Am.  Jour.  Pharm.  \ 
October,  1904.  J 
Theory  of  Indicators,  etc. 
465 
Several  series  of  experiments  were  carried  out,  making  use  of  the 
solutions  of  Witte's  peptone,  varying  in  strength  from  complete 
saturation  to  I  per  cent.  This  substance  was  employed  for  testing 
indicators  in  preference  to  stomach  contents  and  artificial  peptic 
mixtures,  owing  to  its  relative  purity  and  freedom  from  inorganic 
impurities  capable  of  producing  a  disturbing  effect  upon  the  end 
points,  and  also  on  account  of  the  ease  with  which  the  small  quan- 
tities of  such  substances  present  can  be  determined.  The  experi- 
ment was  repeated  on  five  separate  occasions,  peptone  solutions  of 
different  concentrations  and  obtained  from  different  batches  being 
employed.  In  order  that  there  should  be  no  possible  source  of  error 
due  to  decomposition  of  the  peptone  solution,  each  series  of  experi- 
ments was  carried  out  in  the  space  of  twenty-four  hours,  as  follows : 
In  the  first  case  a  saturated  solution  was  obtained  by  shaking 
repeatedly  100  grammes  of  peptone  with  10  liters  of  water,  filtering 
and  completely  admixing  the  filtrate.  From  this  clear  solution 
IOO  c.c.  portions  were  removed  for  titration  alone  and  in  the  presence 
of  various  acids  by  using  each  of  the  indicators  under  investigation. 
At  the  same  time  200  c.c.  batches  were  removed  for  the  estimation 
of  those  substances  capable  of  acting  on  indicators,  phosphates, 
chlorine  salts,  total  chlorides  and  ammonium  chloride  and  organic 
acids,  all  experiments  being  made  in  duplicate.  The  nitrogen  con. 
tent  of  the  solution  was  also  estimated  by  removing  25  c.c.  portions 
for  direct  Kjeldahl  determinations  and  50  c.c.  portions  were  treated 
with  an  equal  amount  of  20  per  cent,  phosphotungstic  acid  at  700, 
filtered  and  nitrogen  estimated  in  the  filtrate.  In  this  case  100  c.c. 
of  the  solution  was  found  to  contain  nitrogen  equivalent  to  92  c.c. 
n/10  alkali.  The  amount  of  substance  capable  of  materially  affect- 
ing the  end  points  of  indicators  was  practically  negligible,  hydro, 
chloric  acid  being  less  than  -3  c.c,  phosphoric  acid  -2  ex.,  and 
organic  acids  less  than  -I  c.c.  of  n/  10  alkali. 
Volumetric  determinations,  carried  out  with  both  warm  and  cold 
solutions,  between  which  little  difference  in  results  was  observed, 
show  as  an  average  : 
Porrier's  blue  indefinite,  roo  c.c.  peptone  =  over  4-o  c.c.  alkali. 
Phenolphthalein,  100  c.c.  peptone  ==  4*0  c.c.  alkali. 
Alizarin,  100  c.c.  =  4*0  acid. 
Litmus,  100  c.c.  =  2*5  to  3  c.c.  acid,  from  purple  to  red.    End  point  indefinite. 
Phlorogluciuvauillin  drops,  100  c.c.  solution  requires  from  20  to  20  5  c.c.  n/10 
acid. 
