﻿28 
  Becker 
  — 
  Some 
  Queries 
  on 
  Rock 
  Differentiation. 
  

  

  water 
  would 
  contain 
  half 
  as 
  much 
  salt 
  as 
  it 
  could 
  dissolve 
  after 
  

   10,000x10,000 
  days, 
  some 
  270,000 
  years. 
  

  

  It 
  is 
  because 
  of 
  these 
  relations 
  that 
  stirring 
  is 
  so 
  efficaceous 
  

   in 
  assisting 
  solution. 
  If 
  a 
  mass 
  of 
  fluid 
  consisting 
  of 
  equal 
  

   but 
  separate 
  parts 
  of 
  concentrated 
  brine 
  and 
  water 
  were 
  so 
  

   stirred 
  that 
  the 
  streaks 
  of 
  each 
  were 
  not 
  more 
  than 
  a 
  couple 
  of 
  

   centimeters 
  in 
  thickness, 
  a 
  day 
  would 
  complete 
  by 
  diffusion 
  a 
  

   homogeneity 
  which 
  unassisted 
  diffusion 
  could 
  accomplish 
  only 
  

   after 
  hundreds 
  of 
  thousands 
  of 
  years. 
  

  

  Now 
  salt 
  (in 
  common 
  with 
  other 
  haloids) 
  is 
  a 
  highly 
  diffu- 
  

   sive 
  substance. 
  The 
  oxygen 
  salts, 
  such 
  as 
  the 
  sulphates 
  of 
  zinc, 
  

   copper 
  and 
  magnesium, 
  are 
  more 
  analogous 
  to 
  the 
  silicates 
  

   which 
  compose 
  magmas. 
  Of 
  these 
  the 
  magnesian 
  salt 
  diffuses 
  

   fastest 
  and 
  the 
  zinc 
  salt 
  the 
  slowest. 
  As 
  an 
  illustration, 
  the 
  

   copper 
  salt 
  may 
  be 
  taken. 
  Its 
  diffusivity 
  has 
  been 
  determined 
  

   by 
  Mr. 
  T. 
  Schuhmeister 
  at 
  0*00000243 
  in 
  square 
  centimeters 
  

   per 
  second. 
  With 
  this 
  datum 
  it 
  is 
  easy 
  to 
  compute 
  the 
  distri- 
  

   bution 
  of 
  the 
  diffusing 
  salt 
  at 
  any 
  time.* 
  The 
  following 
  table 
  

   is 
  computed 
  for 
  one 
  year 
  and 
  for 
  1000 
  years 
  from 
  the 
  com- 
  

   mencement 
  of 
  diffusion. 
  The 
  distances 
  are 
  measured 
  in 
  centi- 
  

   meters 
  from 
  the 
  contact, 
  and 
  under 
  " 
  saturation 
  " 
  the 
  quantity 
  

   of 
  sulphate 
  of 
  copper 
  per 
  unit 
  volume 
  of 
  the 
  substance 
  at 
  cor- 
  

   responding 
  distance 
  is 
  given, 
  the 
  strength 
  of 
  the 
  original 
  undif- 
  

   fused 
  sulphate 
  solution 
  being 
  taken 
  as 
  unity 
  : 
  

  

  Saturation. 
  

  

  

  Distance 
  

  

  in 
  centimeters 
  ; 
  

  

  time 
  1 
  year. 
  

  

  

  Distance 
  

   in 
  meters 
  ; 
  

   time 
  1000 
  years. 
  

  

  1-000 
  

  

  

  o- 
  

  

  

  0. 
  

  

  •750 
  

  

  

  3-96 
  cm 
  

  

  

  l-25 
  m 
  

  

  •500 
  

  

  

  8-36 
  

  

  

  2-77 
  

  

  •250 
  

  

  

  14-24 
  

  

  

  4-50 
  

  

  •100 
  

  

  

  20-37 
  

  

  

  6-44 
  

  

  •050 
  

  

  

  24-45 
  

  

  

  7-73 
  

  

  •025 
  

  

  

  27-76 
  

  

  

  8-78 
  

  

  •010 
  

  

  

  31-91 
  

  

  

  10-19 
  

  

  •005 
  

  

  

  35 
  04 
  

  

  

  11-08 
  

  

  Diffusion 
  of 
  CuS0 
  4 
  at 
  the 
  end 
  of 
  1 
  year 
  and 
  of 
  1000 
  years 
  [or 
  of 
  hypothetical 
  

   lava 
  at 
  the 
  end 
  of 
  50 
  times 
  these 
  periods; 
  or 
  of 
  heat 
  in 
  underground 
  strata 
  after 
  

   2 
  h 
  « 
  m 
  and 
  of 
  89 
  days]. 
  

  

  The 
  last 
  number 
  in 
  this 
  table 
  shows 
  only 
  half 
  of 
  1 
  per 
  cent 
  

   of 
  the 
  original 
  solution 
  and 
  this 
  may 
  be 
  taken 
  as 
  the 
  limit 
  of 
  

   sensible 
  diffusion. 
  It 
  is 
  easy 
  to 
  derive 
  from 
  this 
  table 
  the 
  

   figures 
  for 
  any 
  other 
  time. 
  Thus 
  after 
  a 
  hundred 
  years 
  the 
  

   distances 
  answering 
  to 
  the 
  given 
  saturations 
  will 
  be 
  ten 
  times 
  as 
  

   great 
  ; 
  sensible 
  diffusion 
  will 
  cease 
  at 
  350 
  cm 
  and 
  semi-saturation 
  

  

  * 
  For 
  the 
  necessary 
  Information 
  on 
  this 
  computation 
  see 
  Kelvin's 
  Math, 
  and 
  

   Phys. 
  Papers, 
  vol. 
  iii, 
  p. 
  432, 
  or 
  Brit. 
  Assoc. 
  Rep., 
  1888. 
  

  

  