248 
ON  THE  COPPEE  TEST  FOR  SUGAR. 
ther  red  precipitate  after  several  minutes'  boiling,  is  the  alone 
criterion  of  the  exhaustion  of  the  sugar,  which  is  just  the  inverse 
of  the  present  method.  The  filtered  blue  liquid  may  be  again 
rendered  available  for  other  reductions  by  concentration  or  evap- 
oration down  to  about  the  tone  of  the  original  copper  solution 
used.  The  following  is  the  formula  by  which  I  make  the  solu- 
tion of  copper : — Sulphate  of  copper,  half-a  drachm  ;  distilled 
water,  three  ounces.  Dissolve  by  heat,  then  add,  tartaric  acid, 
half-a  drachm ;  and,  when  cool,  caustic  potash,  one  and  a-half 
drachms  ;  and,  lastly,  pure  carbonate  of  potash,  one  and  a-half 
drachms.  An  ounce  of  this  liquor  boiled  with  half-a-grain  of 
grape  sugar,  dissolved  in  a  little  water,  gave  a  scarlet  red  pre- 
cipitate of  one  and  a-half  grains,  every  three  parts  representing 
one  of  sugar.  The  ~gth  part  of  a  grain  of  sugar  produces  a 
decided  precipitate.  Diabetic  urine  ought  to  be  purified  by  pre- 
cipitation with  excess  of  sugar  of  lead,  and  any  remaining  lead 
thrown  out  by  passing  a  stream  of  sulphide  of  hydrogen,  the 
liquid  filtered  and  evaporated  to  about  half  its  bulk  previous  to 
applying  the  cupreous  liquor  ;  but  if  the  quantity  of  lead  salt  be 
nicely  adjusted,  there  will  be  no  necessity  for  using  the  gas. 
High-colored  urine,  supposed  to  contain  sugar,  requires,  in  ad- 
dition to  the  precipitation  by  lead,  to  be  decolorised  by  animal 
charcoal,  and  before  using  the  test  any  lime  which  may  have 
been  acquired  from  the  charcoal  should  be  extracted  by  boiling 
the  filtrate  with  a  little  carbonate  of  potash  and  filtering.  Such 
urine  will  not  afford,  like  true  diabetic  urine,  a  red  precipitate, 
but  a  muddy,  yellow  one,  if  sugar  exists  at  all,  and  the  filtered 
liquid,  instead  of  being  blue,  will  be  yellowish  green. 
Although  it  has  been  stated,  on  the  authority  of  Brucke  and 
others,  that  sugar  obtains  in  ordinary  or  healthy  urine,  I  have 
not  been  able  to  verify  it  by  tests,  owing  probably  to  not  hav- 
ing operated  on  a  sufficiently  large  quantity.  The  only  way  of 
proving  it,  I  presume,  would  be  by  carefully  evaporating  to  an 
extract  the  purified  urine  and  adopting  the  fermentation  process. 
—  Chem.  News,  London,  Nov.  30,  1861. 
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