Am.  Jour.  Pharm. 
July,  1889. 
Estimation  of  Proteids. 
363 
salt,  C^oH.^OgEtj  was  obtained  as  a  heavy  oil  by  acting  on  the  silver 
salt  with  ethyl  iodide.  On  distillation,  it  decomposes  with  elimination 
of  water  and  the  formation  of  another  ethyl  salt,  according  to  the 
equation  C2oH2903Et  =  C2oH2702Et+H20.  This  new  compound  is  a 
heavy  yellow  oil  which  yields  a  resin  with  potassium  hydroxide. 
Finally  the  author  shows  that  the  resinification  of  the  acid  when  ex- 
posed to  the  air  consists  in  an  oxidation  accompanied  by  loss  of  water. 
The  acid  described  above  agrees  in  properties  with  Maly's  abietic  acid, 
but  differs  from  it  in  composition. 
ESTIMATION  OF  PROTEIDS  WITH  SPECIAL  REFER- 
ENCE TO  MILK. 1 
By  J.  Sebelien.* 
Milk  contains  three  proteids,  casein,  lactalbumin  and  traces  of  lac- 
toglobulin.  In  order  to  test  the  method  adopted  for  the  quantitative 
estimation  of  the  total  proteids  and  of  the  individual  proteids,  a  num- 
ber of  preliminary  experiments  were  made  with  solutions  of  (1)  pure 
casein  containing  small  quantities  of  calcium  chloride  and  sodium 
phosphate,  (2)  lactalbumin,  and  (3)  egg  albumin.  Ritthausen's  copper 
sulphate  method  of  precipitating  total  proteids  was  first  investigated 
in  the  following  way :  the  total  nitrogen  in  the  proteid  solution,  in  the 
precipitate,  and  in  the  liquid  from  which  the  precipitate  had  been  fil- 
tered off,  was  estimated  by  Kjeldahl's  process.  The  two  first  named 
had  practically  the  same  amount  of  nitrogen  in  them,  whilst  the  fil- 
trate was  free  from  nitrogen.  Lead  acetate  was  similarly  tested  ;  some 
proteid  was  left  in  solution,  and  the  nitrogen  in  the  precipitate  plus 
that  in  the  filtrate  gave  too  high  a  result.  Tannic  acid  was  found  to 
precipitate  all  proteids  completely  ;  the  precipitate  must  however,  not 
be  washed  with  hot  water  or  with  spirit,  as  it  is  partially  soluble  in 
both  those  reagents.  Albumoses  are  only  incompletely  precipitated 
by  tannic  acid,  and  peptone  is  soluble  in  excess  of  the  reagent.  The 
properties  of  phosphomolybdic  acid  are  much  the  same,  except  that 
it  causes  a  more  complete  precipitation  of  both  albumoses  and  pep- 
tone. 
The  question  whether  albumoses  and  peptone  occur  in  milk  was 
then  investigated.    Saturation  with  ammonium  sulphate  completely 
1  Zeit  physiol,  Chem.,  xiii.,  135-180  ;  reprinted  from  Jour.  Chem.  Soc,  April, 
p.  450. 
