878 
Nucleic  Acid. 
Am.  Jour.  Pharm. 
Dec,  1918. 
cupric  acetate,  calcium  chloride  and  silver  nitrate  the  reactions  de- 
scribed above. 
Tests  for  the  Absence  of  Protein. 
Biuret  Reaction. — A  solution  of  the  acid  in  an  excess  of  caustic 
soda  should  give,  on  the  addition  of  one  or  two  drops  of  dilute 
copper  sulphate  solution,  a  greenish-blue  color  with  at  the  most  a 
faint  tinge  of  purple.  This  test  is  quite  sufficient,  but  occasionally 
the  following  test  is  applied: 
A  5  per  cent,  solution  of  nucleic  acid  in  a  small  excess  of  am- 
monia, when  heated  in  a  bath  at  105 0  C,  should  give  at  the  most  a 
slight  turbidity. 
In  connection  with  these  tests,  it  may  be  pointed  out  that  the  re- 
moval of  the  last  traces  of  protein  matter  from  nucleic  acid  involves 
a  very  troublesome  series  of  treatments,  and  that  acid  of  high  com- 
mercial quality  will  usually  give  an  indication  of  the  presence  of 
traces  of  protein  when  subjected  to  the  above  tests.  The  second  of 
the  above  tests  is  the  more  severe,  inasmuch  as  an  amount  of  protein 
equal  to  not  more  than  0.1  or  0.2  per  cent,  (expressed  on  the  acid) 
gives  a  very  appreciable  volume  of  precipitate. 
Inorganic  Phosphate. — To  a  solution  of  the  acid  in  excess  of 
ammonium  or  sodium  acetate  a  few  drops  of  acetic  acid  are  added, 
and  then  a  little  uranium  acetate,  A  flocculent  precipitate  is  formed, 
which  in  the  absence  of  more  than  a  trace  of  inorganic  phosphate 
should  dissolve  completely  on  boiling.  A  considerable  excess  of 
alkaline  acetate  is  necessary  in  this  test. 
'Estimation  of  Nitrogen  and  Organic  Phosphorus. 
Nitrogen. — This  is  estimated  by  the  Kjeldahl  method  in  the  or- 
dinary way. 
Phosphorus. — A  weighed  quantity  of  the  acid  is  -fused  with  six 
times  its  weight  of  sodium  carbonate  containing  10  per  cent,  of 
potassium  nitrate.  The  fused  mass  is  taken  up  with  water,  and  in 
this  solution  the  phosphoric  acid  is  estimated  either  by  the  molybdate 
method  or  by  direct  precipitation  with  magnesia  mixture  in  the 
presence  of  a  little  ammonium  citrate. 
It  will  be  seen  that  the  formula  given  above  corresponds  with 
16. 1  per  cent,  of  nitrogen  and  9.5  per  cent,  of  phosphorus. 
Commercial  nucleic  acid  of  good  quality  ought  to  contain  not 
