﻿6 
  JOURNAL 
  OF 
  THE 
  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  VOL. 
  12, 
  NO. 
  1 
  

  

  allowable 
  strain 
  in 
  this 
  particular 
  case 
  was 
  given 
  as 
  A^ 
  = 
  20. 
  We 
  

   then 
  find 
  

  

  13 
  X 
  30^ 
  

   *' 
  = 
  0.075X0.725X20 
  '"'""'"' 
  = 
  ^°^''° 
  "'""^'^ 
  = 
  ^'^ 
  ^^^^- 
  

  

  13 
  X 
  30^ 
  

   Total 
  time 
  = 
  66.9 
  X 
  — 
  — 
  minutes 
  = 
  39140 
  minutes 
  = 
  27.2 
  days. 
  

  

  0.075 
  

   = 
  13 
  ^ 
  3Q2 
  = 
  0.0000064. 
  

  

  Therefore 
  ^o=419° 
  C. 
  (see 
  table 
  5 
  and 
  equation 
  (8), 
  op. 
  cit.), 
  and 
  

  

  30^ 
  

  

  ho 
  = 
  0.33 
  X 
  ^2 
  X 
  1440° 
  C. 
  per 
  day 
  = 
  2.11° 
  C. 
  per 
  day. 
  The 
  glass 
  

  

  should 
  therefore 
  be 
  held 
  at 
  419° 
  C. 
  for 
  seven 
  and 
  one-half 
  days 
  and 
  then 
  

   cooled, 
  the 
  initial 
  cooling 
  rate 
  being 
  a 
  little 
  over 
  2° 
  per 
  day 
  and 
  in- 
  

   creasing 
  as 
  in 
  the 
  table. 
  

  

  TABLE 
  1. 
  — 
  Schedule 
  According 
  to 
  Which 
  the 
  Cooling 
  Rate 
  Should 
  Be 
  Increased 
  

  

  Initial 
  rate 
  1.00 
  

  

  Rate 
  after 
  10° 
  cooling 
  1.12 
  

  

  Rate 
  after 
  20 
  ° 
  cool 
  ing 
  1 
  .36 
  

  

  Rate 
  after 
  30 
  "cooling 
  1.73 
  

  

  Rate 
  after 
  40° 
  cooling 
  2.30 
  

  

  Rate 
  after 
  50° 
  cooling 
  3.15 
  

  

  Rateafter 
  60° 
  cooling 
  4.36 
  

  

  Rate 
  after 
  70 
  ° 
  cooling 
  6.12 
  

  

  Rate 
  after 
  80° 
  cooling 
  8.60 
  

  

  Rateafter 
  90° 
  cooling 
  12.15 
  

  

  Rateafter 
  100° 
  cooling" 
  17.14 
  

  

  " 
  In 
  the 
  later 
  part 
  of 
  the 
  range 
  the 
  cooling-rate 
  practically 
  doubles 
  every 
  20 
  °. 
  

  

  SUMMARY 
  

  

  From 
  the 
  equations 
  representing 
  the 
  results 
  of 
  experimental 
  work 
  

   previously 
  described, 
  the 
  most 
  favorable 
  conditions 
  for 
  annealing 
  a 
  

   given 
  piece 
  of 
  glass 
  can 
  be 
  deduced. 
  Formulas 
  are 
  found 
  which, 
  

   used 
  in 
  conjunction 
  with 
  tables 
  of 
  the 
  elastic 
  and 
  annealing 
  constants 
  

   of 
  the 
  glass, 
  show 
  at 
  what 
  temperature 
  to 
  hold 
  the 
  glass, 
  how 
  long 
  

   to 
  hold 
  it 
  at 
  that 
  temperature, 
  and 
  how 
  rapidly 
  to 
  cool 
  it 
  in 
  order 
  to 
  

   get 
  any 
  degree 
  of 
  fineness 
  of 
  annealing 
  in 
  the 
  least 
  possible 
  time. 
  

   Examples 
  are 
  solved 
  to 
  illustrate 
  the 
  processes. 
  

  

  