﻿170 
  

  

  C. 
  Barus 
  — 
  Rot 
  Water 
  and 
  Soft 
  Glass 
  

  

  of 
  time. 
  Od 
  casual 
  inspection 
  one 
  might 
  ascribe 
  this 
  result 
  to 
  

   an 
  expansion 
  of 
  the 
  solidifying 
  core: 
  but 
  the 
  occurrence 
  of 
  the 
  

   bubbles 
  mentioned, 
  which 
  open 
  out 
  with 
  the 
  great 
  rapidity 
  

   attributable 
  only 
  to 
  solidification, 
  and 
  the 
  fact 
  that 
  breakage 
  

   (cf. 
  fig. 
  5, 
  h) 
  is 
  often 
  only 
  confined 
  to 
  the 
  water 
  glass 
  core 
  

   (being 
  a 
  longitudinal 
  fissure 
  within 
  this, 
  not 
  extending 
  to 
  the 
  

   igneous 
  glass 
  envelope), 
  show 
  that 
  an 
  intense 
  strain 
  of 
  dilata- 
  

  

  -jQm 
  jfifc 
  -ffim 
  ^Tu 
  JffiHi 
  7^ 
  

  

  tion 
  is 
  encountered. 
  All 
  observations 
  indicate 
  contraction 
  with 
  

   large 
  volume-coefficient, 
  too 
  large 
  for 
  the 
  igneous 
  glass 
  to 
  follow. 
  

   Some 
  rough 
  measurements 
  of 
  the 
  coefficient 
  of 
  expansion, 
  

   the 
  best 
  available 
  under 
  the 
  circumstances, 
  gave 
  between 
  25° 
  

   and 
  185° 
  a 
  coefficient 
  -0020. 
  The 
  mean 
  coefficient 
  of 
  water 
  

   within 
  these 
  limits 
  would 
  be 
  but 
  -0008. 
  Something 
  of 
  this 
  

   order 
  must 
  obtain 
  if 
  within 
  a 
  capillary 
  section 
  and 
  a 
  moderate 
  

   interval 
  of 
  temperature, 
  tensile 
  stresses 
  sufficient 
  to 
  rupture 
  the 
  

   tube 
  are 
  to 
  be 
  developed 
  on 
  cooling. 
  But 
  the 
  bubbles 
  and 
  

   stresses 
  thus 
  resemble 
  the 
  occurrences 
  which 
  in 
  Prince 
  Rupert 
  

   drops 
  require 
  so 
  much 
  higher 
  a 
  temperature 
  to 
  produce 
  them. 
  

   Special 
  mention 
  may 
  here 
  again 
  be 
  given 
  to 
  the 
  acceleration 
  

   of 
  the 
  rate 
  of 
  reaction 
  with 
  increasing 
  temperature. 
  At 
  185° 
  

   there 
  is 
  mainly 
  swelling 
  and 
  absorption. 
  At 
  210° 
  the 
  reaction 
  

  

  