416 
ON  GLUCOSE. 
them, -called  Tromraers'  test,  is  as  follows  :  Add  caustic  potash, 
and  filter  if  necessary,  then  dilute  solution  of  sulphate  of  copper 
in  small  quantities ;  the  precipitate  that  first  forms  dissolves  on 
stirring,  and  the  solution  becomes  azure  blue,  but  after  standing, 
a  fawn  colored  precipitate  of  suboxide  of  copper  will  be  formed. 
The  conditions  and  precautions  to  be  observed  are  fully  given  in 
medical  vforks  and  need  not  be  repeated  here.  The  property  of 
grape  sugar  to  reduce  metallic  salts  is  made  use  of /or  the  prepa- 
ration of  silver  mirrors.  Add  to  the  nitrate  of  silver  a  few  drops 
of  ammonia  and  then  some  grape  sugar,  and  the  metal  will  be 
precipitated. 
Chloride  of  silver  can  also  be  reduced  by  grape  sugar,  and  this 
method  affords  a  way  for  reclaiming  photographic  wastes,  and  of 
preparing  pure  metallic  silver.  Take  14  parts  of  well  washed 
and  still  moist  chloride  of  silver,  24  parts  of  caustic  soda,  sp.  gr. 
1-333,  llj  parts  ammonia,  sp.  gr.  0-925  ;  to  this  add,  with  con- 
stant agitation  in  a  flask,  7|-  parts  pure  honey,  or  9J  parts  grape 
sugar  syrup,  and  let  the  mixture  stand  in  a  warm  place  until 
sulphuretted  hydrogen  affords  no  sign  of  silver.  Decant  and 
wash  out  all  traces  of  chlorine.  The  reduced  silver  can  then  be 
dried  and  melted  in  a  crucible. 
Platinum  black,  finely  divided  metallic  platinum,  can  be  ob- 
tained from  the  chloride  by  adding  carbonate  of  soda  in  excess, 
and  heating  the  solution  for  ten  minutes.  The  precipitate  can 
be  collected  in  a  filter,  and  then  well  washed  and  dried. 
Grape  sugar  crystallizes  in  warty,  cauliflower  concretions 
composed  of  hard  transparent  cubes.  It  is  less  soluble  in  water 
than  cane  sugar,  but  more  soluble  in  alcohol.  Two  and  a  half 
parts  of  glucose  are  required  to  produce  the  same  sweetening 
effect  as  one  part  of  cane  sugar.  Sulphuric  acid  does  not  de- 
compose it,  but  forms  a  definite  acid  with  it,  called  sulpho  sac- 
charic acid.    It  forms  a  double  salt  with  common  salt. 
NaCl,2(Cl^ff^Ol^)+2aq. 
It  also  forms  definite  but  unstable  combinations  with  the  al- 
kaline bases. 
From  the  foregoing  it  will  be  apparent  that  grape  sugar  can 
be  easily  and  cheaply  prepared,  and  that  it  is  capable  of  many 
important  uses  in  the  arts  if  it  could  be  manufactured  in  ade- 
quate quantity  and  at  a  reasonable  rate. — Journ.  of  Applied 
Chemistry,  New  York,  June,  lS10. 
