DETERMINATION  OF  GRAPE-SUGAR,  ETC. 
83 
of  hydrate  of  potash.  On  the  other  hand,  1  grm.  of  sugar  was 
dissolved  in  40  cubic  centims.  of  water,  and  250  milligrms.  of 
concentrated  muriatic  acid  were  added  thereto ;  the  mixture 
was  then  heated  on  the  water-bath  for  ten  minutes  to  129° — 
131Q  F.  This  solution  was  then  neutralized  with  carbonate  of 
soda,  and  gradually  mixed  with  the  test-fluid  ;  of  this  99-7  cubic 
centims.  were  decolorized,  so  that  the  sugar  contained  99-7  per 
cent,  of  cane-sugar.  By  the  optical  test,  the  same  sugar  gave 
an  amount  of  99*75  per  cent,  of  cane-sugar. 
Thus  the  reagent  proved  to  be  very  accurate.  Towards  the  close 
of  the  operation,  indeed,  a  slight  yellowish  color  made  its  ap- 
pearance in  consequence  of  the  formation  of  a  concertrated  solu- 
tion of  ferrocyanide  of  potassium,  but  this  is  easily  distinguished 
from  that  produced  by  JL  th  cubic  centim.  of  the  test-fluid.  This 
coloration  is  scarcely  perceptible  when  the  sugar  is  dissolved  in 
double  the  above  quantity  of  water ;  and  also  in  tests  which  re- 
quired a  smaller  addition  of  the  test-fluid. 
To  examine  a  mixture  of  cane-sugar  and  grape-sugar,  exactly 
1  grm.  of  it  is  to  be  weighed  off  and  dissolved  in  40  cubic  cen- 
tims. of  water ;  the  solution  is  heated  to  158°  F.,  and  then  JLth 
cubic  centim.  of  the  test-fluid  is  added  from  a  graduated  tube. 
If  the  color  disappears  immediately  (as  with  the  syrups),  a  con- 
siderable quantity  of  grape-sugar  is  present,  and  entire  cubic 
centimetres  may  then  be  added,  until  the  color  slowly  disappears 
at  158°  F.,  when  the  addition  of  tenths  of  cubic  centimetres  is 
recommenced.    If  the  color  produced  by  the  last  addition  does 
not  disappear  in  15 — 20  seconds  when  shaken,  the  operation  is 
completed,  and  the  amount  of  sugar  is  then  read  off  directly,  the 
portion  of  the  test-fluid  which  was  not  decolorized  being  deduct- 
ed.   From  the  cane-sugar  indicated,  the  grape-sugar  is  calcu- 
lated in  centesimal  parts  x  according  to  the  equation 
171 :  180=  n  cubic  centimeters  :  x. 
If  the  decolorization  does  not  take  place  from  the  commence- 
ment (as  with  refined  sugars),  no  grape-sugar  is  present ;  if  it 
takes  place  slowly  (as  with  raw  sugar),  only  a  small  quantity  of 
grape-sugar  is  present,  and  the  testing  must  then  be  carried  on 
very  carefully,  as  already  described  for  the  completion  of  the 
operation. 
