﻿50 
  JOURNAL 
  OP 
  THE 
  WASHINGTON 
  ACADEMY 
  OE 
  SCIENCES 
  VOL. 
  12, 
  NO. 
  3 
  

  

  fine 
  grained, 
  the 
  individual 
  crystals 
  and 
  their 
  rhombohedral 
  character 
  

   being 
  recognized 
  only 
  under 
  the 
  highest 
  magnifying 
  power 
  of 
  the 
  pet- 
  

   rographic 
  microscope. 
  The 
  probability 
  of 
  this 
  jarosite 
  containing 
  

   ammonia 
  was 
  suggested. 
  A 
  carefully 
  selected 
  sample 
  was 
  obtained, 
  

   largely 
  from 
  the 
  small 
  nodular 
  masses. 
  Treatment 
  with 
  water 
  at 
  

   room 
  temperature 
  (near 
  25° 
  C.) 
  yielded 
  0.87 
  per 
  cent 
  soluble 
  matter, 
  

   consisting 
  of 
  some 
  tschermigite, 
  together 
  with 
  a 
  small 
  quantity 
  of 
  

   jarosite, 
  and 
  a 
  trace 
  of 
  organic 
  matter. 
  If 
  it 
  be 
  considered 
  that 
  the 
  

   water-soluble 
  content 
  of 
  the 
  jarosite 
  is 
  practically 
  all 
  tschermigite 
  the 
  

   . 
  87 
  per 
  cent 
  soluble 
  matter 
  would 
  contain 
  only 
  0.05 
  per 
  cent 
  am- 
  

   monia 
  as 
  (NH4)20. 
  The 
  jarosite 
  sample 
  was 
  found 
  to 
  contain 
  1 
  .30 
  

   per 
  cent 
  (N 
  114)20, 
  which 
  when 
  corrected 
  for 
  the 
  ammonia 
  in 
  0.87 
  

   per 
  cent 
  of 
  admixed 
  tschermigite, 
  gave 
  1.25 
  per 
  cent 
  for 
  the 
  pure 
  

   jarosite. 
  A 
  lack 
  of 
  suitable 
  material 
  prevented 
  further 
  work 
  being 
  

   done 
  other 
  than 
  to 
  establish 
  quantitatively 
  the 
  presence 
  of 
  consider- 
  

   able 
  potash 
  and 
  a 
  slight 
  amount 
  of 
  soda. 
  As 
  far 
  as 
  know 
  this 
  is 
  the 
  

   first 
  recorded 
  occurrence 
  of 
  an 
  ammoniacal 
  jarosite. 
  The 
  small 
  amber 
  

   colored 
  gypsum 
  crystals 
  are 
  not 
  very 
  abundant 
  and 
  do 
  not 
  present 
  

   any 
  evidence 
  of 
  unusual 
  composition. 
  

  

  The 
  tschermigite 
  is 
  colorless 
  or 
  white 
  in 
  thick 
  masses 
  and 
  has 
  a 
  

   clear 
  glassy 
  appearance 
  in 
  small 
  pieces. 
  The 
  mineral 
  is 
  isotropic 
  and 
  

   the 
  broken 
  pieces 
  do 
  not 
  show 
  any 
  cleavage. 
  The 
  refractive 
  index 
  

   was 
  found 
  to 
  be 
  1.457 
  and 
  the 
  density 
  1.645. 
  Cornu- 
  found 
  the 
  

   density 
  of 
  the 
  Dux, 
  Bohemia, 
  tschermigite 
  to 
  be 
  1.636. 
  The 
  arti- 
  

   ficial 
  ammonium 
  alum 
  has 
  the 
  density 
  1.626. 
  The 
  value 
  1.50 
  given 
  

   for 
  tschermigite 
  in 
  Dana's 
  System 
  of 
  Mineralogy 
  is 
  obviously 
  too 
  low. 
  

  

  In 
  some 
  of 
  the 
  cavities 
  are 
  small 
  incomplete 
  crystals 
  of 
  tschermigite 
  

   and 
  some 
  of 
  the 
  columnar 
  masses 
  have 
  a 
  large 
  number 
  of 
  minute 
  

   facets 
  of 
  the 
  same 
  crystal 
  form 
  along 
  their 
  side. 
  Crystal 
  faces 
  are 
  

   also 
  present 
  on 
  top 
  of 
  parts 
  of 
  the 
  seams, 
  but 
  nowhere 
  were 
  complete 
  

   crystals 
  evident. 
  The 
  incomplete 
  crystals 
  were 
  seldom 
  larger 
  than 
  

   one 
  or 
  two 
  millimeters. 
  The 
  forms 
  noted 
  are 
  a 
  (100), 
  o(lll) 
  and 
  

   d(llO), 
  all 
  developed 
  nearly 
  equally, 
  but 
  with 
  a 
  very 
  nonequal 
  devel- 
  

   opment 
  of 
  the 
  different 
  faces 
  of 
  a 
  form 
  on 
  the 
  same 
  crystal. 
  

  

  CHEMICAL 
  COMPOSITION 
  

  

  The 
  mineral 
  readily 
  fuses 
  in 
  its 
  own 
  water 
  of 
  crystallization 
  

   below 
  the 
  boiling 
  point 
  ot 
  toluene 
  (105° 
  C). 
  It 
  is 
  easily 
  soluble 
  in 
  

   cold 
  water 
  and 
  gives 
  the 
  usual 
  reactions 
  for 
  ammonium 
  alum. 
  The 
  

  

  ^ 
  Reference 
  given 
  under 
  analysis 
  III. 
  

  

  