512 
Theory  of  Indicators,  etc. 
("Am.  Jour.  Pharra. 
\  November,  1904. 
be  said  that  any  given  period  is  a  direct  function  of  any  given  type 
of  combining  nitrogenous  group,  for  the  end  points  of  certain  indi- 
cators are  more  delicate  than  those  of  others.  If  stomach  contents 
were  purely  a  mixture  of  hydrochloric  acid  with  nitrogenous  bodies 
possessed  of  basic  affinities  varying  in  strength  from  that  of  ammo- 
nia to  that  of  the  NH2  group  in  urea,  then  the  final  end  point  should 
be  a  gauge  of  the  total  hydrochloric  acid  and  the  difference  between 
the  final  and  intermediate  end  points  should  be  dependent  upon  the 
quantity  and  degree  of  hydrolysis  of  the  nitrogenous  products  in 
question.  But  this  is  not  the  case.  Phosphates,  organic  acids  and 
other  substances  present  in  small  quantities  interfere  to  an  appre- 
ciable extent  with  results  and  must  be  allowed  for. 
In  the  course  of  the  last  two  years  some  250  stomach  contents 
have  been  examined  after  a  variety  of  test  meals,  that  of  Ewald  being 
employed  by  preference.  In  certain  cases  estimations  were  carried 
out  on  unfiltered  materials,  but  generally  they  were  first  filtered  and 
then  titrated  with  a  series  of  indicators.  Total  chlorine  was  esti- 
mated by  adding  an  excess  of  alkali,  ashing  and  determining  volu- 
metrically  with  silver  nitrate  and  potassium  sulpho-cyanate ;  chlo- 
rine present  as  salts  estimated  by  ashing  directly,  igniting  and 
determining  volumetrically,  the  difference  representing  hydrochloric 
acid  free  and  combined  and  any  ammonium  chloride  that  may  have 
been  present  in  the  original  stomach  contents.  The  phosphates 
were  estimated  volumetrically  by  the  method  described  in  a  pre- 
vious publication,  the  neutralized  stomach  contents  being  evapo- 
rated, ashed,  ignited,  ammonia  removed  by  boiling  with  alkali  and 
carbonic  acid  by  boiling  with  acid,  the  difference  between  the 
alizarin  and  phenolphthalein  end  points  affording  an  accurate  esti- 
mate of  the  effect  attributable  to  phosphates.  Total  nitrogen  was 
determined  by  the  Kjeldahl  process,  as  was  that  present  in  the 
phosphotungstic  filtrate  obtained  on  precipitating  10  c.c.  of  stomach 
contents  with  10  c.c.  of  20  per  cent,  solution  of  phosphotungstic 
acid  containing  2  per  cent,  of  sulphuric  acid.  Lactic  and  other 
organic  acids  when  present  in  sufficient  quantities  to  produce  an 
appreciable  effect  were  estimated  separately. 
In  the  large  majority  of  normal  cases  the  phenolphthalein  end 
point,  after  allowing  for  the  influence  of  phosphates,  was  found  to 
afford  a  fairly  accurate  estimate  of  the  total  available  hydrochloric 
acid  in  the  stomach  contents  ;  that  is  to  say,  hydrochloric  acid,  either 
