5H 
Theory  of  Indicators,  etc. 
J  Am.  Jour.  Pharm. 
\  November,  1904. 
interfering  with  the  drops.  It  may,  however,  be  said  that  a  marked 
variation  between  the  phenolphthalein  end  point,  after  allowing  for 
phosphates  and  the  gravimetrically  determined  total  available 
hydrochloric  acid,  is  seldom  to  be  recorded  within  three  or  four 
hours  from  the  commencement  of  the  process  where  normal  peptic 
digestion  is  concerned. 
A  long  series  of  determinations  of  total  nitrogen  and  of  nitrogen 
in  the  phosphotungstic  filtrate  in  comparison  with  the  figures 
obtained  on  volumetric  titration  with  phloroglucinvanillin  drops, 
alizarin  and  phenolphthalein  has  failed,  as  would  be  expected  from 
the  above,  to  show  any  close  relationship.  After  correcting  the 
differences  between  the  end  points  of  drops  and  alizarin,  alizarin  and 
phenolphthalein  end  drops  and  phenolphthalein,  for  the  effect  due 
to  phosphates  and  other  secondary  causes,  the  widest  variation  is 
TABLK  IV. 
Case. 
i 
2 
3 
4 
5 
6 
7 
8 
9 
10 
Avg. 
Alizarin  to  Phenolphthal- 
25 
19 
30 
26 
43 
3i 
17 
31 
2t 
35 
4 
2 
5 
4 
5 
4 
1 
5 
3 
5 
21 
25 
22 
38 
27 
.6 
26 
18 
3° 
24  0 
"3 
107 
120 
228 
135 
8d 
127 
104 
144 
128-9 
Phosphotungstic  filtrate  .  . 
23 
'9 
23 
27 
40 
26 
18 
24 
19 
27 
24-6 
still  found  to  obtain  in  the  ratio  of  these  figures  to  the  total  nitro- 
gen and  phosphotungstic  nitrogen.  The  range  from  alizarin  to 
phenolphthalein  is  generally  from  a  fifth  to  a  sixth  of  the  total 
nitrogen,  as  is  the  phosphotungstic  nitrogen.  The  range  from  drops 
to  alizarin  varies  far  more,  and  that  of  drops  to  phenolphthalein  may 
be  anything  from  a  half  to  a  tenth  of  the  total  nitrogen,  but  it  may 
be  said  that  where  the  digestion  is  advanced,  the  titration  range  is 
higher  in  proportion  to  the  total  nitrogen,  and  that  the  highest  rel- 
ative figures  are  obtained  in  those  cases  in  which  secondary  decom- 
position is  well  marked.  The  results  of  this  nature  have  usually 
been  confirmed  by  finding  discrepancies  between  the  volumetric  and 
gravimetric  estimation  of  chlorides.  Both  these  factors  may  be 
taken  to  indicate  the  probable  liberation  of  amido  and  carboxylic 
groups  having  a  specific  effect  upon  the  state  of  equilibrium  of  indi- 
vidual indicators.    That  the  phloroglucinvanillin  end  point  actually 
