PROPERTIES    AND    TESTS    OE    FULLER 's    EARTH.  289 
study  is  needed  to  determine  simple  methods  of  rational  analysis,  but 
to  judge  from  my  experiments  with  acid  treatment  it  is  not  likely  to 
be  a  difficult  problem. 
These  experiments  also  suggest  the  possibility  of  considerably 
increasing  the  bleaching  efficiency  of  fuller's  earth  by  treatment  with 
dilute  acids  or  similar  means.  There  is  no  doubt  that  this  can  be  done, 
but  further  investigations  are  needed  to  find  more  favorable  condi- 
tions and  to  show  whether  the  process  can  be  made  sufficiently  eco- 
nomical for  commercial  use.  It  is  also  probable,  as  I  have  already 
pointed  out  (p.  287),  that  fuller's  earth  may  vary  in  resistance  to  heat 
and  in  the  degree  of  dryness  needed.  A  close  study  of  this  phase  of 
the  subject  might  show  how  the  preparation  of  the  earth  affects  its 
bleaching  qualities  and  point  the  way  to  an  increased  efficiency. 
Finally,  we  come  to  the  possibility  of  creating  an  artificial  bleaching 
agent  capable  of  doing  the  work  of  fuller's  earth.  I  have  no  doubt 
whatever  that  many  common  clays  can  be  found  which  possess  a  cer- 
tain amount  of  bleaching  power  and  which  by  proper  treatment  can 
be  given  an  efficiency  equal  to  fuller's  earth.  I  am  more  skeptical  as 
to  the  practicability  of  treating  a  neutral  or  nearly  neutral  body  so  as 
to  make  it  an  efficient  bleaching  agent.  It  is  possible  that  future 
work  may  discover  some  artificial  pectoidal  body  which  will  possess  the 
same  resistance  to  drying  as  the  active  pectoids  of  fuller's  earth.  In 
that  case  I  can  see  no  reason  why  it  should  not  be  possible  to  impregnate 
a  kaolin  or  other  porous  medium  with  this  substance  and  make  of  it  an 
artificial  earth.  I  am  of  the  opinion  that  some  such  substance  may  be 
found  among  the  organic  colloids,  although  the  single  test  I  made 
along  this  line  (test  No.  41)  was  barren  of  result. 
RATIONAL    COMPOSITION    OF    FULLER' S    EARTH. 
Table  6  gives  the  approximate  rational  composition  of  the  fuller's 
earths  on  which  I  have  worked,  as  calculated  from  the  analyses  given 
in  Table  3  (p.  272).  The  calculations  are  based  on  the  percentages  of 
silica,  alumina,  and  water  soluble  and  insoluble  in  the  different 
strengths  of  acids,  and  I  believe  they  come  somewhere  near  the  truth. 
It  will  be  noticed  that  the  figures  do  not  exactly  balance  with  the  ulti- 
mate analyses,  but  they  are  probably  as  close  as  could  be  expected. 
