466 
Theory  of  Indicators,  etc. 
( Am.  Jour.  Pharm. 
I     October,  1904. 
Tropaeolin  drops,  100  c.c.  solution  requires  from  22  to  22  5  c.c.  n/10  acid. 
Diazo,  yellow-green  reaction  at  the  start  gives  orange-pink  end  point  first  about 
15  c.c.    End  point  indefinite. 
Hematoxylin,  congo-red,  methyl-orange  and  rosolic  acid  give  indefinite  end 
points. 
It  will  be  seen  from  these  figures  that  for  ioo  c.c.  of  solution  there 
is  a  difference  between  phenolphthalein  and  alizarin  end  points  of 
approximately  8  c.c.  n / 10  acid  or  alkali.  Of  this  amount  less  than 
one-tenth  part  can  be  acounted  for  as  combined  HCl,  acid  phos- 
phates, organic  acids  and  other  impurities.  The  effect  observed 
must  consequently  be  attributed  to  the  peptone  itself,  probably  to 
the  weak  basic  groups  contained  in  its  molecule.  Of  the  portion 
equal  to  4  c.c.  from  the  commencement  to  the  phenolphthalein  end 
TABLE  II. 
Titration  of  Peptone  Solutions. 
llin 
t. 
-d 
a 
W 
If? 
&w 
0 
Impurities— Maximo  m 
Effect. 
No. 
Phloroglucinvani 
Drops,  End  PoinI 
Alizarin  End  Poi 
Phenolphthalein 
Point. 
Total  Range  Drc 
Phenolphthalein 
Point. 
Drops  —  Alizarin 
Alizarin  =  Phei 
phthalein. 
Total  Nitrogen. 
HCl,  Free  and 
Combined  with 
Proteids. 
Phosphates. 
Organic  Acids. 
1 
—  7'5 
—  i;6 
+  r6 
5-9 
3*2 
36*2 
•1 
Nil 
2 
—  20  0 
—  4-0 
+  40 
24* 
16 
8 
92 
•3 
•2 
"1 
3 
—  34  0 
—  57 
+  5"i 
39"  1 
28-3 
io-8 
131 
'5 
•4 
4 
—  64  0 
—  i3-4 
+  8-2 
72-2 
50-6 
216 
242 
•8 
5 
—  70*0 
—  17  0 
+  12 
82-0 
53'o 
29*0 
281 
•9 
•8 
point,  less  than  one-tenth  can  be  accounted  for  as  due  to  combined 
chlorides. 
The  period  from  phloroglucinvanillin  end  point  to  that  of  phe- 
nolphthalein is  twenty-four,  about  three  times  that  from  alizarin  to 
phenolphthalein  and  less  than  one-quarter  of  the  equivalent  of  the 
total  nitrogen  present  in  the  solution. 
In  the  following  table  we  have  recorded  results  obtained  with 
solutions  of  Witte's  peptone  varying  from  -03  to  -4  per  cent,  nitro- 
gen. To  make  clear  the  relationship  between  the  nitrogen  content 
and  the  titration  from  the  phloroglucinvanillin  drops'  end  point  to 
alizarin  and  alizarin  to  phenolphthalein,  we  have  recorded  in  one 
