370 
Gasometric  Analysis. 
/  Am.  Jour.  Pharm 
(      August.  1900. 
agitate  ;  repeatedly  fill  and  empty  the  homeo  by  proper  inclination 
of  G ;  after  the  evolution  of  gas  ceases  upon  agitation,  allow  to 
stand  ten  to  fifteen  minutes,  lift  the  bottles  and  read  the  volume  of 
displaced  water;  the  number  of  cubic  centimetres  multiplied  by 
0-0027  will  give  the  urea  in  4  c  c.  of  urine. 
No  correction  is  applied  for  the  volume  of  gas  being  under  other 
than  normal  conditions  for  the  reason  that  in  the  decomposition  of 
urea  there  is  involved  a  loss  of  about  8  per  cent,  nitrogen  and  this 
loss  is  just  about  balanced  by  the  effect  of  temperature,  pressure 
and  tension  of  aqueous  vapor  under  ordinary  conditions. 
ESTIMATION  OF  HYDROGEN  DIOXIDE. 
The  gasometric  estimation  of  hydrogen  dioxide  is  possible  in  two 
ways  ;  the  one  generally  followed  starts  with  a  solution  of  potassium 
permanganate  of  such  strength  that  a  definite  volume  is  indicative 
of  a  definite  volume  of  oxygen  without  collecting  and  measuring  the 
latter.  By  using  the  apparatus  described  under  urea,  but  substi- 
tuting acidified  permanganate  instead  of  Labarraque's  solution  and 
hydrogen  dioxide  instead  of  urine,  very  concordant  volumes  of  water 
were  displaced,  one-half  of  which  came  from  the  H202,  the  other 
from  the  K2Mn208.  The  only  objection  was  the  separation  of  man- 
ganic oxide  as  a  brown  stain  upon  the  interior  of  the  apparatus  and 
which  must  be  removed  each  time  by  the  use  of  oxalic  or  sulphu- 
rous acid.  Experiments  were  next  made  with  an  acidified  bichro- 
mate solution ;  this,  of  course,  was  free  from  precipitate,  but  the 
results  varied  according  to  the  rapidity  with  which  the  reagents 
were  allowed  to  mix,  the  volume  of  gas  often  agreeing  with  that 
obtained  with  permanganate,  but  sometimes  was  considerably  below 
this  volume.  The  use  of  an  aqueous  bichromate  solution,  however, 
gave  very  uniform  results,  no  matter  if  0  5  per  cent.,  5  per  cent.,  10 
per  cent,  or  a  saturated  solution  was  used  ;  the  only  difference  no- 
ticeable was  in  the  rapidity  of  the  reaction,  this  increasing  with  the 
stronger  solutions.  Upon  mixing  the  dioxide  with  the  bichromate 
there  is  formed  a  deep  blue  coloration,  changing  through  a  violet  to 
a  brown,  and  finally  into  the  original  orange  color ;  the  bichromate 
is,  therefore,  only  temporarily  oxidized  to  perchromic  acid  or  a  per- 
chromate,  and  this  in  turn  is  reduced  again  to  the  condition  of  bi- 
chromate. The  volume  of  gas  therefore  comes  only  from  the  dioxide. 
The  operation  is  effected  as  follows  :  Place  20  c.c.  saturated  bichro- 
