  minutes,  the  num- 
ber of  cubic  centimeters  required  to  first  discharge  the  color  will 
give  nearly  or  quite  as  accurate  results  as  the  nitrometer.  Prof. 
Walker  also  said :  "  While  the  titration  process  may  not  be  quite  as 
accurate  in  its  figures  as  the  modified  Allen  method,  it  involves 
much  less  expense,  and  the  results  are  sufficiently  accurate  for  prac- 
tical purposes."  This  last  claim  Prof.  Walker  seemed  to  have  sub- 
stantiated by  the  figures  of  a  table  which  he  gave  to  show  the 
results  of  the  assay  of  ten  samples  by  the  two  methods. 
On  January  25,  1896,  the  same  journal  published  a  letter  from 
Mr.  Peter  MacEvvan,  of  London,  England,  in  which  that  gentleman 
directed  attention  to  the  fact  that  the  method  proposed  by  Professor 
Walker  had  been  suggested  by  Mr.  D.  B.  Dott  a  dozen  years  ago, 
and  had  to  be  abandoned  on  account  of  the  fallacious  results,  for 
whenever  the  nitric  oxide  liberated  by  decomposition  of  the  ethyl 
nitrite  comes  in  contact  with  the  air  of  the  flask,  nitrogen  tetroxide 
is  formed.  This  at  once  decomposes  more  of  the  alkaline  iodide ; 
indeed,  decomposition  might  go  on  indefinitely  if  the  supply  of  air 
and  iodide  were  large  enough.  Mr.  Dott  endeavored  to  obviate 
this  objection  by  various  means,  such  as  working  with  an  open  dish 
in  which  carbon  dioxide  was  simultaneously  generated,  but  with 
modified  success.  It  was  his  knowledge  of  the  difficulties  of  this 
method  which  led  Mr.  A.  H.  Allen  to  effect  the  reaction  in  an  air- 
free  space  and  estimate  the  nitric  oxide  instead  of  the  iodine;  the 
method  was  adopted  by  many  chemists,  and  simultaneously  indirect 
estimation  through  the  iodine  factor  was  deservedly  forgotten.  A 
man  who  knows  all  the  worries  of  the  latter  process  may  get  fairly 
accurate  results,  but  the  novice  or  careless  worker  may  return  a  3 
per  cent,  ethyl  nitrite  spirit  as  containing  anything  between  that 
and,  say,  30  per  cent.,  because  he  is  never  sure  about  the  end  point. 
Professor  Walker  defended  the  utility  of  the  titration  method  in  a 
reply  to  Mr.  MacEwan  in  the  issue  of  February  10,  1896,  and  stated 
that  further  investigation  had  shown  that  five  minutes'  maceration 
was  ample  for  the  completion  of  the  reaction.  As  stated  at  the  begin- 
