368 
Gasometric  Analysis. 
f  A.m.  Jour.  Pharm. 
\     August,  1900. 
slowly  run  into  the  funnel  and  from  this  into  the  bottle  by  com- 
pressing the  rubber  tubing  (prevent  air  from  entering  the  bottle  by 
not  allowing  the  liquid  to  get  lower  than  the  zero  mark),  rinse 
funnel  and  tubing  with  5  c.c.  alcohol,  then  introduce  10  c.c.  potas- 
sium iodide  (10  per  cent.),  and  lastly  10  c.c.  diluted  sulphuric  acid 
(10  per  cent.),  added  in  portions  to  prevent  too  violent  liberation  of 
gas  and  consequent  pressure  which  might  result  in  some  gas  escap- 
ing through  the  funnel.  (The  alcohol  is  used  as  stated  to  rinse  in 
the  "  nitre  "  and  thus  prevent  liberation  of  gas  which  always  takes 
place  when  ethyl  nitrite  comes  in  contact  with  water  or  aqueous 
solutions  ;  if  such  a  decomposition  takes  place  above  the  glass  plug 
the  gas  escapes  into  the  air  and  is  lost  in  the  assay.)  Mix  the  re- 
agents first  by  gentle  agitation,  and  after  evolution  of  gas  ceases  by 
more  vigorous  agitation ;  allow  to  stand  ten  to  fifteen  minutes,  lift 
the  syphon-tube  from  the  graduated  cylinder  and  read  the  volume 
of  displaced  fluid  ;  subtract  from  this  the  volume  of  the  added 
reagents  to  obtain  the  volume  of  nitrogen  dioxide  from  the  sweet 
spirit  of  nitre  ;  divide  the  volume  of  gas  by  that  of  the  nitre  used 
to  obtain  the  volumes  of  gas  from  one  volume  of  spirit  of  nitrous 
ether  (eleven  volumes  at  or  near  25 0  C,  U.S. P.). 
Of  the  various  factors  which  influence  the  volumes  of  gases,  as 
temperature,  barometric  pressure,  solubility  and  tension  of  the 
aqueous  vapor,  the  last  three  are  disregarded,  but  for  temperature 
the  U.S.P.  gives  the  value,  in  terms  of  amyl,  ethyl  and  sodium 
nitrites,  of  1  c.c.  gas  at  0°  and  25 0  C,  besides  a  table,  by  which 
corrections  can  be  made  from  o°  to  400  C. 
ESTIMATION  OF  SODIUM  NITRITE. 
To  estimate  sodium  nitrite  dissolve  0-150  gm.  in  5  c.c.  water,  intro- 
duce into  the  apparatus,  rinse  with  10  c.c.  water  and  follow  with  10 
c.c.  potassium  iodide  and  10  c.c.  diluted  sulphuric  acid  and  proceed  as 
previously  described;  the  volume  of  gas  from  0-150  gramme  should 
measure  not  less  than  50  c.c.  at  150  C,  or  517  c.c.  at  25 0  C.  (97*6 
per  cent,  pure  NaNo2  U.S.P.).  Repeated  comparisons  of  the  de- 
scribed apparatus  with  nitrometers  have  been  made  during  the 
past  six  months  in  the  estimation  of  spirit  of  nitrous  ether  and  of 
sodium. nitrite,  and  the  uniformly  agreeing  results  obtained  by  differ- 
ent persons  warrant  the  recommendation  as  an  inexpensive  substi- 
tute for  a  nitrometer;  the  only  advantage  possessed  by  the  latter 
depends  upon  its  graduation. 
