﻿168 
  C. 
  Barns 
  — 
  Hot 
  Water 
  and 
  Soft 
  Glass 
  

  

  becomes 
  clear, 
  the 
  mercury 
  meniscus 
  glistens 
  brilliantly, 
  the 
  

   thread 
  breaks 
  into 
  shining 
  globules. 
  The 
  white 
  coagulum 
  

   clarifies 
  from 
  the 
  periphery 
  inward 
  toward 
  the 
  axis 
  of 
  the 
  tube, 
  

   where 
  it 
  gradually 
  vanishes. 
  Compressibility 
  at 
  first 
  increas- 
  

   ing 
  with 
  great 
  rapidity 
  to 
  an 
  enormous 
  value, 
  falls 
  off, 
  as 
  it 
  

   were, 
  suddenly 
  to 
  the 
  relatively 
  low 
  value 
  attributable 
  to 
  hot 
  

   water. 
  While 
  the 
  reaction 
  proceeds 
  the 
  solution 
  is 
  inelastic, 
  

   i. 
  e., 
  the 
  liquid 
  fails 
  to 
  expand 
  on 
  removal 
  of 
  pressure. 
  Vol- 
  

   ume 
  decrement 
  is 
  at 
  first 
  extremely 
  rapid, 
  finally 
  to 
  vanish 
  

   asymptotically 
  in 
  the 
  lapse 
  of 
  time. 
  The 
  tube 
  seen 
  through 
  

   the 
  telescope 
  shows 
  an 
  internal 
  current 
  continually 
  flowing 
  

   from 
  the 
  bottom 
  to 
  the 
  top, 
  and 
  this 
  current 
  persists 
  until 
  the 
  

   reaction 
  terminates 
  in 
  clearness 
  of 
  tube 
  and 
  saturated 
  water 
  

   glass. 
  The 
  effect 
  of 
  pressure 
  here 
  is 
  thus 
  virtually 
  an 
  accele- 
  

   ration 
  of 
  the 
  velocity 
  of 
  the 
  current, 
  and 
  hence 
  compressibility 
  

   may 
  be 
  rated 
  at 
  any 
  large 
  value 
  whatever, 
  since 
  the 
  additional 
  

   velocity 
  imparted 
  by 
  pressure 
  is 
  now 
  dependent 
  on 
  the 
  vis- 
  

   cosity 
  of 
  the 
  flowing 
  liquid. 
  For 
  this 
  reason, 
  moreover, 
  

   removal 
  of 
  pressure 
  produces 
  breakage 
  of 
  thread 
  and 
  cavities 
  

   in 
  the 
  viscous 
  silicate, 
  which 
  in 
  their 
  turn 
  swim 
  along 
  in 
  the 
  

   upgoing 
  current. 
  Cavities 
  and 
  mercury 
  globules 
  retain 
  their 
  

   relative 
  positions 
  to 
  each 
  other 
  during 
  the 
  motion, 
  though 
  the 
  

   former 
  may 
  often 
  be 
  brought 
  to 
  vanish 
  by 
  excess 
  of 
  pressure. 
  

   I 
  have 
  inferred 
  from 
  this 
  that 
  the 
  column 
  of 
  water 
  glass, 
  now 
  

   two 
  to 
  three 
  times 
  the 
  original 
  diameter 
  of 
  the 
  capillary 
  thread 
  

   of 
  water, 
  moves 
  as 
  a 
  whole 
  and 
  not 
  telescopically 
  at 
  a 
  decreas- 
  

   ing 
  rate 
  from 
  the 
  axis 
  outward 
  : 
  the 
  latter 
  case 
  would 
  imply 
  a 
  

   deformation 
  of 
  the 
  mercury 
  globules 
  which 
  has 
  not 
  been 
  

   observed. 
  The 
  mercury 
  threads 
  approximately 
  retain 
  their 
  

   original 
  diameter. 
  

  

  7. 
  To 
  obtain 
  a 
  clear 
  view 
  of 
  the 
  progress 
  of 
  the 
  reactions 
  

   here 
  in 
  question, 
  the 
  annexed 
  chart 
  of 
  a 
  typical 
  case 
  may 
  be 
  

   consulted, 
  in 
  which 
  volumes 
  (thread 
  lengths 
  in 
  cms.) 
  and 
  com- 
  

   pressibilities 
  are 
  laid 
  off 
  vertically, 
  and 
  the 
  corresponding 
  time 
  

   of 
  exposure 
  dated 
  from 
  the 
  beginning 
  of 
  heating, 
  horizontally. 
  

   It 
  will 
  be 
  seen 
  that 
  20 
  minutes 
  after 
  beginning 
  the 
  boiling 
  (less 
  

   than 
  10 
  minutes 
  of 
  exposure 
  to 
  210°) 
  the 
  hot 
  thread 
  has 
  con- 
  

   tracted 
  to 
  the 
  length 
  of 
  the 
  original 
  cold 
  thread, 
  and 
  that 
  con- 
  

   traction 
  proceeds 
  enormously 
  beyond 
  this. 
  The 
  total 
  volume 
  

   contraction 
  of 
  the 
  system 
  water 
  and 
  glass, 
  as 
  taken 
  from 
  the 
  

   chart, 
  would 
  be 
  over 
  30 
  per 
  cent 
  of 
  the 
  cold 
  length. 
  The 
  

   observed 
  changes 
  of 
  compressibility 
  would 
  be 
  from 
  about 
  

   100/10 
  6 
  per 
  atm., 
  for 
  nearly 
  pure 
  water, 
  to 
  something 
  like 
  

   600/10 
  6 
  for 
  dissolving 
  water 
  glass. 
  The 
  diameter 
  of 
  the 
  capil- 
  

   lary 
  increased 
  from 
  '024: 
  cm 
  (water), 
  to 
  -071 
  ctn 
  (water 
  glass), 
  

   upwards 
  three 
  times. 
  These 
  data 
  were 
  found 
  from 
  measure- 
  

   ments 
  made 
  on 
  sections 
  of 
  the 
  cold 
  tubes. 
  Cf. 
  fig. 
  5. 
  

  

  