﻿upon 
  Natrolite, 
  Scolecite, 
  Prehnite 
  and 
  Pectolite. 
  349 
  

  

  SiO 
  

  

  Analysis. 
  

  

  42-31 
  

  

  19-95 
  

  

  6-20 
  

  

  none 
  

  

  26-63 
  

  

  5-02 
  

  

  Fractional 
  water. 
  

   At 
  100° 
  

  

  •21 
  

  

  Al 
  0, 
  . 
  . 
  . 
  

  

  At 
  180° 
  .._ 
  

  

  •18 
  

  

  Fe 
  O 
  ._. 
  

  

  At 
  250° 
  

  

  •10 
  

  

  FeO 
  .... 
  

  

  At 
  350° 
  

  

  •11 
  

  

  CaO 
  .... 
  

   H,0 
  .... 
  

  

  Incipient 
  red 
  heat. 
  . 
  

  

  Full 
  red 
  heat 
  

  

  Over 
  blast 
  

  

  •28 
  

  

  4-05 
  

  

  •09 
  

  

  

  100-11 
  

  

  

  Total 
  

  

  5-02 
  

  

  "With 
  sodium 
  carbonate 
  solution, 
  0*38 
  per 
  cent 
  of 
  silica 
  was 
  

   extracted 
  from 
  the 
  fresh 
  mineral. 
  From 
  the 
  ignited 
  prehnite, 
  

   1-22 
  per 
  cent 
  was 
  taken 
  out. 
  Very 
  little 
  silica, 
  therefore, 
  is 
  

   liberated 
  by 
  ignition. 
  

  

  Two 
  determinations 
  were 
  made 
  of 
  the 
  action 
  of 
  ammonium 
  

   chloride, 
  as 
  follows 
  : 
  

  

  A. 
  Heated 
  8 
  hours. 
  On 
  leaching 
  with 
  water, 
  1*31 
  per 
  cent 
  of 
  

  

  lime 
  and 
  0*17 
  of 
  alumina 
  dissolved. 
  

  

  B. 
  Heated 
  12 
  hours. 
  1*41 
  per 
  cent 
  of 
  lime 
  was 
  extracted, 
  and 
  in 
  

  

  the 
  washed 
  residue 
  0*22 
  per 
  cent 
  of 
  ammonia 
  was 
  found. 
  

  

  Prehnite, 
  therefore, 
  differs 
  widely 
  from 
  natrolite 
  and 
  scole- 
  

   cite 
  in 
  its 
  behavior 
  with 
  ammonium 
  chloride. 
  Yery 
  little 
  

   action 
  takes 
  place, 
  even 
  upon 
  long 
  heating 
  to 
  350° 
  in 
  a 
  sealed 
  

   tube, 
  and 
  practically 
  no 
  ammonia 
  is 
  absorbed. 
  The 
  water 
  is 
  

   more 
  firmly 
  held 
  than 
  was 
  the 
  case 
  with 
  the 
  other 
  two 
  minerals, 
  

   and 
  is 
  almost 
  certainly 
  to 
  be 
  regarded 
  as 
  constitutional. 
  The 
  

   orthosilicate 
  formula 
  for 
  prehnite 
  is 
  unaffected 
  by 
  these 
  results, 
  

   and 
  may 
  stand 
  as 
  fairly 
  probable. 
  Prehnite 
  cannot 
  be 
  corre- 
  

   lated 
  with 
  natrolite 
  and 
  scolecite 
  on 
  any 
  basis 
  of 
  similar 
  chem- 
  

   ical 
  structure. 
  

  

  Pectolite. 
  

  

  In 
  the 
  first 
  paper 
  of 
  this 
  series* 
  we 
  described 
  a 
  number 
  of 
  

   experiments 
  upon 
  pectolite, 
  in 
  which 
  we 
  showed 
  that 
  it 
  was 
  

   almost 
  undoubtedly 
  a 
  metasilicate 
  ; 
  but 
  the 
  action 
  of 
  ammo- 
  

   nium 
  chloride 
  upon 
  it 
  was 
  neglected, 
  as 
  having 
  been 
  studied 
  

   already 
  by 
  Schneider 
  and 
  Clarke.f 
  In 
  their 
  experiments 
  

   upon 
  pectolite 
  from 
  Bergen 
  Hill, 
  which 
  was 
  nearly 
  identical 
  

   in 
  composition 
  with 
  our 
  sample, 
  a 
  triple 
  heating 
  in 
  an 
  open, 
  

   crucible 
  with 
  ammonium 
  chloride 
  removed 
  20-50 
  per 
  cent 
  of 
  

   lime, 
  6*95 
  of 
  soda, 
  and 
  0'54 
  of 
  manganous 
  oxide 
  ; 
  or 
  about 
  

   two-thirds 
  of 
  the 
  total 
  amount 
  of 
  bases 
  present. 
  In 
  our 
  last 
  

   paper 
  we 
  reported 
  a 
  preliminary 
  experiment 
  by 
  the 
  sealed 
  tube 
  

   method, 
  and 
  found 
  that 
  20*72 
  per 
  cent 
  of 
  lime 
  and 
  646 
  of 
  

  

  * 
  This 
  Journal, 
  October, 
  1899. 
  

  

  f 
  Bulletin 
  No. 
  113, 
  U. 
  S. 
  Geological 
  Survey, 
  p. 
  34. 
  

  

  