﻿Ford 
  and 
  Bradley 
  — 
  Fyroxmangite. 
  171 
  

  

  by 
  the 
  drawing 
  table 
  method 
  of 
  Becke 
  and 
  was 
  determined 
  as 
  

   approximately 
  2Y=30°. 
  The 
  above 
  facts 
  are 
  shown 
  graph- 
  

   ically 
  in 
  fig. 
  1. 
  It 
  is 
  to 
  be 
  understood 
  that 
  because 
  of 
  the 
  lack 
  

   of 
  crystal 
  faces 
  the 
  exact 
  orientation 
  of 
  the 
  cleavage 
  pieces 
  is 
  

   Impossible, 
  and 
  therefore 
  the 
  position 
  of 
  the 
  extinction 
  direc- 
  

   tions 
  might 
  be 
  the 
  reverse 
  of 
  that 
  shown 
  in 
  the 
  figure. 
  

  

  The 
  mineral 
  was 
  intimately 
  associated 
  with 
  a 
  black 
  iron- 
  

   manganese 
  oxide, 
  a 
  description 
  of 
  which 
  will 
  be 
  found 
  beyond. 
  

   This 
  oxide 
  is 
  evidently 
  an 
  alteration 
  product. 
  The 
  material 
  

   used 
  for 
  analysis 
  was 
  selected 
  from 
  the 
  purest 
  specimen. 
  It 
  

   was 
  crushed 
  and 
  the 
  fragments 
  sifted 
  to 
  an 
  uniform 
  grain. 
  By 
  

   experimentation 
  it 
  was 
  found 
  that 
  the 
  pyroxmangite 
  was 
  not 
  

   attacked 
  by 
  hydrochloric 
  acid, 
  even 
  at 
  boiling 
  temperature, 
  but 
  

   that 
  the 
  black 
  oxide 
  was 
  completely 
  soluble 
  under 
  such 
  con- 
  

   ditions. 
  Consequently 
  the 
  powdered 
  material 
  was 
  boiled 
  in 
  

   dilute 
  hydrochloric 
  acid 
  until 
  the 
  decanted 
  acid 
  showed 
  no 
  fur- 
  

   ther 
  test 
  for 
  iron. 
  After 
  such 
  treatment 
  the 
  grains 
  of 
  pyrox- 
  

   mangite, 
  when 
  examined 
  under 
  a 
  lens, 
  appeared 
  of 
  an 
  uniform 
  

   character, 
  showing 
  bright 
  and 
  unetched 
  surfaces. 
  

  

  The 
  method 
  of 
  analysis 
  was 
  briefly 
  as 
  follows. 
  Water 
  was 
  

   determined 
  by 
  the 
  direct 
  method 
  of 
  Penfield.* 
  Silica 
  was 
  

   determined 
  as 
  usual. 
  The 
  sesquioxides 
  were 
  separated 
  by 
  the 
  

   basic 
  acetate 
  precipitation, 
  dissolved 
  in 
  nitric 
  acid 
  and 
  reprecip- 
  

   itated 
  by 
  ammonium 
  hydroxide. 
  The 
  filtrate 
  from 
  the 
  basic 
  

   acetate 
  and 
  that 
  from 
  the 
  ammonium 
  hydroxide 
  precipitations 
  

   were 
  evaporated 
  separately 
  and 
  any 
  further 
  precipitates 
  col- 
  

   lected. 
  The 
  manganese 
  was 
  precipitated 
  in 
  the 
  combined 
  

   filtrates 
  by 
  means 
  of 
  bromine 
  water, 
  dissolved 
  by 
  strong 
  sul- 
  

   phur 
  dioxide 
  water 
  and 
  again 
  precipitated 
  by 
  acid 
  sodium 
  

   phosphate. 
  Calcium 
  was 
  precipitated 
  as 
  the 
  oxalate 
  in 
  the 
  

   filtrate 
  from 
  the 
  first 
  manganese 
  precipitation. 
  No 
  magnesium 
  

   was 
  found. 
  Total 
  iron 
  and 
  alumina 
  were 
  determined 
  as 
  usual. 
  

   Careful 
  qualitative 
  tests 
  proved 
  that 
  the 
  iron 
  was 
  all 
  ferrous 
  in 
  

   valence. 
  The 
  results 
  of 
  the 
  analyses 
  by 
  Bradley 
  follow 
  : 
  

  

  

  I 
  

  

  II 
  Average 
  

  

  Eatios 
  

  

  Subtract 
  ratios 
  equivalent 
  to 
  

   EO.Al 
  2 
  3 
  .Si0 
  2 
  . 
  

  

  Si0 
  2 
  

  

  47-17 
  

  

  47-11 
  47-14 
  

  

  0-78 
  

  

  — 
  0-023 
  = 
  0-757 
  = 
  1-00 
  

  

  MnO 
  

  

  20-72 
  

  

  20-55 
  20-63 
  

  

  0-29 
  1 
  

  

  

  FeO 
  

  

  28*30 
  

  

  28-38 
  28-34 
  

  

  0'394 
  )> 
  0-717 
  

  

  — 
  0-023 
  = 
  0-694 
  = 
  0-917 
  

  

  CaO 
  

  

  1*85 
  

  

  1-91 
  1-88 
  

  

  0-033 
  J 
  

  

  

  A1.0, 
  

  

  2-50 
  

  

  2-26 
  2-38 
  

  

  0-023. 
  

  

  — 
  0-023 
  

  

  H/O 
  

  

  0-37 
  

  

  0-29 
  0-33 
  

  

  

  

  100-91 
  10050 
  100-70 
  

  

  * 
  This 
  Journal, 
  xlviii, 
  31, 
  1894. 
  

  

  Am. 
  Jour. 
  Sci.— 
  Fourth 
  Series, 
  Vol. 
  XXXVI, 
  No. 
  212.— 
  August, 
  1913. 
  

   12 
  

  

  