AmjJuiv?i£)3arm'}     Quantitative  Estimation  of  Phosphates.  327 
If  we  now  turn  to  a  consideration  of  the  methods  usually  em- 
ployed in  analyzing  stomach  contents,  and  remember  that  the  dif- 
ference between  the  dimethyl-amido-azo-benzol  end  point  and  the 
alizarin  end  point  is  usually  considered  as  due  to  acid  phosphates 
and  organic  acids,  whilst  the  residual  portion  of  the  titration  from 
alizarin  to  phenolphthalein  is  not  usually  considered  to  be  in  any 
sense  due  to  phosphates,  but  entirely  to  combined  hydrochloric  ;  it 
is  obvious  that  some  discrepancy  exists.  The  results  of  our  analy- 
ses with  normal  phosphates  and  phosphoric  acid,  checked  by  gravi- 
metric methods,  have  proved  conclusively  that  two  of  the  three 
available  acid  groups  of  the  phosphoric  acid  are  neutralized  in  the 
course  of  the  titration  of  stomach  contents  up  to  the  phenolphtha- 
lein end  point ;  that  one  only  of  these  is  neutralized  at  the  alizarin 
end  point;  that  is  to  say,  that  one  of  the  three  acid  equiva- 
lents of  the  phosphates  present  in  stomach  contents  is  continually 
mistaken  for  combined  acid,  whilst  the  difference  between  the 
dimethyl-amido-azo-benzol  and  alizarin  end  point  is  seldom  sufficient 
to  account  for  even  one  of  these  groups,  since  dimethyl-amido-azo- 
benzol  always  reacts  to  a  certain  extent  to  phosphoric  acid  and  the 
alizarin  end  point  is  sharp  on  saturation  of  one  acid  affinity. 
Realizing  this  discrepancy  and  finding  that  it  interfered  seriously 
with  a  long  series  of  comparative  experiments  which  have  been 
carried  out  in  the  laboratory  regarding  chlorides,  nitrogen,  etc.,  of 
stomach  contents,  we  at  first  attempted  to  estimate  the  phosphates 
gravimetrically  and  volumetrically  by  means  of  uranium  nitrate, 
subsequently  allowing  for  the  effect  produced  by  the  known  quan- 
tity of  phosphoric  acid,  but  the  amount  of  available  material  is  usu- 
ally so  small  as  to  render  either  of  these  methods  extremely  un- 
satisfactory, and  we  w7ere  eventually  led  to  adopt  the  following 
method,  which  is  comparatively  simple  and  fairly  accurate,  affording, 
as  it  does,  a  means  of  checking  one's  results  by  duplicate  experi- 
ments : 
As  large  a  quantity  of  the  contents  as  possible,  in  no  case  less 
than  20  c.c,  is  evaporated  to  dryness  in  a  platinum  dish  and  gently 
incinerated  in  order  to  destroy  organic  acids.  The  residue  is  ex- 
tracted with  a  small  amount  of  dilute  sulphuric  acid  free  from 
phosphates;  made  up  to  25  c.c,  two  batches  of  10  c.c.  each  being 
employed  for  the  analyses,  which  are  carried  out  in  the  following 
manner  :  (1)  Under  ordinary  circumstances,  a  one-tenth  normal  solu- 
