Am'Mayl'is93arm'}    Constituents  of  Commercial  Peptone.  245 
at  once  submitted  to  Kjeldahl's  process,  and  a  correction  is  made 
for  the  nitrogen  in  the  paper.  This  gives  the  amount  of  unchanged 
albuminous  substances.  In  a  well  made  preparation  these  should 
not  be  present.  The  nitrogen  in  the  filtrate  is  also  determined,  and 
the  sum  of  the  two  stated  as  total  nitrogen.  A  fresh  portion  of 
substance  dissolved  in  25  cc.  of  water  (or,  if  a  liquid,  50  cc.  concen- 
trated to  25  cc),  is  gradually  mixed  with  250  cc.  of  absolute  alcohol, 
and  filtered  after  12  hours.  The  filtrate,  which  contains  the  gelatin- 
peptone,  the  leucin,  tyrosin,  and  other  decomposition  products,  is 
freed  from  alcohol  and  dissolved  in  water.  Any  insoluble  matter 
is  filtered  off,  and  regarded  as  albumose.  The  clear  solution  is  made 
up  to  500  cc,  and  100  cc.  of  this,  warmed  to  about  400,  is  precipitated 
with  10-15  cc.  of  a  paste  of  mercuric  oxide,  containing  about  15  per 
cent.,  and  prepared  by  pouring  mercuric  chloride  into  dilute  soda, 
washing  thoroughly,  and  preserving  in  the  dark.  After  stirring  for 
a  few  minutes,  the  mixture  is  filtered  and  the  nitrogen  determined 
in  the  precipitate  and  filtrate.  The  former  contains  the  gelatin- 
peptone,  with  unknown  decomposition  products  of  albumose  and 
peptone.  The  filtrate  contains  the  leucin,  tyrosin,  and  other  pro- 
ducts of  a  digestive  fermentation  which  has  been  carried  to  excess, 
together  with  part  of  the  so-called  flesh  bases  (creatin,  etc.),  which 
are  very  sparingly  soluble  in  95  per  cent,  alcohol.  Instead  of 
mercuric  oxide,  phosphotungstic  acid  may  be  used.  This  reagent, 
used  in  excess,  precipitates  none  of  the  flesh  bases  except  xanthin 
and  hypoxanthin,  of  which,  from  their  sparing  solubility,  only  traces 
can  be  present  in  the  alcoholic  solution. 
The  alcohol  precipitate  containing  the  albumose,  gelatin  and 
peptone  is  rinsed  with  water  into  a  beaker  and  warmed  until  the 
alcohol  is  expelled.  Any  albumose  which  has  been  rendered 
insoluble  is  filtered  off  and  washed  with  hot  water.  The  clear  solu- 
tion is  made  up  to  500  cc,  and  of  this.  50  cc,  mixed  cold  with  an 
equal  volume  of  dilute  sulphuric  acid  (1  vol.  to  3  vols,  of  water), 
is  completely  precipitated  with  phosphotungstic  acid.  The  nitrogen 
in  the  precipitate  gives  the  joint  amount  of  the  albumose,  peptone 
and  gelatin.  100  cc.  of  the  same  solution,  concentrated  on  the 
water-bath  to  8- 10  cc,  is  mixed  with  100  cc.  of  a  cold  saturated 
solution  of  ammonium  sulphate.  The  precipitate  is  collected  and 
washed  with  a  saturated  solution  of  ammonium  sulphate.  It  is  then 
dissolved  in  tepid  water,  and  whilst  one  portion  of  the  solution  is 
