﻿Becker 
  — 
  Some 
  Queries 
  on 
  Hock 
  Differentiation. 
  33 
  

  

  contraction 
  of 
  volume.* 
  It 
  appears 
  to 
  follow 
  of 
  necessity 
  that 
  

   at 
  the 
  temperature 
  of 
  complete 
  miscibility 
  under 
  a 
  given 
  pres- 
  

   sure 
  an 
  increase 
  of 
  pressure 
  would 
  resolve 
  the 
  homogeneous 
  

   fluid 
  into 
  immiscible 
  portions. 
  

  

  In 
  close 
  relation 
  to 
  this 
  separation 
  of 
  a 
  homogeneous 
  fluid 
  

   into 
  different 
  layers 
  is 
  the 
  precipitation 
  of 
  a 
  solid 
  from 
  a 
  fluid. 
  

   The 
  process 
  of 
  solution 
  of 
  a 
  solid 
  is 
  one 
  involving 
  the 
  absorp- 
  

   tion 
  of 
  heat, 
  and 
  in 
  general 
  the 
  solubility 
  of 
  solids 
  increases 
  

   with 
  the 
  temperature. 
  Anomalous 
  cases 
  appear 
  to 
  be 
  referable 
  

   to 
  changes 
  in 
  molecular 
  aggregation, 
  the 
  formation 
  of 
  hydrates 
  

   and 
  like 
  causes. 
  The 
  influence 
  of 
  pressure 
  on 
  the 
  solubility 
  of 
  

   solids 
  was 
  first 
  carefully 
  investigated 
  by 
  Dr. 
  Sorbyf, 
  and 
  Mr. 
  

   F. 
  Braun+ 
  has 
  more 
  recently 
  made 
  a 
  very 
  thorough 
  study 
  of 
  

   the 
  subject. 
  Experiments 
  have 
  naturally 
  dealt 
  almost 
  exclu- 
  

   sively 
  with 
  aqueous 
  solutions 
  at 
  ordinary 
  temperatures, 
  and 
  it 
  

   must 
  be 
  borne 
  in 
  mind 
  that 
  as 
  water 
  is 
  a 
  fluid 
  of 
  very 
  excep- 
  

   tional 
  properties 
  the 
  direct 
  results 
  of 
  experiments 
  on 
  solutions 
  

   in 
  water 
  are 
  not 
  immediately 
  applicable 
  to 
  other 
  fluids 
  such 
  as 
  

   lavas. 
  Most 
  substances 
  dissolve 
  in 
  water 
  under 
  contraction 
  of 
  

   volume 
  and 
  only 
  about 
  half 
  a 
  dozen 
  compounds 
  are 
  known 
  

   which 
  undergo 
  dilatation 
  during 
  solution. 
  Xow 
  when 
  con- 
  

   traction 
  takes 
  place 
  increase 
  of 
  pressure 
  will 
  and 
  does 
  assist 
  

   solution. 
  If 
  contraction 
  were 
  a 
  universal 
  concomitant 
  of 
  solu- 
  

   tion 
  the 
  interior 
  of 
  the 
  earth 
  would 
  be 
  fluid. 
  But 
  Mr. 
  Braun 
  

   gives 
  apparently 
  sound 
  reasons 
  for 
  believing 
  that 
  even 
  in 
  aque- 
  

   ous 
  solutions 
  under 
  high 
  pressure 
  and 
  temperature, 
  dilatation 
  

   and 
  not 
  contraction 
  would 
  attend 
  solution. 
  The 
  investigations 
  

   of 
  Prof. 
  Carl 
  Barus§ 
  and 
  others 
  and 
  some 
  observations 
  of 
  mine 
  

   on 
  dikes|| 
  show 
  that 
  lavas 
  contract 
  in 
  solidifying. 
  The 
  fre- 
  

   quent 
  corrosion 
  of 
  phenocrysts 
  is 
  seemingly 
  due 
  to 
  increase 
  of 
  

   solubility 
  attending 
  relief 
  of 
  pressure. 
  Thus 
  for 
  magmas 
  it 
  

   appears 
  that 
  increase 
  of 
  pressure 
  promotes 
  precipitation 
  of 
  

   solids 
  as 
  well 
  as 
  segregation 
  into 
  distinct 
  fluids. 
  

  

  Segregation 
  by 
  immiscibility 
  . 
  — 
  In 
  fluids 
  which, 
  though 
  origi- 
  

   nally 
  homogeneous, 
  tend 
  to 
  break 
  up 
  into 
  two 
  or 
  more 
  immiscible 
  

   parts, 
  two 
  distinguishable 
  modes 
  of 
  separation 
  may 
  be 
  followed. 
  

   As 
  the 
  temperature 
  of 
  separation 
  is 
  approached, 
  the 
  walls 
  of 
  

   the 
  vessel 
  being 
  cooler 
  than 
  the 
  fluid, 
  any 
  component 
  about 
  to 
  

   separate 
  out 
  will 
  separate 
  to 
  some 
  extent 
  on 
  the 
  containing 
  

   walls 
  much 
  as 
  frost 
  or 
  dew 
  forms 
  on 
  good 
  conductors. 
  It 
  does 
  

   not 
  appear 
  that 
  any 
  large 
  part 
  of 
  a 
  large 
  mass 
  of 
  even 
  a 
  mod- 
  

   erately 
  viscous 
  fluid 
  could 
  be 
  segregated 
  in 
  this 
  way, 
  for 
  the 
  

   process 
  involves 
  molecular 
  flow 
  from 
  the 
  interior 
  of 
  the 
  fluid. 
  

  

  *Zeitsclir. 
  phys. 
  Chemie, 
  vol. 
  ix, 
  1892, 
  p. 
  469. 
  

  

  f 
  Proe. 
  R. 
  S„ 
  vol. 
  xii, 
  1863, 
  p. 
  538. 
  

  

  % 
  Wied. 
  Ann., 
  vol. 
  xxx, 
  1887, 
  p. 
  250. 
  

  

  § 
  This 
  Journal, 
  vol. 
  xliii, 
  1892, 
  p. 
  56; 
  vol. 
  xlv, 
  1893, 
  p. 
  1. 
  

  

  1 
  North 
  Amer. 
  Eev., 
  April, 
  1893. 
  

  

  Am. 
  Jour. 
  Sci.— 
  Fourth 
  Series, 
  Yol. 
  Ill, 
  No. 
  13. 
  —January, 
  1897. 
  

   3 
  

  

  