MEDICAL  ANALYSIS. 
265 
a  solution,  the  original  source  of  which  was  evident  from  the 
odor — cow's  urine.  It  came  from  Germany,  and  was,  no  doubt, 
got  by  the  conversion  of  hippuric  acid  into  benzoic. 
C18H9  N06  +  2HO  =  C4  HB  N04  +  C14H6  04. 
[C9  H9  NO3  +  H2  0  =  C2  W  NO2  +  C7  HG  O2 .] 
Hippuric  Acid.    Water.     GlycOcine.    Benzoic  Acid. 
The  decomposition  may  be  effected  by  sulphuric  acid,  hydro- 
chloric acid,  nitric  acid,  oxalic  acid,  or  by  the  action  of  a 
ferment. 
This  acid  should  be  colorless,  and  should,  as  already  stated,  be 
entirely  volatilized  by  heat.  There  should  be  little  or  no  aroma, 
and,  if  any,  it  should  possess  an  aromatic  smell  resembling  va- 
nilla. The  benzoic  acid,  before  it  passes  from  the  manufacturer's 
hands,  is  put  up  in  one  ounce  bottles,  which  are  sometimes  made 
short  weight — a  common  practice  with  both  this  article  and  sul- 
phate of  quinine. 
Acidum  Ciiricum. 
3HO,  C12H5  On  +  HO  —  201  [C°  IP  O7  .] 
Citric  acid  is  met  with  in  two  forms — viz.,  in  colorless  right 
rhombic  prisms,  having  the  composition  2  Ci2H8  Ou  +  HO ;  this 
variety  constitutes  the  commercial  article,  and  also  another  form 
having  the  composition  2  (Ci2H8  Ou)  4-  HO,  the  water  in  this 
case  probably  being  mechanically  combined.  It  is  soluble  in 
0*75  parts  of  cold  and  in  0*5  parts  of  boiling  water ;  readily 
soluble  in  alcohol,  but  insoluble  in  ether. 
Tartaric  acid  is  the  only  adulteration  practised  with  citric 
acid.  This  fraud  is  best  determined  by  adding  a  solution  of 
acetate  of  potash  to  a  solution  of  the  citric  acid  under  examina- 
tion, each  solution  being  pretty  concentrated.  A  precipitate  of 
bitartrate  of  potash  is  produced  if  tartaric  acid  is  present. 
Sulphuric  acid,  oxalic  acid,  and  lead,  are  the  usual  impurities 
occurring. 
After  having  been  examined  for  tartaric  acid,  it  may  be  tested 
for  these  impurities  in  the  following  manner : 
1.  Lime  water  is  added  in  excess  to  a  dilute  cold  solution  of 
the  citric  acid. 
A  white  precipitate  is  indicative  of  the  presence  of  oxalic  acid. 
