﻿98 
  Thibtieth 
  Repokt 
  on 
  the 
  State 
  Museum. 
  

  

  chemical 
  type, 
  by 
  admitting 
  3 
  HO 
  to 
  replace 
  Mg 
  O, 
  and 
  2 
  HO 
  

   to 
  replace 
  CuO, 
  etc. 
  These 
  cases, 
  to 
  which 
  he 
  has 
  given 
  the 
  

   name 
  of 
  polymeric 
  isomorphism, 
  are 
  but 
  instances 
  of 
  the 
  partial 
  

   substitution 
  of 
  water 
  for 
  other 
  bases 
  in 
  homologous 
  genera 
  

   which 
  differ 
  by 
  n 
  MO." 
  

  

  " 
  In 
  the 
  continuation 
  of 
  this 
  subject, 
  in 
  1854, 
  as 
  above 
  refer- 
  

   red 
  to, 
  the 
  question 
  of 
  homologies 
  was 
  further 
  illustrated 
  by 
  

   the 
  neutral 
  and 
  basic 
  nitrates 
  of 
  lead, 
  represented 
  by 
  a 
  common 
  

   formula 
  (Pb 
  2 
  2 
  ) 
  n. 
  N 
  2 
  Oi 
  . 
  These 
  salts 
  vary 
  in 
  solubility 
  and 
  

   in 
  physical 
  characters, 
  but 
  resemble 
  each 
  other 
  in 
  yielding 
  

   nitric 
  acid 
  and 
  oxide 
  of 
  lead 
  as 
  results 
  of 
  their 
  decomposition, 
  

   and 
  are 
  completely 
  analogous 
  to 
  the 
  homologous 
  series 
  of 
  Grer- 
  

   hardt, 
  which 
  differ 
  by 
  n 
  (C 
  2 
  H 
  2 
  ). 
  From 
  the 
  relation 
  between 
  

   basic 
  and 
  hydrated 
  salts, 
  the 
  same 
  view 
  is 
  to 
  be 
  extended 
  to 
  the 
  

   latter, 
  and 
  species 
  differing 
  by 
  n 
  (0 
  2 
  H 
  2 
  ) 
  and 
  n 
  (0 
  2 
  M 
  2 
  ) 
  may 
  thus 
  

   be 
  homologous. 
  The 
  above 
  formulas 
  are 
  intended 
  to 
  involve 
  

   no 
  hypothesis 
  as 
  to 
  the 
  arrangement 
  of 
  the 
  elements, 
  for 
  in 
  the 
  

   author' 
  s 
  view, 
  each 
  species 
  is 
  an 
  individual, 
  in 
  which 
  the 
  pre- 
  

   existence 
  of 
  different 
  species 
  that 
  may 
  be 
  obtained 
  by 
  its 
  

   decomposition 
  cannot 
  be 
  asserted. 
  He 
  regards 
  silicates 
  like 
  

   eudialyte, 
  sodalite, 
  and 
  pyrosmalite 
  as 
  oxychlorides, 
  (M 
  2 
  2 
  ) 
  n. 
  

   Mel, 
  and 
  nosean, 
  hauyene, 
  and 
  lapis-lazuli 
  as 
  basic 
  sulphates 
  

   (M 
  2 
  2 
  ) 
  n. 
  S 
  2 
  8 
  , 
  while 
  cancrinite, 
  and 
  perhaps 
  some 
  scapolites, 
  

   are 
  (may 
  perhaps 
  be) 
  basic 
  carbonates. 
  All 
  other 
  silicates 
  are 
  

   reducible 
  to 
  the 
  same 
  type 
  as 
  the 
  spinels, 
  n 
  (M 
  2 
  2 
  ), 
  the 
  formula 
  

   of 
  silica 
  itself 
  being 
  written 
  siO. 
  (Si 
  being 
  represented 
  by 
  

  

  one-third 
  its 
  usual 
  equivalent 
  Boric, 
  titanic, 
  tantalic, 
  and 
  

  

  niobic 
  acids 
  are 
  reduced 
  to 
  the 
  same 
  formula 
  as 
  silica." 
  

  

  " 
  Homceomorphous 
  species 
  have 
  similar 
  equivalent 
  volumes, 
  

   so 
  that 
  the 
  density 
  in 
  species 
  thus 
  related 
  enables 
  us 
  to 
  deter- 
  

   mine 
  their 
  comparative 
  equivalent 
  weights, 
  and 
  to 
  fix 
  their 
  

   positions 
  in 
  a 
  homologous 
  series. 
  The 
  proportion 
  between 
  the 
  

   silica 
  and 
  the 
  other 
  oxides 
  may 
  vary 
  greatly 
  in 
  related 
  species, 
  

   while 
  the 
  characters 
  of 
  the 
  genus 
  or 
  the 
  order 
  are 
  preserved. 
  

   This 
  is 
  illustrated 
  in 
  hornblende, 
  diopside, 
  and 
  aluminous 
  

  

  pyroxenes 
  like 
  hudsonite 
  The 
  triclinic 
  feldspars, 
  of 
  which 
  

  

  albite 
  and 
  anorthite 
  are 
  the 
  representatives, 
  furnish 
  another 
  

   example 
  ; 
  the 
  one 
  is 
  a 
  lime 
  feldspar, 
  the 
  other 
  a 
  soda 
  feldspar, 
  

   and 
  both 
  may 
  be 
  reduced 
  to 
  a 
  common 
  formula, 
  M 
  64 
  64 
  . 
  Peta- 
  

   lite, 
  a 
  lithia 
  feldspar, 
  also 
  enters 
  into 
  the 
  same 
  formula, 
  with 
  a 
  

  

  