PURIFICATION  OF  VEGETABLE  JUICES. 
461 
cases  where  it  had  been  retained  to  a  certain  extent  in  solution, 
and  finally  procurable  at  low  cost ;  (2)  another  substance  pos- 
•sessed  of  a  (so  to  speak)  limited  oxidating  power,  which,  by  its 
own  action,  could  destroy  the  coloring  substance,  or  transform  it 
into  the  brown  substance  and  absorb  it  then, — which,  in  a  word, 
could  unite  the  qualities  of  innocuousness  and  absorbent  action 
required  in  the  substance  first  referred  to,  and  be  had  at  a  low 
cost. 
Sulphate  of  lime,  whether  natural  or  artificial  (crude  or  boiled 
plaster),  is,  of  all  bodies  which  I  have  studied,  best  fitted  to 
meet  the  first  indications.  It  is  neutral — an  essential  condition 
— has  no  action  on  sugar,  and  is  of  very  slight  solubility ;  it 
unites  to  the  conditions  of  innocuousness  and  cheapness,  the 
most  remarkable  coagulating  effects  on  the  albuminoid  sub- 
stances contained  in  the  vegetable  juices,  especially  in  that  of 
the  beet.  This  property  is  such  that  its  solution  even  an- 
swers, in  amount  relatively  very  small,  to  produce  the  effect. 
The  operation  of  defecation  can  be  executed  under  excellent 
conditions  and  with  very  little  of  the  substance ;  the  scum  becomes 
very  consistent,  collects  well,  and  the  juice  may  be  readily 
strained  in  a  condition  of  suitable  limpidity.  Sulphate  of  lime 
removes  then  perfectly  all  coagulable  substances,  but  it  does  not 
touch  the  coloring  substances,  so  that  the  juice  after  the  sepa- 
ration of  the  scum  soon  becomes  very  deeply  colored. 
Animal  black  is  almost  without  effect  immediately  after  defe- 
cation; it  only  removes  the  substance  that  has  already  oxidized, 
and  after  its  action,  the  juice  whose  color  has  been  greatly 
diminished,  is  not  slow  in  becoming  again  colored.  An  ox- 
idizing body  is  required  which  is  able  to  effect  in  a  very  short 
time  that  which  the  air  effects  but  slowly,  or  which  shall  have 
the  power  of  destroying  or  absorbing  the  substance.  Hydrated 
sesquioxide  of  iron  presents  most  the  advantageous  properties  of 
all  that  I  have  examined. 
After  all  the  coagulable  substances  have  been  removed  from 
a  saccharine  juice,  if  it  be  agitated  in  the  cold,  or  at  a  tempera- 
ture which  must  never  be  as  great  as  that  of  ebullition,  with 
hydrated  sesquioxide  of  iron,  the  filtered  liquor  will  come  through 
perfectly  colorless  and  purified  from  the  entire  presence  of  all  the 
foreign  substances  which  it  contains.    Moreover,  the  sesquiox- 
