﻿Becker 
  — 
  Some 
  Queries 
  on 
  Rock 
  Differentiation. 
  27 
  

  

  A. 
  A. 
  Noyes.* 
  Thus 
  the 
  solubility 
  of 
  lead 
  chloride 
  is 
  reduced 
  

   by 
  the 
  presence 
  of 
  other 
  chlorides 
  to 
  something 
  like 
  one-half 
  

   of 
  its 
  separate 
  solubility. 
  It 
  appears 
  substantially 
  certain 
  

   therefore 
  that 
  a 
  series 
  of 
  silicates 
  in 
  solution 
  must 
  restrict 
  the 
  

   solubility 
  of 
  each. 
  Consequently 
  conclusions 
  drawn 
  from 
  the 
  

   assumption 
  that 
  Fick's 
  hypothesis 
  is 
  exact 
  will 
  be 
  applicable 
  to 
  

   the 
  process 
  of 
  differentiation. 
  

  

  It 
  is 
  interesting 
  and 
  extremely 
  important 
  to 
  observe 
  that 
  the 
  

   problem 
  of 
  determining 
  the 
  distribution 
  of 
  a 
  diffusing 
  lava 
  is 
  

   formally 
  the 
  same 
  as 
  that 
  of 
  finding 
  the 
  distribution 
  of 
  tem- 
  

   perature 
  in 
  a 
  cooling 
  globe 
  of 
  large 
  radius. 
  This 
  last 
  is 
  a 
  sub- 
  

   ject 
  which 
  has 
  become 
  familiar 
  to 
  geologists 
  through 
  Lord 
  

   Kelvin's 
  application 
  of 
  the 
  results 
  in 
  estimating 
  the 
  age 
  of 
  the 
  

   earth. 
  

  

  The 
  diffusivity 
  of 
  a 
  substance 
  is 
  inversely 
  proportional 
  to 
  

   the 
  molecular 
  friction 
  which 
  the 
  molecules 
  or 
  the 
  ions 
  experi- 
  

   ence. 
  Thus 
  if 
  7\ 
  and 
  r 
  2 
  are 
  the 
  frictional 
  resistances 
  of 
  the 
  

   ions 
  of 
  an 
  electrolyte, 
  O 
  the 
  osmotic 
  pressure 
  and 
  D 
  the 
  dif- 
  

   fusivity, 
  then, 
  as 
  was 
  shown 
  by 
  Nernst 
  : 
  

  

  This 
  internal 
  friction 
  is 
  usually 
  known 
  in 
  English 
  as 
  vis- 
  

   cosity. 
  The 
  viscosity 
  of 
  liquids 
  so 
  far 
  as 
  is 
  known 
  increases 
  

   with 
  the 
  pressure 
  to 
  which 
  they 
  are 
  subjected, 
  with 
  the 
  excep- 
  

   tion 
  of 
  water, 
  which 
  at 
  ordinary 
  temperatures 
  becomes 
  less 
  

   viscous 
  with 
  increasing 
  pressure. 
  Of 
  course 
  water 
  at 
  tempera- 
  

   tures 
  approaching 
  its 
  freezing 
  point 
  is 
  an 
  anomalous 
  liquid. 
  

   According 
  to 
  Amagat, 
  the 
  anomalous 
  expansion 
  of 
  water 
  ceases 
  

   at 
  50° 
  C. 
  and 
  Tammann 
  suggests 
  that 
  the 
  exceptional 
  relation 
  

   between 
  viscosity 
  and 
  pressure 
  is 
  probably 
  confined 
  to 
  the 
  

   same 
  limit. 
  

  

  Rate 
  of 
  diffusion. 
  — 
  If 
  two 
  miscible 
  solutions 
  are 
  brought 
  in 
  

   contact 
  and 
  a 
  time 
  t, 
  measured 
  in 
  seconds, 
  is 
  allowed 
  to 
  elapse, 
  

   the 
  fluid 
  at 
  a 
  distance 
  of 
  x 
  centimeters 
  from 
  the 
  contact 
  will 
  

   contain 
  a 
  certain 
  amount 
  of 
  the 
  diffusing 
  fluid 
  per 
  cubic 
  centi- 
  

   meter, 
  which 
  may 
  be 
  called 
  s. 
  One 
  of 
  the 
  fluids 
  may 
  be 
  sup- 
  

   posed 
  kept 
  at 
  constant 
  composition, 
  as 
  in 
  the 
  case 
  of 
  a 
  solid 
  

   dissolving 
  in 
  a 
  solvent. 
  Then 
  this 
  same 
  concentration 
  s 
  will 
  

   be 
  found 
  at 
  nx 
  centimeters 
  after 
  the 
  lapse 
  of 
  tft 
  seconds. 
  For 
  

   example, 
  if 
  common 
  salt 
  is 
  brought 
  in 
  contact 
  with 
  water, 
  the 
  

   water 
  in 
  immediate 
  contact 
  with 
  the 
  salt 
  will 
  soon 
  become 
  

   saturated. 
  At 
  the 
  distance 
  of 
  l 
  cm 
  the 
  solution 
  will 
  be 
  half 
  satu- 
  

   rated 
  in 
  about 
  one 
  day 
  ; 
  at 
  2 
  cm 
  it 
  will 
  be 
  semi-saturated 
  in 
  four 
  

   days 
  and 
  at 
  100 
  cm 
  in 
  100 
  2 
  = 
  10,000 
  days 
  ; 
  at 
  100 
  meters 
  the 
  

  

  * 
  Zeitsch. 
  phys. 
  Chemie, 
  vol. 
  ix, 
  1892, 
  p. 
  623. 
  

  

  