PROPERTIES    AND    TESTS    OF    FULLER 's    EARTH.  279 
limes  possess  some  efficiency  as  a  result  of  existing  in  a  certain 
physical  condition;  and,  second,  that  it  is  certain  that  fuller's  earth 
Ian  not  owe  more  than  a  small  part  of  its  peculiar  properties  to  the 
tresence  of  free  silicic  acid. 
I  Sloan a  makes  the  following  suggestion  concerning  the  mode  of 
Lotion  of  fuller's  earth: 
I  Fuller's  earth  is  now  extensively  employed  in  the  bleaching  of  mineral,  animal,  and 
regetable  oils  and  fats.  The  alleged  chemical  bleaching  in  the  process  is  highly  ques- 
fconable;  its  action  more  properly  involves  mechanical  entanglement  of  the  suspended  I 
loloring  matter  by  the  contained  clay  substance.     *  *     It  is  observed  that  where 
Ihe  alumina  exceeds  one-fifth  of  the  amount  of  silica  present  the  critical  point  is 
Approximated  beyond  which  an  increase  in  the-  densely  bedding  aluminous  matter 
prejudices  filtration.     The  silica  therefore  serves  to  maintain  the  required  porosity. 
Sloan  has  here  come  very  near  to  hitting  the  mark.  He  has  evi- 
dently the  right  idea  in  mind,  but  has  not  gone  deeply  enough  into 
[he  subject  to  state  it  in  detail  with  clearness.  The  propriety  of 
these  remarks  will  become  more  clearly  apparent  later  in  this  discus- 
lion;  for  the  present  I  will  only  remark  that  it  is  important  that 
the  term  "clay  substance"  be  taken  in  its  more  general  significance 
and  not  as  synonymous  with  kaolin.  Also,  I  must  tal  e  exception  to 
the  implied  statement  that  the  bleaching  power  is  dependent  on  and 
proportional  to  the  alumina  in  the  earth,  as  I  have  found  that  up  to 
a  certain  point  removal  of  the  alumina  is  actually  beneficial  to  the 
pfficiency  of  the  earth.     (See  results  8,  10,  and  11,  Table  5.) 
I  see  no  other  suggestions  as  to  the  mode  of  action  of  fuller's  earth 
proposed  in  any  of  the  literature,  but  it  is  possible  that  some  may 
consider  extreme  fineness  of  grain  an  explanation,  and  it  may  be 
worth  while  to  combat  this  idea.  Wheeler,  I  believe,  has  shown  that 
most  clays  (and  other  minerals?)  have  some  slight  bleaching  power, 
if  very  finely  powdered,  but  no  one  has  been  able  to  procure  any 
appreciable  efficiency  by  such  means.  The  few  experiments  I  have 
made  have  given  practically  negative  results,  and,  as  shown  later, 
any  very  slight  increase  in  efficiency  can  be  readily  explained. 
Finally,  it  can  be  easily  seen  that  it  would  be  very  difficult  to  explain 
the  peculiar  effects  of  acid  on  fuller's  earth  on  the  assumption  that 
its  bleaching  action  is  due  primarily  to  fineness. 
In  concluding  this  division  the  following  quotation6  seems  of  inter- 
est. The  authors  are  chemists  of  the  United  States  Internal-Revenue 
Office  and  undoubtedly  have  excellent  facilities  for  consulting  chem- 
ical literature. 
The  color-absorbing  power  of  fuller's  earth  is  a  most  interesting  subject  which  does 
not  appear  to  have  been  investigated  to  any  extent.  Whether  it  is  due  to  chemical 
or  physical  action,  and  the  connection,  if  any,  between  the  composition  of  the  earth 
o  Sloan,  Earle,  Preliminary  Report  on  Clays  of  South  Carolina,  South  Carolina  Geol. .Survey,  1904, 
pp.  59-61. 
b  Crampton,  C  A.,  and  Simons,  F..D.,  Detection  of  caramel  in  spirits  and  vinegar:  Jour  Am.  Chem. 
Soc,  vol.  21,   1899,  p.  355. 
