362  The  F lash-Point  in  Mineral  Oils.     {Am  #|£ ^ad- 
mixture of  amido-acids.  This  residue,  in  all  cases,  when  dried  in  a 
vacuum  at  the  ordinary  temperature,  has  the  composition  ;«C9H18 
N205 ;  if  heated  at  ioo°,  it  loses  water.  The  similar  residue  obtained 
from  the  fraction  soluble  in  alcohol  has  the  composition  wC9H20N2O5. 
Phosphotungstic  acid,  free  from  alkalis,  precipitates  only  about 
half  the  fibrin  peptone.  The  precipitated  fraction,  when  separated 
from  the  phosphotungstic  acid  and  dried  in  a  vacuum  over  sulphuric 
acid,  is  a  colorless,  friable  substance,  soluble  in  water  but  not  hygro- 
scopic. It  contains  oxygen  and  nitrogen  in  the  ratio  of  1-27:  i,and 
carbon  and  hydrogen  in  the  ratio  of  about  I  :  1-9.  When  heated 
with  barium  hydroxide,  it  loses  about  one-fourth  of  its  nitrogen  in 
the  form  of  ammonia  and  1  mol.  of  carbonic  anhydride  is  liberated  for 
every  2  mols.of  ammonia.  The  residue  of  amido-acids  has  the  com- 
position /(CnH2nN204)  or  CmH2mN02,  ^  being  between  9  and  10  and 
very  near  9. 
The  portion  not  precipitated  by  phosphotungstic  acid  contains 
oxygen  and  nitrogen  in  the  ratio  of  2  :  1,  and  carbon  and  hydrogen  in 
the  ratio  of  1  :  17.  When  heated  with  barium  hydroxide,  it  loses  one- 
fifth  of  its  nitrogen  in  the  form  of  ammonia.  1  mol.  of  carbonic 
anhydride  is  formed  for  every  2  mols.  of  ammonia,  and  the  other  pro- 
ducts are  acetic  acid  and  a  residue  of  amido-acids  of  the  composi- 
tion /(CnH2nN206)  where  n  is  again  between  9  and  10  and  is  very 
near  9. 
The  portion  of  the  fibrin  peptone  soluble  in  alcohol  gives  similar 
results  except  that  it  contains  CuH2n+2  instead  of  CnH2n. 
It  follows  that  fibrin  peptone  from  the  horse  can  be  split  up  into 
two  parts  by  the  action  of  phosphotungstic  acid,  one  which  is  pre- 
cipitated and  contains  a  lower  proportion  of  oxygen,  and  another 
which  is  not  precipitated  and  contains  a  higher  proportion  of  oxygen. 
The  excess  of  oxygen  in  the  latter  exists  in  the  form  of  hydroxyl,  and 
the  fibrin  itself  must  be  regarded  as  a  compound  either  hydrolysable 
by  pepsin,  yielding  two  products  which  are  both  ureides. 
THE  FLASH-POINT  AND  POINT  OF  DANGER  IN 
MINERAL  OILS.1 
By  D.  R.  Steuart,  F.I.C.,  F.C.S. 
The  danger  of  fire  or  explosion  from  a  mineral  oil  is  tested  by 
taking  its  flash-point.    The  Government  test  of  Professor  Abel  is  a 
1  Chemical  News,  June  23,  1893,  p.  291. 
