﻿120 
  F. 
  TF. 
  Clarice 
  — 
  Constitution 
  of 
  Toui^maline. 
  

  

  and 
  Kalb, 
  they 
  fit 
  in 
  well 
  with 
  those 
  of 
  Riggs, 
  and 
  are 
  

   amenable 
  to 
  the 
  same 
  treatment. 
  

  

  At 
  first 
  glance, 
  some 
  of 
  the 
  formulae 
  which 
  I 
  have 
  proposed 
  

   may 
  seem 
  to 
  be 
  complex 
  ; 
  but 
  they 
  are 
  all 
  of 
  the 
  same 
  type, 
  

   and 
  can 
  be 
  reduced 
  to 
  a 
  few 
  general 
  expressions, 
  as 
  follows 
  : 
  

  

  ^SiO,E^R'3 
  ^SiO^iz^RV 
  /.SiO,-R"H 
  

  

  Al— 
  SiO, 
  = 
  Al 
  Al-SiO, 
  -i 
  Al 
  Al-SiO, 
  - 
  R'^H 
  

  

  ^SiO, 
  = 
  AlBO, 
  \SiO, 
  = 
  AlBO, 
  ^SiO, 
  = 
  AlBO, 
  

  

  AI-BO3 
  = 
  R',(R") 
  A1-B03=R',(R'') 
  A1-B03=R'^ 
  

  

  ^SiO, 
  = 
  AlBO, 
  ^SiO,=: 
  AlBO, 
  ^SiO,^. 
  AlBO, 
  

  

  Al-SiO^=Al 
  Al-SiO, 
  = 
  Al 
  Al-SiO 
  -R"H 
  

  

  ^SiO^^Al 
  \SiO,EER'3 
  \SiO, 
  = 
  R"H 
  

  

  1. 
  2. 
  3. 
  

  

  These 
  formulee 
  cover 
  all 
  of 
  the 
  established 
  variations 
  in 
  the 
  

   composition 
  of 
  tourmaline, 
  they 
  render 
  the 
  various 
  replace- 
  

   ments 
  or 
  isomorphous 
  admixtures 
  intelligible, 
  and 
  they 
  indicate 
  

   the 
  directions 
  into 
  which 
  the 
  species 
  commonly 
  alters. 
  There 
  

   is 
  one 
  objection 
  to 
  them, 
  namely, 
  that 
  one 
  of 
  the 
  end 
  products 
  

   contains 
  no 
  alkali 
  metal, 
  and 
  no 
  alkali 
  free 
  tourmaline 
  is 
  known. 
  

   The 
  same 
  objection 
  applies 
  to 
  the 
  Penfield-Foote 
  formula, 
  as 
  

   will 
  be 
  seen 
  by 
  any 
  one 
  who 
  attempts 
  to 
  apply 
  it 
  in 
  the 
  dis- 
  

   cussion 
  of 
  the 
  iron 
  tourmalines. 
  Under 
  either 
  system 
  of 
  

   formulation 
  the 
  existence 
  in 
  tourmaline 
  of 
  alkali-free 
  salts 
  

   must 
  be 
  assumed. 
  

  

  One 
  further 
  possible 
  advantage 
  in 
  the 
  proposed 
  formulae 
  

   remains 
  to 
  be 
  pointed 
  out. 
  All 
  of 
  the 
  chemists 
  who 
  of 
  late 
  

   years 
  have 
  discussed 
  the 
  composition 
  of 
  tourmaline 
  agree 
  in 
  

   adopting 
  the 
  ratio 
  between 
  silicon 
  and 
  boron 
  of 
  2 
  : 
  1, 
  or 
  ttSiO^ 
  : 
  

   B2O3. 
  And 
  yet 
  many 
  of 
  the 
  analyses 
  vary 
  from 
  this 
  ratio 
  to 
  

   an 
  extent 
  which 
  may 
  not 
  be 
  due 
  to 
  experimental 
  errors. 
  For 
  

   example, 
  from 
  among 
  Riggs' 
  analyses 
  the 
  following 
  cases 
  show 
  

   large 
  variations, 
  the 
  boron 
  being 
  too 
  low. 
  I 
  give 
  the 
  silica 
  

   and 
  boric 
  oxide 
  as 
  determined 
  ; 
  the 
  boric 
  oxide 
  as 
  calculated 
  

   from 
  the 
  silica 
  by 
  the 
  accepted 
  ratio, 
  and 
  the 
  amount 
  of 
  varia- 
  

   tion 
  between 
  the 
  two. 
  

  

  SiOo 
  B0O3 
  found. 
  B2O3 
  calc. 
  Diff. 
  

  

  Rumford, 
  red 
  38-07 
  9'99 
  IMO 
  —Ml 
  

  

  Paris, 
  black 
  35-03 
  9*02 
  10-22 
  —1-20 
  

  

  Monroe, 
  brown 
  3()-41 
  9-65 
  10-02 
  --0-97 
  

  

  Brazil, 
  green 
  .. 
  _ 
  3G-91 
  9-87 
  10-76 
  — 
  0'89 
  

  

  Auburn, 
  colorless... 
  38-14 
  10-25 
  11-12 
  —0-87 
  

  

  In 
  the 
  analyses 
  by 
  Jannasch 
  and 
  Kalb 
  the 
  following 
  exam- 
  

   ples 
  are 
  very 
  striking 
  : 
  

  

  