ON  GLUCOSE. 
411 
several  ways,  and  that  it  was  always  the  product  of  the  germina- 
tion of  starch  grains,  and  sometimes  occurred  already  formed  in 
nature. 
It  is  probable  that  both  cane  and  grape  sugar  are  formed  from 
the  starch  contained  in  the  cellular  tissues  of  the  plant,  cane 
sugar  being  formed  first,  and  then  grape  sugar,  if  acids  be 
present.  Acidulous  fruits  contain  only  grape  sugar,  whereas 
cane  sugar  occurs  in  those  that  are  free  from  stronger  acids. 
The  chief  natural  sources  of  the  grape  sugar  are  in  the  sap  of 
the  grapevine,  in  plums,  cherries,  figs,  honey,  in  the  liver  and 
in  diabetic  urine  ;  but  it  would  not  be  economical  to  prepare  it 
from  any  of  these  sources. 
One  of  the  latest  methods  for  the  preparation  of  grape  sugar 
is  the  one  proposed  by  Maubre,  and  is  as  follows  :  The  mixture 
of  dilute  sulphuric  acid  and  starch  meal  is  boiled  under  pressure 
of  six  atmospheres.  The  necessary  boilers  are  similar  to  those 
used  for  high  pressure  engines,  and  are  lined  with  lead  and  pro- 
vided in  the  interior  with  a  perforated  lead  tube  for  the  passage 
of  steam.  The  boiler  is  further  furnished  with  safety  valve,  stop 
cocks;  thermometers,  &c.  In  the  process  of  manufacture  56 
pounds  of  sulphuric  acid  of  66°  B.  are  diluted  with  5,600  pounds 
water,  and  heated  to  212°  F.  A  mixture  of  the  same  amount  of 
acid  and  water  is  made  in  a  separate  wooden  vessel,  the  heat  of 
which  is  raised  to  86°  F.  Into  the  second  mixture  2,240  pounds 
of  starch  meal  are  well  stirred  and  heated  to  100°  F.  This  is 
gradually  added  to  the  first  mixture,  and  after  heating  with  open 
valves  for  a  few  minutes  to  212°  F.,  the  stop  cocks  are  all  closed 
and  the  heat  raised  to  320°  F.  and  continued  until  all  of  the 
starch  is  converted  into  sugar,  which  requires  from  two  to  four 
hours. 
The  contents  of  the  boiler  are  then  run  into  a  wooden  tank 
and  168  pounds  of  pure  chalk  or  carbonate  of  lime,  previously 
stirred  up  with  500  pounds  of  water,  is  gradually  added  to  neu- 
tralize the  acid  ;  the  gypsum  is  caught  on  a  filter  and  the  filtrate 
evaporated  to  20°  B.,  and  afterward  clarified  by  blood  and  bone 
black  and  again  filtered.  In  this  way  the  product  is  obtained 
pure  and  free  from  bitter  and  empyreumatic  taste,  and  is  well 
suited  for  any  of  the  purposes  to  which  grape  sugar  is  adapted. 
Another  way  is  to  convert  the  starch  into  sugar  by  means  of 
