Aja^uaryfi898m'}      Analysts  of  the  Gastric  Contents.  37 
acids  total  from  the  total  acidity.  This  method  is  very  simple.  It 
is  not,  however,  absolutely  accurate,  since  the  total  acidity  due  to 
acid  salts  is  contained  in  the  total  recorded  as  total  hydrochloric 
acid.38 
A  review  of  all  these  precipitation  and  ash  methods  produced  up 
to  1 891  maybe  found  in  Martius  and  Luttke's  "  Magensaure  d. 
Menschen." 
The  method  of  the  estimation  of  the  total  hydrochloric  acid  by 
color  analysis  includes  the  following  determinations  :39 
{a)  The  determination  of  the  total  acidity  by  phenolthalein. 
(&)  The  determination  of  the  total  acidity  due  to  free  acids  and 
acid  salts  by  alizarin  or  Congo  red. 
(V)  The  determination  of  the  total  combined  acids  by  subtraction 
of  b  from  a. 
(d)  The  determination  of  the  total  free  hydrochloric  acid  by 
phloroglucin-vanillin  or  di-methyl-amido-azo-benzoL 
(e)  The  determination  of  the  total  hydrochloric  acid  by  the  addi- 
tion of  c  and  d. 
This  color-analysis  method  has  not  the  absolute  accuracy  of  the 
precipitation  methods. 
It  is,  however,  of  sufficient  accuracy  for  comparative  work,  and 
has  the  advantage  of  a  simplicity  fitting  it  for  ordinary  clinical 
work. 
The  details  of  this  color-analysis  process  are  as  follows  :  The 
estimations  are  all  made  by  titration  of  the  contents  with  a  deci- 
normal  solution  of  sodic  hydrate.40  Each  cubic  centimetre  of  this 
soda  solution  is  capable  of  neutralizing  0-00365  gramme  of  hydro- 
chloric acid.  The  estimation  of  the  total  acidity  (a)  is  made  by 
titration  against  the  indicator  phenolthalein.  This  reagent  gives  a 
red  color  in  an  alkaline  solution,  no  color  in  acid  solution.  Ten  cubic 
centimetres  of  the  mixed  contents  are  diluted  with  water,  and  two 
or  three  drops  of  a  1  per  cent,  alcoholic  solution  of  phenolthalein 
added.  To  this  mixture  the  decinormal  soda  solution  is  added  from 
a  graduated  burette  until  a  definite  red  color  appears  and  remains 
38  Hari :  Archivf.  Verdauungskrankheiten,  Bd.  II,  H.  203. 
3  9  This  plan  of  analysis  is  that  originated  by  Topfer,  with  some  modification 
of  the  tests.    Topfer  :  Zeitschr.f.  Physiol.  Chemie,  Bd.  XIX,  H.  1. 
40  One-tenth  molecular  weight  of  NaOH  +  1,000]  c.c.  distilled  water  =  4 
grammes  to  1,000  c.c. 
