464 
Estimation  of  Peptones. 
J  Am  Jour.  Piiarrm. 
I      Sept.,  1881. 
the  other  it  gives  too  low  an  indication,  because  peptone  is  dissolved 
by  99°  alcoliol. 
Take,  for  examplcj  a  solution  of  peptone  free  from  foreign  matters 
and  containing  25  per  cent,  of  pure  peptone.  If  this  be  precipitated, 
by  ten  times  its  weight  of  absolute  alcohol  the  weight  of  dried  pep- 
tone obtained  is  16*91  per  cent.,  the  error  amounting  to  32  per  cent. 
If  simply  the  method  of  operating  be  changed,  and  the  peptone  be 
poured  drop  by  drop  into  the  alcohol,  as  recommended  by  Henninger^ 
the  weight  of  the  peptone  dried  is  18*83  per  cent.,  the  error  being 
diminished  to  24*66  per  cent. 
If  after  hnving  precipitated  tlie  peptone  with  alcohol,  one-half  its 
its  weight  of  ether  be  added,  the  weight  of  dried  peptone  obtained  is 
20*83  per  cent. ;  the  error  is  lower,  but  still  equals  16*68  per  cent. 
In  order,  therefore,  that  this  process  may  be  utilized  it  is  necessary 
to  add  to  the  alcohol  the  half  of  its  weight  of  ether,  so  as  to  deter- 
mine a  more  complete  precipitation.  To  tlie  weight  of  the  peptone 
thus  found,  relatively  to  100  grams  of  solution,  5  grams  should  be 
added,  as  representing  the  quantity  dissolved  in  the  ether  alcohol,  and 
this  will  give  the  total  weight. 
The  estimation  of  the  ash  is  not  worth  notice,  for  it  is  usually  falsi- 
fied by  the  enormous  proportion  of  chloride  of  sodium  present. 
Finally  the  estimation  of  the  nitrogen  may  be  affected  by  the  abnor- 
mal presence  of  gelatin. 
After  this  criticism  upon  the  value  of  the  different  processes  in  use 
it  may  be  shown  that  the  precipitation  by  alcohol  and  the  determina- 
tion of  the  nitrogen  become  satisfactory  processes  for  the  estimation  of 
a  solution  of  peptone  if  it  be  submitted  to  a  preliminary  analysis^ 
The  following  is  the  plan  proposed : 
The  peptone  is  saturated  hot  with  sulphate  of  magnesia;  if  it 
contains  gelatin  this  rises  in  an  elastic  viscous  mass  and  can  be  col- 
lected ;  in  this  case  neither  the  density  nor  alcohol  can  be  employed 
and  it  is  necessary  to  have  recourse  to  the  determinati-on  of  the  nitro- 
gen. The  weight  of  the  nitrogen  due  to  the  gelatin,  subtracted  from 
the  weight  of  the  total  nitrogen,  gives  a  number  which,  multiplied  by 
the  constant  6*05,^  expresses  the  weight  of  dry  and  pure  peptone. 
The  peptone  which  does  not  contain  gelatin  is  diluted  with  twice  its 
^  Fibrine  peptone  contains  16*66  per  cent,  of  nitrogen  (Henninger) ;  albu- 
men peptone  contains  16*38  per  cent.  The  mean  being  16-52,  1  gram  of 
nitrogen  represents  6*05  of  peptone. 
