﻿284 
  G. 
  F. 
  Becker 
  — 
  Computing 
  Diffusion. 
  

  

  which 
  A 
  = 
  l//c, 
  or 
  in 
  the 
  case 
  of 
  salt 
  a 
  period 
  of 
  100,000 
  days, 
  

   while 
  the 
  values 
  for 
  7 
  correspond 
  for 
  salt 
  to 
  a 
  lapse 
  of 
  time 
  of 
  

   100,000 
  years. 
  

  

  In 
  connection 
  with 
  this 
  table 
  it 
  may 
  be 
  convenient 
  to 
  set 
  

   down 
  a 
  few 
  diffusivities 
  interesting 
  to 
  the 
  geologist, 
  either 
  

   immediately, 
  or 
  for 
  comparison 
  with 
  the 
  diffusivity 
  of 
  rock 
  

   magmas. 
  The 
  data 
  for 
  the 
  diffusion 
  of 
  heat 
  and 
  motion 
  are 
  

   taken 
  from 
  Lord 
  Kelvin's 
  memoir 
  on 
  Heat. 
  The 
  diffusivities 
  

   of 
  solutions 
  were 
  all 
  originally 
  published 
  in 
  terms 
  of 
  days, 
  not 
  

   seconds. 
  In 
  the 
  list 
  below 
  they 
  are 
  stated 
  both 
  in 
  this 
  way 
  

   under 
  \ 
  and 
  in 
  seconds 
  under 
  k. 
  In 
  choosing 
  illustrations 
  from 
  

   the 
  many 
  experiments 
  of 
  Scheffer 
  and 
  of 
  Schuhmeister'* 
  I 
  have 
  

   when 
  practicable 
  selected 
  two 
  nearly 
  at 
  the 
  same 
  temperature 
  

   with 
  different 
  concentrations, 
  and 
  a 
  third 
  at 
  a 
  different 
  tem- 
  

   perature 
  but 
  with 
  concentration 
  as 
  nearly 
  as 
  may 
  be 
  equal 
  to 
  

   that 
  of 
  one 
  or 
  other 
  of 
  the 
  first 
  two. 
  There 
  seems 
  no 
  doubt 
  

   that 
  k 
  in 
  the 
  case 
  of 
  liquids 
  varies 
  both 
  with 
  concentration 
  and 
  

   temperature. 
  The 
  variations 
  of 
  k, 
  however, 
  are 
  far 
  from 
  com- 
  

   plete 
  elucidation. 
  

  

  Mr. 
  Schuhmeister 
  remarks 
  that 
  "the 
  rapidity 
  of 
  diffusion 
  

   runs 
  almost 
  exactly 
  parallel 
  with 
  the 
  larger 
  or 
  smaller 
  values 
  

   of 
  the 
  coefficient 
  of 
  friction," 
  but 
  makes 
  no 
  further 
  comment 
  

   on 
  the 
  relations 
  of 
  viscosity 
  to 
  diffasivity. 
  In 
  an 
  investigation 
  

   undertaken 
  by 
  Mr. 
  A. 
  Sprungf 
  in 
  Prof. 
  Wiedemann's 
  labora- 
  

   tory, 
  for 
  the 
  purpose 
  of 
  determining 
  the 
  viscosity 
  of 
  salt 
  solu- 
  

   tions 
  over 
  wide 
  ranges 
  of 
  temperature 
  and 
  concentration, 
  

   diagrams 
  and 
  tables 
  are 
  given 
  which 
  enable 
  one 
  to 
  fix 
  the 
  

   viscosities 
  of 
  seven 
  salts 
  of 
  which 
  Mr. 
  Schuhmeister 
  has 
  deter- 
  

   mined 
  the 
  diffusivities 
  for 
  the 
  same 
  temperature 
  and 
  for 
  nearly 
  

   the 
  same 
  concentration. 
  Sprung's 
  concentrations 
  are 
  given 
  in 
  

   terms 
  of 
  the 
  weight 
  of 
  anhydrous 
  salt 
  per 
  100 
  parts 
  by 
  weight 
  

   of 
  solution. 
  Schuhmeister' 
  s 
  data 
  are 
  for 
  weight 
  of 
  anhydrous 
  

   salt 
  per 
  unit 
  volume 
  of 
  solution. 
  The 
  concentrations 
  being 
  

   1/10 
  and 
  the 
  temperature 
  10° 
  C, 
  k 
  the 
  diffusivity, 
  and 
  fx 
  the 
  

  

  coefficient 
  of 
  viscosity, 
  

  

  the 
  results 
  of 
  the 
  two 
  

  

  observers 
  are 
  

  

  expressed 
  in 
  the 
  first 
  three 
  lines 
  of 
  the 
  : 
  

  

  following 
  

  

  little 
  table. 
  

  

  Salt 
  KBr 
  KI 
  

  

  KC1 
  NaCl 
  

  

  CaCl 
  2 
  

  

  Na 
  2 
  S0 
  4 
  MgSO 
  4 
  

  

  kXIO 
  6 
  13-08 
  12-96 
  

  

  12-73 
  9-72 
  

  

  7-87 
  

  

  7-64 
  3-24 
  

  

  fi 
  0-126 
  0-124 
  

  

  0-128 
  0-156 
  

  

  0-169 
  

  

  0-179 
  0-247 
  

  

  k/x 
  2 
  X10 
  6 
  0-207 
  0-199 
  

  

  0-208 
  0-236 
  

  

  0-224 
  

  

  0244 
  0-198 
  

  

  *Mr. 
  J. 
  Schuhmeister's 
  investigation, 
  undertaken 
  at 
  Prof. 
  J. 
  Stefan's 
  adv'ce, 
  

   appeared 
  in 
  Wieu. 
  Sitz. 
  Ber. 
  Ak 
  Wiss.. 
  vol. 
  lxxix, 
  1879, 
  Part 
  IT, 
  p 
  603. 
  At 
  ihe 
  

   close 
  of 
  the 
  paper 
  mean 
  values 
  of 
  1 
  are 
  given 
  for 
  10° 
  C. 
  Stefan 
  recomputed 
  

   Graham's 
  diffusion 
  experiments. 
  His 
  paper 
  is 
  in 
  the 
  same 
  volume 
  as 
  Schuh- 
  

   meister's, 
  p. 
  161. 
  Mr. 
  J. 
  D. 
  R. 
  Scheffer's 
  memoir 
  on 
  diffusion 
  is 
  published 
  in 
  

   Verh. 
  Kon. 
  Ak. 
  van 
  Wet., 
  xxvi, 
  Part, 
  1888, 
  with 
  separate 
  pagination. 
  

  

  f 
  Pogg. 
  Ann 
  , 
  vol. 
  clix. 
  1876, 
  page 
  1. 
  

  

  