﻿and 
  Pseudomorpkous 
  Replacement 
  of 
  Limestone, 
  etc. 
  241 
  

  

  (26.) 
  In 
  the 
  foregoing 
  remarks 
  no 
  discrimination 
  between 
  

   limestone 
  and 
  dolomite 
  has 
  seemed 
  necessary, 
  nor 
  specific 
  refer- 
  

   ence 
  to 
  analogous 
  compounds 
  of 
  magnesium 
  in 
  isomorphous 
  

   relations 
  to 
  those 
  of 
  calcium. 
  Nor, 
  on 
  the 
  other 
  hand, 
  has 
  it 
  

   seemed 
  important 
  to 
  refer 
  to 
  relations 
  of 
  the 
  same 
  kind 
  subsist- 
  

   ing 
  between 
  corresponding 
  compounds 
  of 
  manganese 
  and 
  iron. 
  

   For 
  the 
  sake 
  of 
  brevity, 
  the 
  same 
  course 
  will 
  generally 
  be 
  

   followed 
  throughout 
  the 
  present 
  memoir. 
  Yet 
  it 
  will 
  not 
  fail 
  

   to 
  be 
  considered 
  that 
  epigenesis 
  of 
  compounds 
  of 
  manganese 
  

   is 
  practically 
  in 
  common 
  with 
  those 
  of 
  iron, 
  and 
  that 
  in 
  fact 
  

   epigenesis 
  of 
  a 
  given 
  compound 
  of 
  one 
  metal 
  often 
  involves 
  

   that 
  of 
  a 
  corresponding 
  compound 
  of 
  the 
  other. 
  Quantita- 
  

   tively 
  considered, 
  this 
  according 
  to 
  M. 
  Dieulafait* 
  appears 
  in 
  

   relative 
  degree 
  to 
  depend 
  less 
  on 
  the 
  distribution 
  of 
  the 
  two 
  

   metals 
  in 
  the 
  composition 
  of 
  silicates 
  from 
  which 
  epigenesis 
  

   proceeds, 
  than 
  might 
  be 
  supposed. 
  

  

  (27.) 
  This 
  chemist 
  observed 
  that 
  the 
  heat 
  of 
  combination 
  

   developed 
  in 
  the 
  production 
  of 
  (hydrous) 
  ferric 
  oxide 
  and 
  

   (hydrous) 
  ferrous 
  carbonate 
  from 
  ferrous 
  oxide 
  to 
  be 
  respec- 
  

   tively 
  26*6 
  and 
  10*0 
  calories 
  (Fr). 
  In 
  corresponding 
  reactions 
  

   resulting 
  in 
  the 
  production 
  of 
  manganic 
  oxide 
  (hydrate) 
  and 
  

   (hydrous) 
  manganous 
  carbonate 
  21*4 
  and 
  13*6 
  calories 
  were 
  

   developed.! 
  

  

  When 
  oxygen 
  and 
  carbonic 
  anhydride 
  both 
  in 
  excess 
  come 
  

   in 
  contact 
  with 
  minerals 
  containing 
  ferrous 
  and 
  manganous 
  

   oxides, 
  the 
  latter, 
  as 
  may 
  therefore 
  be 
  inferred, 
  will 
  be 
  con- 
  

   verted 
  into 
  ferric 
  oxide 
  (hydrate) 
  and 
  manganous 
  oxide 
  

   (hydrate) 
  and 
  no 
  carbonate 
  will 
  be 
  formed. 
  It 
  is 
  also 
  inferred 
  

   by 
  Dieulafait 
  that 
  if 
  these 
  gases 
  come 
  in 
  contact 
  with 
  the 
  

   producing 
  minerals 
  slowly 
  and 
  in 
  quantity 
  insufficient 
  to 
  trans- 
  

   form 
  both 
  oxides, 
  the 
  products 
  will 
  be 
  insoluble 
  ferric 
  oxide 
  

   (hydrate) 
  and 
  soluble 
  (hydrous) 
  manganous 
  carbonate. 
  This 
  

   serves 
  to 
  explain 
  at 
  least 
  the 
  formation 
  of 
  ferric 
  hydrate 
  

   comparatively 
  free 
  from 
  manganic 
  hydrate, 
  as 
  well 
  as 
  the 
  

   separate 
  generation 
  of 
  manganic 
  hydrate 
  comparatively 
  free 
  

   from 
  ferric 
  hydrate 
  — 
  perhaps 
  in 
  another 
  locus 
  of 
  deposition 
  

   after 
  further 
  transmission 
  of 
  solutions. 
  

  

  Again 
  it 
  is 
  inferred, 
  that 
  as 
  much 
  more 
  heat 
  is 
  developed 
  

   when 
  ferrous 
  oxide 
  is 
  converted 
  into 
  ferric 
  oxide 
  (hydrate) 
  

   than 
  when 
  converted 
  into 
  (hydrous) 
  ferrous 
  carbonate, 
  the 
  

   latter 
  can 
  be 
  formed 
  only 
  in 
  circumstances 
  where 
  atmospheric 
  

   air 
  is 
  displaced 
  by 
  reducing 
  gases 
  or 
  carbonic 
  anhydride, 
  to 
  the 
  

   exclusion 
  of 
  oxygen. 
  

  

  * 
  Comptes 
  Kendus, 
  ci, 
  609, 
  644. 
  

  

  f 
  The 
  parentheses 
  are 
  mine, 
  the 
  observer 
  ignoring 
  the 
  distinction 
  between 
  

   hydrous 
  and 
  anhydrous 
  compounds. 
  

  

  