Ajauwy,^9T5.m'}   Development  of  the  Sugar  Industry.  19 
the  evaporating  solution  in  the  first  effect  boiled  the  solution  in  the 
second,  and  the  steam  from  the  second  effect  boiled  the  solution  in  the 
third,  and  so  on.  By  increasing  the  vacuums  in  the  effects  as  the 
heating  power  of  the  steam  diminished,  it  was  found  possible  to  boil 
off  the  water  in  a  number  of  vessels  by  the  heat  which  was  supplied 
to  the  first  unit  of  the  series.  The  original  patent  of  Rillieux,  No. 
4879,  December  10,  1846,  gives  the  following  description :  "  A  series 
of  vacuum  or  partial-vacuum  pans  so  combined  together  as  to  make 
use  of  vapor  from  the  evaporation  of  the  juice  in  the  first  to  heat 
the  juice  in  the  second,  and  the  vapor  from  this  to  heat  the  juice  in 
the  third,  which  latter  is  in  connection  with  a  condenser,  the  pressure 
in  each  succeeding  one  being  less."  The  original  evaporator  of 
Rillieux  was  a  triple  effect  and  this  is  now  probably  the  most  common 
form  of  multiple  evaporator,  although  there  are  quadruple,  quintuple 
and  even  sextuple  effects.  Where  more  than  three  effects  are 
joined,  the  juice  in  the  first  unit  is  usually  boiled  under,  or  slightly 
above,  atmospheric  pressure,  in  order  to  supply  sufficient  heat  for 
carrying  through  to  the  last  member  of  the  series. 
In  1835  the  great  French  physicist,  Biot,  invented  the  polariscope, 
and  no  single  piece  of  laboratory  apparatus  has  done  more  to  advance 
the  science  of  sugar  manufacture.  It  was  possible,  now,  to  determine 
sugar  quickly  and  accurately  and  the  foundation  stone  of  chemical 
control  in  sugar  manufacture  was  thus  laid.  More  than  this,  the 
polariscope  made  it  possible  to  analyze  quickly  the  sugar  beets  used 
for  seed  selection.  By  selecting  for  seed  each  year  the  beets  of 
highest  sugar  content  the  sugar  percentage  of  the  beet  has  been 
raised  from  8.8  per  cent,  in  1838  to  18. 1  per  cent,  in  1908,  or  more 
than  doubled. 
In  1844  the  centrifugal  was  invented  by  Schotler  and  now  it 
became  possible  to  eliminate  the  molasses  from  the  magma  of  sugar 
crystals  in  a  few  minutes,  whereas  months  were  consumed  by  the 
old  process  of  drainage.  In  1853  the  filter  press  was  invented  by 
Needham  and  it  was  possible  now  for  the  first  time  to  filter  off  the 
impurities  of  the  clarified  juice  with  neatness  and  dispatch.  It  is 
thus  seen  that,  within  twenty  years,  four  great  epoch-making  inven- 
tions were  introduced  into  sugar  manufacture :  the  multiple  effect, 
the  polariscope,  the  centrifugal,  and  the  filter  press. 
The  appliance  that  we  think  of  as  most  peculiarly  connected  with 
beet-sugar  manufacture,  the  diffusion  battery,  was  of  comparatively 
late  origin  and  was  not  introduced  until  1864,  by  Jules  Robert. 
