ON  THE  EXTRACTION  OF  POTASSA  FROM  MARL.  239 
self  in  New  Jersey,  the  material  for  furnishing  a  cheap  supply 
of  the  acid  exists  ;  in  the  sulphuret  of  iron,  which  is  widely  dis- 
seminated throughout  certain  sections  of  it,  or  in  those  com- 
pounds of  iron  or  of  alumina  and  iron  with  sulphuric  acid, 
which  give  those  properties  so  injurious  to  vegetation  to  the  so- 
called  "  poison,"  or  4<  burning  marls." 
The  state  of  combination  in  which  the  ingredients  of  green 
sand  exist  in  it,  has  been  considered  to  be  that  of  silicates. 
Pelouze  has  called  attention  to  the  power  which  sulphates  of 
lime  has  in  decomposing  glass,  a  mixture  of  various  silicates. 
With  a  view  to  ascertain  whether  sulphate  of  lime  would  have 
any  effect  in  removing  potassa  from  the  green  sand,  50  grains 
of  it,  100  of  green  sand,  and  4  oz.  water  were  mixed  together, 
and  allowed  to  remain  in  contact  two  or  three  days.  Upon 
evaporating  the  liquid  to  dryness,  6.31  grains  of  solid  matter 
were  obtained,  which  contained  only  .06  gr.  of  potassa,  about 
th  of  the  amount  existing  in  the  quantity  used,  the  re- 
mainder being  principally  sulphate  of  lime. 
When  green  sand  is  treated  with  quicklime  and  water,  a  very 
small  amount  of  potassa  is  obtained.  100  grains  quicklime, 
100  grains  green  sand,  and  4  oz.  water  were  mixed  together, 
and  after  standing  in  contact  for  seventy-two  hours,  the  liquid 
was  evaporated  to  dryness.  The  solid  matter  obtained  weigh- 
ing 5f  grains  contained  but  .04  gr.  of  potassa;  alumina,  pro- 
toxide of  iron,  and  carbonate  of  lime  constituting  the  remain- 
der. 
The  form  of  combination  in  which  the  silica,  the  iron,  and 
the  other  ingredients  exist  in  the  green  sand  has  not  been  fully 
determined.  This  substance  has  been  regarded  as  essentially 
a  protosilicate  of  iron.  But  I  have  noticed  that,  upon  treating 
the  grains  with  acid,  without  powdering  them,  after  the  green 
portion  of  them  is  entirely  dissolved,  the  silica  is  left  behind  in 
the  form  of  small,  white  grains,  of  the  same  shape  as  the  origi- 
nal grains,  and  not  in  that  state  of  fine  division  in  which  it 
would  be  if  it  had  just  been  liberated  from  a  state  of  combina- 
tion. These  grains  of  silica,  after  ignition,  are  readily  soluble 
in  a  cold  solution  of  potassa,  from  which  facts  it  is  inferred  that 
the  silica  has  not  been  combined  with  iron,  &c,  as  a  silicate; 
and  that  the  green  sand  should  not  be  considered  as  a  mixture 
of  various  silicates.    Whether  these  ingredients  are  in  a  state 
