﻿22 
  Becker 
  — 
  Some 
  Queries 
  on 
  Rock 
  Differentiation. 
  

  

  at 
  one 
  temperature 
  tend 
  to 
  separate 
  at 
  some 
  other 
  temperature 
  

   into 
  two 
  or 
  more 
  immiscible 
  fluids, 
  or 
  into 
  a 
  fluid 
  portion 
  and 
  

   a 
  solid 
  one. 
  There 
  seem 
  to 
  be 
  no 
  other 
  conceivable 
  ways 
  in 
  

   which 
  segregation 
  or 
  differentiation 
  under 
  purely 
  physical 
  

   influences 
  can 
  take 
  place, 
  and 
  it 
  is 
  one 
  of 
  the 
  purposes 
  of 
  this 
  

   paper 
  to 
  examine 
  the 
  mechanism 
  of 
  these 
  processes 
  in 
  the 
  

   light 
  of 
  the 
  modern 
  conclusions 
  of 
  chemical 
  physics. 
  

  

  It 
  will 
  be 
  most 
  convenient 
  to 
  consider 
  first 
  those 
  cases 
  in 
  

   which 
  only 
  miscible 
  liquids, 
  or 
  liquids 
  present 
  only 
  in 
  miscible 
  

   proportions, 
  are 
  concerned, 
  reserving 
  consideration 
  of 
  immisci- 
  

   bility 
  and 
  insolubility 
  for 
  subsequent 
  discussion. 
  

  

  The 
  differentiation 
  of 
  a 
  homogeneous 
  magma, 
  or 
  its 
  segrega- 
  

   tion 
  into 
  distinct 
  though 
  related 
  miscible 
  fluids, 
  involves 
  rela- 
  

   tive 
  movement 
  of 
  the 
  particles 
  of 
  the 
  magma. 
  This 
  movement 
  

   cannot 
  take 
  place 
  in 
  visible 
  streams 
  or 
  currents, 
  such 
  as 
  would 
  

   result 
  from 
  convection 
  ; 
  for 
  if 
  a 
  tendency 
  to 
  segregation 
  

   existed, 
  stirring 
  would 
  neutralize 
  or 
  overcome 
  it. 
  Segregation 
  

   might, 
  however, 
  be 
  accomplished 
  by 
  what 
  may 
  be 
  called 
  

   molecular 
  flow, 
  this 
  term 
  being 
  understood 
  to 
  mean 
  the 
  pro- 
  

   gressive 
  translation 
  of 
  portions 
  of 
  a 
  liquid, 
  molecule 
  by 
  mole- 
  

   cule, 
  among 
  the 
  similar 
  or 
  dissimilar 
  molecules 
  of 
  the 
  remainder 
  

   of 
  the 
  liquid. 
  

  

  Instances 
  of 
  'molecular 
  flow. 
  — 
  Molecular 
  flow 
  is 
  exhibited 
  

   in 
  ordinary 
  diffusion, 
  in 
  osmosis, 
  and 
  in 
  some 
  cases 
  of 
  the 
  

   segregation 
  of 
  fluids. 
  Although 
  these 
  are 
  seemingly 
  very 
  dif- 
  

   ferent 
  manifestations, 
  they 
  are 
  all 
  reducible 
  to 
  the 
  tendency 
  

   which 
  fluids 
  exhibit 
  to 
  attain 
  a 
  condition 
  of 
  stable 
  equilibrium, 
  

   through 
  an 
  equalization 
  of 
  the 
  partial 
  pressures 
  of 
  each 
  com- 
  

   ponent 
  in 
  different 
  parts 
  of 
  the 
  fluid. 
  

  

  If 
  two 
  liquids 
  which 
  are 
  miscible 
  in 
  all 
  proportions 
  but 
  are 
  

   chemically 
  indifferent 
  to 
  one 
  another 
  are 
  placed 
  in 
  a 
  small 
  

   closed 
  vessel 
  and 
  are 
  maintained 
  at 
  a 
  constant 
  temperature, 
  

   each 
  diffuses 
  into 
  the 
  other, 
  and 
  the 
  flow 
  of 
  molecules 
  will 
  

   never 
  cease 
  until 
  the 
  mixture 
  is 
  uniform 
  throughout, 
  so 
  that 
  

   each 
  liquid 
  occupies 
  the 
  volume 
  formerly 
  occupied 
  by 
  both. 
  

   If 
  two 
  such 
  liquids 
  are 
  each 
  soluble 
  in 
  a 
  third, 
  each 
  will 
  diffuse 
  

   into 
  the 
  solvent 
  at 
  its 
  own 
  peculiar 
  rate, 
  and 
  in 
  such 
  cases 
  mere 
  

   diffusion 
  produces 
  partial 
  separation 
  of 
  the 
  dissolved 
  sub- 
  

   stances. 
  At 
  any 
  given 
  time 
  the 
  substance 
  which 
  diffuses 
  more 
  

   rapidly 
  will 
  be 
  found 
  in 
  greater 
  relative 
  abundance 
  at 
  any 
  

   point 
  at 
  all 
  distant 
  from 
  the 
  original 
  surface 
  of 
  diffusion. 
  

   Thus 
  Graham 
  in 
  experimenting 
  on 
  the 
  diffusion 
  in 
  water 
  of 
  a 
  

   solution 
  which 
  contained 
  5 
  per 
  cent 
  of 
  common 
  salt 
  and 
  5 
  per 
  

   cent 
  of 
  sodium 
  sulphate 
  found 
  that 
  the 
  upper 
  layer 
  of 
  water 
  

   after 
  a 
  certain 
  interval 
  contained 
  ten 
  times 
  as 
  much 
  of 
  the 
  

   chloride 
  as 
  of 
  the 
  sulphate. 
  

  

  