1 14  Ammonium  in  Diluted  Phosphoric  Acid.  {^JgaJIP*' 
the  temperature  was  maintained  at  from  ioo°  to  1300,  and  the  mixture 
was  finally  boiled  to  dissolve  the  last  portions  of  phosphorus. 
A  third  sample  was  obtained  from  Dr.  Pile,  who  employed  no  heat 
in  the  process,  but  on  the  contrary,  kept  the  mixture  in  cool  water 
until  complete  solution  of  the  phosphorus  was  effected.  A  fourth 
sample  was  procured  from  a  fellow-student,  C.  S.  Hallberg,  who 
placed  the  mixture  in  cool  water  for  24  hours,  during  which  time  about 
two-thirds  of  the  phosphorus  was  dissolved,  and  then  resorted  to  boil- 
ing for  completing  the  solution. 
Owing  to  the  impossibility  of  estimating  phosphoric  acid  by  direct 
saturation,  on  account  of  the  very  gradual  change  from  an  acid  to  an 
alkaline  condition,  a  seemingly  intricate,  but  practically  very  simple 
process  was  adopted.  Half  a  fluidounce  of  the  diluted  acid  was  super- 
saturated with  caustic  soda,  and  the  mixture  placed  in  a  small  flask,  to 
which  was  adapted,  by  means  of  a  tightly  fitting  cork,  a  bent  glass  tube, 
the  end  of  which  was  allowed  to  dip  slightly  into  10  cubic  centimetres 
of  a  decinormal  solution  of  oxalic  acid.  The  apparatus  was  so  con- 
structed as  to  prevent  the  possibility  of  any  of  the  alkali  passing  me- 
chanically into  the  distillate,  and,  as  a  further  precaution,  preference 
was  given  to  caustic  soda  for  saturating  the  acid,  so  that  in  case  the 
smallest  quantity  passed  over,  it  might  be  detected  by  the  flame  test, 
which,  however,  in  every  experiment  failed  to  reveal  a  trace.  Heat 
was  then  applied  by  means  of  a  sand  bath,  until  one-half  or  more  of  the 
liquid  had  distilled  over.  To  the  mixture  of  the  distillate  and  oxalic 
acid  solution,  previously  reddened  with  litmus,  was  added  a  decinormal 
solution  of  ammonia,  the  deficiency  required  for  neutralization  gave 
the  cubic  centimetres  of  a  decinormal  solution  of  ammonia  equal  to 
that  contained  in  the  diluted  phosphoric  acid,  and,  from  this,  the  re- 
sults in  the  subjoined  table  were  calculated.  With  one  exception,  two 
experiments  were  made  with  each  sample,  and  when  there  were  any 
differences,  which,  however,  were  very  slight,  an  average  was  taken 
upon  which  the  calculations  were  based.  From  the  proportion  of 
phosphorus  directed  by  the  Pharmacopoeia,  there  are  found  to  be  but 
56*90  grains  of  actual  phosphoric  acid  (H3P04)  in  each  fluidounce. 
Therefore,  the  foundation  was  comparatively  small  to  build  the  estima- 
tion on.  The  following  schedule  gives  the  results,  which,  small  as 
they  may  appear,  were,  nevertheless,  readily  obtained  by  the  method 
above  described. 
