330  Quantitative  Estimation  of  Phosphates.  {AmjJu01^'19Pot.arm- 
(2)  Difference  between  phenolphthalein  end  point  and  phenoltalein 
end  point  in  presence  of  BaCl2  =  0-85  c.c.  n/10  acid,  from 
which  phosphoric  effect  for  50  c.c.  of  stomach  contents  employed 
is  altogether  equivalent  to  4-12  c.c.  of  a  one-tenth  normal  acid,  and 
is  made  up  as  follows  : 
From  alizarin  to  phenolphthalein  end  point,  ==  2-0  c.c. 
From  phenolphthalein  to  phenolphthalein  BaCl2  end  point,  == 
2-12  c.c. 
Consequently  the  effect  on  1 00  c.c.  of  stomach  contents  would  be 
respectively  4  c.c.  and  4-24  c.c,,  total  8-24  c.c,  which  means  that  for 
10  c.c  of  contents,  the  effect  attributable  to  phosphates  would 
be,  in  this  case,  0-41  before  the  alizarin  end  point,  and  0-41  between 
alizarin  and  phenolphthalein  end  points,  giving  a  total  effect  of 
0*82,  on  a  total  acidity  of  4.5  c.c.  This  result  was  confirmed  by 
means  of  uranium  nitrate  standard  solution. 
Summary. — It  has  been  shown  that  the  usual  method  of  roughly 
estimating  the  effect  due  to  acid  phosphates  in  the  titration  of  stom- 
ach contents  is  absolutely  incorrect ;  that  one  of  the  three  acid  affini- 
ties of  phosphoric  acid  is  saturated  at  the  alizarin  end  point,  and  a 
second  at  the  phenolphthalein  end  point.  Consequently  less  than 
one-half  of  the  total  effect  due  to  phosphates  lies  between  the  diazo 
(so-called)  and  alizarin  end  points  ;  whilst  at  least  an  equal  effect 
is  exerted  on  the  portion  usually  looked  upon  as  combined  HC1. 
A  comparatively  simple  method  has  been  suggested  whereby  a 
fairly  accurate  estimate  of  the  phosphates  present  and  the  effect 
which  they  exert  may  be  directly  determined,  dependent 
(1)  Upon  the  transition  from  NaH2P04  to  Na2HP04  between  the 
alizarin  and  phenolphthalein  end  points; 
(2)  The  transition  from  Na2HP04  to  Na3P04  between  the  phe- 
nolphthalein end  point  alone  and  in  the  presence  of  BaCl2,  whereby 
the  alkaline  Na3P04  is  converted  into  Ba3(POJ2  so  soon  as  found  and 
thus  removed  from  the  scene  of  action. 
Incidentally,  one  object  of  this  paper  is  to  draw  attention  to  the 
gross  inaccuracies  in  the  accepted  methods  of  titrating  stomach 
contents. 
