THE  ANIMAL  CHARCOAL  USED  IN  SUGAR  REFINING.  429 
quantity.  The  author  stated  that  he  had  analysed  charcoal  con- 
taining 2J  per  cent,  of  the  salt,  and  that  the  usual  amount  in 
old  char  is  from  half  to  three-quarter  per  cent.,  but  that  in  ex- 
treme cases  it  may  be  present  in  Clyde  charcoal  to  the  extent  of 
1  per  cent.  The  carbonate  of  lime  present  in  some  hard  waters 
is  also  absorbed  by  the  charcoal. 
The  author  briefly  considered  the  offices  fulfilled  by  the  vari- 
ous ingredients  of  the  charcoal.  Animal  charcoal  has  great 
power  of  absorbing  gases,  coloring  matters,  and  such  mineral 
salts  as  are  but  slightly  soluble  in  water.  The  removal  of  col- 
oring matter  is  the  chief  object  in  view  ;  but  gummy  and  other 
extractive  matters  have  also  to  be  removed.  Animal  charcoal 
extracts  them  both  with  equal  facility.  The  author  finds  that 
it  readily  absorbs  ordinary  egg  albumen  and  gum,  and  he  thinks 
that  the  circumstance  that  each  of  these  bodies  has  an  insoluble 
modification  may  have  something  to  do  with  their  absorption  by 
the  charcoal.  Iron  is  readily  removed  from  sugar  liquors  by 
passing  them  through  a  cistern  of  new  char.  It  is  the  nitroge- 
nous carbon  which  is  the  most  powerful  decolorising  ingredient 
of  the  char,  for  if  the  char  be  burnt  perfectly  white,  on  the  sur- 
face and  without,  it  does  not  remove  the  slightest  trace  of  col- 
oring matter.  This  fact  the  author  has  demonstrated  by  actual 
experiment :  it  is  with  him  no  mere  opinion. 
The  highly  porous  carbon  is  not  the  only  useful  ingredient^ 
although  it  is  essentially  the  decolorising  agent.  Carbonate  of 
lime  is  also  of  use  in  neutralising  the  small  proportion  of  free 
acid  present  in  almost  all  sugars  except  beet ;  and  it  is  still 
more  important  in  neutralizing  the  lactic  and  other  acids  formed 
in  the  weak  liquors,  by  a  process  of  fermentation  which  it  is 
difficult  to  prevent.  Hence  charcoal  deprived  of  its  carbonate 
of  lime  is  objectionable,  and  its  use  is  certain  to  produce  sour 
liquors  and  give  rise  to  the  presence  of  iron  in  the  low-class 
sugars.  As  the  water  of  Greenock  and  Glasgow  contains  only 
traces  of  carbonate  of  lime,  the  quantity  of  that  salt  naturally 
present  in  charcoal  gradually  lessens,  until  in  pretty  old  char 
it  is  sometimes  reduced  to  about  1J  per  cent.  In  refineries  con- 
ducted on  scientific  principles  the  amount  is  never  suffered  to 
fall  so  low.    If  it  falls  below  2-J  per  cent.,  sour  liquors  are  sure 
