﻿24 
  Becker 
  — 
  Some 
  Queries 
  on 
  Rock 
  Differentiation. 
  

  

  towards 
  the 
  bottom, 
  so 
  that 
  a 
  concentration 
  of 
  the 
  substance 
  in 
  

   solution 
  occurs 
  in 
  the 
  lower 
  portion. 
  This 
  fact 
  appears 
  to 
  have 
  

   been 
  observed 
  first 
  by 
  Mr. 
  (X 
  Ludwig 
  in 
  1856* 
  and 
  was 
  subse- 
  

   quently 
  studied 
  by 
  Mr. 
  Ch. 
  Soret.f 
  The 
  phenomenon 
  has 
  

   been 
  explained 
  by 
  Mr. 
  van't 
  Hoff.J 
  The 
  osmotic 
  pressure 
  of 
  

   a 
  substance 
  in 
  solution 
  is 
  proportional 
  to 
  the 
  absolute 
  tempera- 
  

   ture. 
  Hence 
  there 
  is 
  a 
  resultant 
  pressure 
  in 
  an 
  unequally 
  

   heated 
  fluid 
  which 
  is 
  directed 
  towards 
  the 
  cooler 
  portion, 
  and 
  

   this 
  will 
  not 
  be 
  equilibrated 
  until 
  the 
  osmotic 
  pressure 
  in 
  the 
  

   cooler 
  portion 
  is 
  appropriately 
  increased. 
  Now 
  the 
  osmotic 
  

   pressure 
  is 
  proportional 
  to 
  the 
  concentration 
  as 
  well 
  as 
  to 
  the 
  

   temperature 
  ; 
  and 
  the 
  condition 
  of 
  equilibrium 
  is 
  therefore 
  

   that 
  the 
  concentrations 
  should 
  be 
  inversely 
  as 
  the 
  absolute 
  

   temperatures. 
  Thus 
  if 
  a 
  magma 
  were 
  heated 
  to 
  T 
  = 
  1500° 
  at 
  

   the 
  top 
  while 
  the 
  bottom 
  of 
  the 
  mass 
  were 
  kept 
  at 
  T 
  = 
  1400°, 
  

   the 
  concentration 
  of 
  the 
  substances 
  dissolved 
  in 
  the 
  magma 
  

   would 
  increase 
  until 
  that 
  at 
  the 
  bottom 
  were 
  15/14 
  = 
  1*07 
  of 
  

   that 
  at 
  the 
  top. 
  Mr. 
  van't 
  Hoff's 
  theory 
  of 
  this 
  case 
  agrees 
  

   somewhat 
  roughly 
  but 
  substantially 
  with 
  Mr. 
  Soret's 
  experi- 
  

   ments. 
  

  

  The 
  solution 
  of 
  any 
  substance 
  in 
  a 
  fluid 
  is 
  attended 
  by 
  a 
  

   change 
  in 
  the 
  total 
  volume. 
  When 
  this 
  change 
  is 
  a 
  decrease 
  

   in 
  volume, 
  solubility 
  increases 
  with 
  increasing 
  pressure 
  ; 
  and 
  

   vice 
  versa. 
  Hence 
  in 
  a 
  deep 
  mass 
  of 
  solution 
  of 
  constant 
  

   temperature 
  there 
  is 
  believed 
  to 
  be 
  a 
  tendency 
  to 
  concentration 
  

   through 
  pressure 
  at 
  the 
  bottom 
  or 
  the 
  top 
  of 
  the 
  mass. 
  The 
  

   change 
  of 
  concentration, 
  however, 
  would 
  be 
  so 
  small 
  that 
  

   physicists 
  are 
  not 
  hopeful 
  of 
  demonstrating 
  it 
  experimentally. 
  

   The 
  thermodynamical 
  discussion 
  of 
  Messrs. 
  Gouy 
  and 
  Chap- 
  

   eron§ 
  seems 
  to 
  show 
  that 
  even 
  in 
  vessels 
  100 
  meters 
  in 
  depth 
  

   the 
  effect 
  of 
  gravity 
  on 
  sodium 
  chloride 
  solution 
  would 
  influ- 
  

   ence 
  concentration 
  only 
  to 
  the 
  extent 
  of 
  a 
  fraction 
  of 
  1 
  per 
  

   cent, 
  the 
  concentration 
  being 
  greater 
  at 
  the 
  bottom. 
  It 
  is 
  

   evident 
  that 
  the 
  process 
  by 
  which 
  concentration 
  is 
  effected 
  is 
  

   molecular 
  flow. 
  Further 
  remarks 
  on 
  the 
  variability 
  of 
  solu- 
  

   bility 
  with 
  pressure 
  will 
  be 
  made 
  in 
  discussing 
  the 
  properties 
  

   of 
  immiscible 
  fluids. 
  

  

  There 
  is 
  no 
  question 
  that 
  molecular 
  flow 
  does 
  play 
  a 
  part 
  in 
  

   lithogenesis. 
  One 
  may 
  often 
  see 
  blebs 
  or 
  smears 
  of 
  matter 
  in 
  

   either 
  granular 
  or 
  porphyritic 
  rocks 
  which 
  have 
  manifestly 
  

   undergone 
  at 
  least 
  superficial 
  solution, 
  the 
  rock 
  around 
  the 
  bleb 
  

   showing 
  an 
  aureole 
  of 
  diffusion. 
  So, 
  too, 
  crystallization 
  in 
  

   many 
  cases 
  is 
  explicable 
  only 
  by 
  the 
  molecular 
  flow 
  of 
  a 
  cer- 
  

  

  *Wien 
  Sitz. 
  Ber., 
  vol, 
  xx, 
  1856, 
  p. 
  539. 
  

   f 
  Comptes 
  Rendus, 
  Paris, 
  vol. 
  xci, 
  1880, 
  p. 
  289. 
  

   % 
  Zeitschr. 
  phys. 
  Chem 
  , 
  vol. 
  i, 
  1887, 
  p. 
  487. 
  

   § 
  Ann. 
  de 
  ch: 
  phys. 
  (VI), 
  vol. 
  xii, 
  1887, 
  p. 
  384. 
  

  

  