﻿162 
  C. 
  Barus 
  — 
  Hot 
  Water 
  and 
  Soft 
  Glass 
  

  

  soft 
  glasses 
  than 
  with 
  infusible 
  hard 
  glasses. 
  In 
  all 
  cases, 
  

   of 
  course, 
  the 
  glass 
  must 
  be 
  quite 
  insoluble 
  in 
  water 
  under 
  

   ordinary 
  conditions 
  of 
  temperature. 
  In 
  the 
  present 
  experi- 
  

   ments 
  I 
  worked 
  with 
  the 
  common 
  glass 
  containing 
  lead, 
  of 
  the 
  

   kind 
  from 
  which 
  glass 
  rods 
  and 
  thick 
  tubes 
  are 
  usually 
  made, 
  

   and 
  I 
  was 
  further 
  induced 
  to 
  select 
  it 
  in 
  order 
  that 
  the 
  experi- 
  

   ments 
  on 
  a 
  larger 
  scale 
  might 
  be 
  made 
  with 
  the 
  identical 
  glass 
  

   of 
  my 
  capillary 
  tubes. 
  In 
  this 
  way 
  the 
  results 
  of 
  the 
  quantita- 
  

   tive 
  experiments 
  on 
  a 
  smaller 
  scale 
  in 
  glass 
  tubes 
  could 
  be 
  at 
  

   once 
  coordinated 
  with 
  the 
  experiments 
  in 
  steel 
  retorts. 
  

  

  2. 
  In 
  view 
  of 
  its 
  amorphous 
  structure 
  and 
  thermal 
  proper- 
  

   ties, 
  one 
  is 
  apt 
  to 
  look 
  upon 
  glass 
  as 
  colloidal, 
  and 
  it 
  is 
  expe- 
  

   dient 
  to 
  examine 
  at 
  the 
  outset 
  in 
  how 
  far 
  such 
  a 
  classification 
  

   is 
  tenable. 
  Glass 
  as 
  a 
  colloid 
  must 
  conform 
  to 
  the 
  general 
  

   relations 
  of 
  colloids 
  and 
  their 
  solvents, 
  and 
  one 
  must 
  be 
  able 
  

   to 
  predict 
  certain 
  peculiarities 
  in 
  the 
  behavior 
  of 
  glass 
  toward 
  

   water. 
  Colloids 
  (1) 
  at 
  favorable 
  temperatures 
  swell 
  up 
  enor- 
  

   mously 
  in 
  the 
  presence 
  of 
  their 
  solvents 
  ; 
  (2) 
  at 
  higher 
  tempera- 
  

   tures 
  the 
  swollen 
  coagulum 
  goes 
  over 
  into 
  clear 
  and 
  apparently 
  

   thorough 
  solution. 
  In 
  other 
  words, 
  the 
  coagulum 
  melts 
  in 
  its 
  

   menstruum, 
  mixes 
  with 
  it 
  completely 
  at 
  a 
  temperature 
  which 
  is 
  

   probably 
  characteristic 
  for 
  the 
  colloid 
  and, 
  so 
  far 
  as 
  known, 
  

   remarkably 
  independent 
  of 
  the 
  solvent 
  chosen. 
  

  

  It 
  is 
  essential, 
  however, 
  to 
  have 
  the 
  solvent 
  in 
  the 
  liquid 
  

   state. 
  These 
  conditions 
  are 
  at 
  once 
  fulfilled 
  for 
  the 
  case 
  of 
  

   starch, 
  of 
  gelatine 
  and 
  of 
  pure 
  rubber, 
  seeing 
  that 
  in 
  these 
  

   instances 
  the 
  dissolving 
  point 
  of 
  the 
  colloid 
  lies 
  below 
  the 
  

   boiling 
  point 
  of 
  the 
  solvent. 
  For 
  vulcanized 
  rubber 
  this 
  is, 
  as 
  

   a 
  rule, 
  not 
  the 
  case 
  ; 
  the 
  usual 
  solvents, 
  like 
  carbon 
  disulphide, 
  

   ether, 
  paraffine 
  oils, 
  chloroform, 
  etc., 
  boil 
  away 
  before 
  the 
  dis- 
  

   solving 
  point 
  (about 
  180°) 
  of 
  the 
  colloid 
  is 
  reached. 
  If, 
  how- 
  

   ever, 
  these 
  volatile 
  fluids 
  be 
  kept 
  liquid 
  under 
  pressure 
  up 
  to 
  

   185°, 
  vulcanized 
  rubber 
  passes 
  into 
  clear 
  solution 
  as 
  easily 
  as 
  

   starch. 
  Still 
  other 
  colloids, 
  like 
  wood, 
  decompose, 
  i. 
  e., 
  undergo 
  

   destructive 
  distillation 
  even 
  when 
  submerged 
  in 
  the 
  solvent 
  

   (water) 
  under 
  pressure, 
  below 
  the 
  dissolving 
  point. 
  

  

  I 
  shall 
  show 
  that 
  ordinary 
  glass 
  fulfills 
  the 
  above 
  conditions 
  

   perfectly 
  ; 
  but 
  before 
  doing 
  so 
  a 
  brief 
  description 
  of 
  the 
  experi- 
  

   ments 
  with 
  retorts 
  is 
  advisable. 
  

  

  3. 
  If 
  water 
  be 
  selected 
  as 
  a 
  suitable 
  colloidal 
  solvent 
  of 
  

   glass, 
  the 
  dissolving 
  point 
  will 
  certainly 
  lie 
  above 
  the 
  boiling 
  

   point 
  of 
  the 
  liquid. 
  Hence 
  it 
  is 
  necessary 
  to 
  make 
  use 
  of 
  high 
  

   pressure 
  retorts; 
  and 
  I 
  shall 
  take 
  the 
  liberty 
  of 
  describing 
  a 
  

   simple 
  and 
  efficient 
  form 
  which 
  has 
  served 
  me 
  not 
  only 
  in 
  the 
  

   present 
  but 
  in 
  many 
  similar 
  experiments. 
  

  

  ■ 
  In 
  the 
  figure 
  (1) 
  AB 
  is 
  a 
  piece 
  of 
  seamless 
  drawn 
  steel 
  tub- 
  

   ing 
  obtained 
  from 
  John 
  S. 
  Leng, 
  New 
  York, 
  about 
  45 
  cm 
  long 
  

  

  