158 
Analysis  of  Peptones. 
( Am.  Jour.  Pharm. 
\      March,  1892. 
holds  that  in  a  well-prepared  peptone  the  alcohol  extractive  should 
not  exceed  30  per  cent.,  but  we  are  inclined  to  think  this  too  low  an 
estimate.  A  large  proportion  indicates  that  leucine,  tyrosine,  and 
other  products  of  metamorphosis  are  present.  It  is  evident  that 
this  process  is  not  intended  to  replace  more  exact  methods  of 
analysis.  Its  greatest  defect  is  that,  if  gelatin  had  been  added  to 
the  peptone,  it  would  be  precipitated  by  alcohol,  and  would,  there- 
fore, be  weighed  with  the  nutritive  constituents. 
THE  MODIFIED  PROCESS. 
It  is  convenient  to  work  with  a  tolerably  concentrated  solution. 
Any  portion  insoluble  in  warm,  but  not  boiling  water,  may  be 
removed  by  filtration,  and  treated  separately  for  nitrogen,  etc.  If 
a  jelly  be  under  examination  it  must  be  liquefied  by  heat  or  by 
dilution.  In  the  following  synopsis  a  strength  of  about  20  per  cent, 
of  solid  matter  is  assumed.  It  is  obvious  that  in  any  such  scheme 
of  analysis  the  mineral  salts  must  be  included  among  the  organic 
proximate  constituents,  for  our  knowledge  does  not  yet  permit  us 
to  assign  to  albumose,  peptone,  and  the  like,  any  definite  proportion 
of  mineral  compounds.  It  is  best  to  make  separate  estimations  of 
water,  ash  and  total  nitrogen. 
(1)  Water;  ash;  total  nitrogen. — Estimated  as  usual.  About  3 
grams  for  water  and  ash  and  about  I  gram  for  total  nitrogen,  by 
the  Kjeldahl  method,  are  convenient  quantities. 
(2)  Albumin;  gelatin  insoluble  in  alcohol  {coagulable  gelatin); 
albumose;  peptone. — 40  grams  of  fluid  peptone  containing  about 
80  per  cent,  of  water  are  dropped  gradually  into  300  cc.  of  nearly 
anhydrous  alcohol,  in  a  large  weighed  beaker  and  the  mixture 
agitated  by  gentle  centrifugal  motion.  After  an  hour  or  so  the 
above-named  compounds  will  have  separated  and  can  be  washed 
with  absolute  alcohol  by  decantation.  The  alcoholic  solution  is 
preserved  for  further  treatment  and  is  hereafter  alluded  to  as  the 
stock  alcoholic  solution.  The  beaker,  with  its  contents,  is  then  dried 
to  constant  weight  at  100°  C. 
(a)  Albumin. — The  weighed  alcoholic  precipitate  is  digested  with 
warm  water  and  washed  on  a  tared  filter.  The  residue,  which  has 
been  rendered  insoluble  by  the  alcohol,  is  weighed  as  albumin. 
The  filtrate  from  albumin  is  diluted  with  water  to  250  cc.  This 
may  be  described  as  the  stock  aqueous  solution. 
