264  MEDICAL  ANALYSIS. 
remove  the  remaining  coloring  matter,  and  lastly  the  decolorating 
power  of  the  black  is  restored  by  passing  through  it  a  solution 
of  bi-phosphate  of  lime.  It  is  to  be  hoped  that  the  high  praise 
bestowed  upon  this  process  on  the  Continent  may  induce  our 
manufacturers  to  try  it,  as  they  would  obtain  two  distinct  ad- 
vantages by  its  use.  First,  the  economy  of  operating  at  once 
upon  the  black  and  restoring  its  properties  without  removing  it 
from  the  cylinders.  Secondly,  the  prevention  of  the  noxious 
odors  given  off  during  the  revivification  of  char  by  the  ordinary 
methods.  It  is  interesting  to  note  one  of  the  results  of  the  dif- 
ferent employment  of  char  in  this  country  and  on  the  Continent. 
In  England  the  wear  and  tear  in  sugar  refinery  is  constantly 
repaired  by  the  introduction  of  fresh  char,  and  there  is  no  spent 
or  old  char  for  sale.  In  France,  on  the  contrary,  owing  to  'the 
great  impurities  in  their  beet-root  sugar  syrups,  and  to  the  use 
of  blood  in  refinery,  the  char  becomes  rapidly  clogged  with 
organic  matter,  and  is  so  completely  animalised,  that  its  value 
as  a  manure  exceeds  what  the  char  originally  cost  the  refiner. 
The  result  is  that  French  "  spent "  char  is  annually  exported  to 
the  French  colonies  to  the  amount  of  120,000  tons,  and  is  there 
used  as  a  manure  to  promote  the  growth  of  the  sugar  cane.  So 
important  is  this  article  of  commerce  considered,  that  the  French 
Government  have  appointed  special  analytical  chemists  to  deter- 
mine its  value  for  the  trade. — Lon.  Chem.  News.  July  9,  1865. 
MEDICAL  ANALYSIS;  DETERMINATION  OF  THE  PUEITY 
OF  COMMERCIAL  MEDICINES. 
By  C.  R.  C.  Tichborne,  F.  C.  S.  L. 
Acidum  Benzoicum  110.  Cuff,  03  =122.  [C7  H5  OHO.] 
Benzoic  acid  occurs  in  light  feathery  crystals,  made  by  subli- 
mation, which  appear  to  be  six-sided  prisms.  It  dissolves  in  200 
parts  of  cold  and  30  parts  of  boiling  water.  It  is  very  soluble 
in  ether  and  alcohol.  Benzoic  acid  is  seldom  adulterated  ;  when 
heated  it  sublimes  without  any  residue.  This  is  the  best  test 
that  can  be  applied.  It  was  once  stated  that  naphthaline  was 
used  to  adulterate  this  substance — the  author  never  met  with  a 
case — but  a  specimen  was  once  seen  which  was  crystallized  from 
