﻿112 
  Van 
  Name 
  and 
  Brown 
  — 
  Freezing 
  Point 
  Lowering. 
  

  

  glass 
  tubes 
  through 
  which 
  cold 
  brine* 
  is 
  circulated, 
  is 
  the 
  essen- 
  

   tial 
  feature 
  of 
  the 
  apparatus. 
  

  

  As 
  the 
  brine 
  enters 
  by 
  the 
  inner 
  tube 
  its 
  temperature 
  is 
  

   shown 
  bj 
  a 
  small 
  thermometer. 
  At 
  the 
  beginning 
  of 
  a 
  deter- 
  

   mination 
  the 
  inner 
  tube 
  is 
  drawn 
  up 
  slightly 
  so 
  that 
  there 
  is 
  a 
  

   free 
  passage 
  between 
  the 
  two 
  tubes 
  at 
  the 
  bottom. 
  The 
  brine 
  

   passes 
  down 
  the 
  inner 
  tube, 
  rises 
  between 
  the 
  inner 
  and 
  outer 
  

   tubes, 
  thus 
  exerting 
  its 
  cooling 
  effect 
  on 
  the 
  liquid 
  outside, 
  and 
  

   finally 
  escapes 
  through 
  the 
  side 
  tube. 
  When 
  the 
  desired 
  

   degree 
  of 
  undercooling 
  has 
  been 
  obtained, 
  the 
  inner 
  tube 
  is 
  

   lowered 
  until 
  in 
  close 
  contact 
  with 
  the 
  outer 
  tube 
  at 
  the 
  

   bottom, 
  where 
  it 
  has 
  been 
  ground 
  to 
  a 
  fit, 
  thus 
  stopping 
  the 
  

   circulation 
  through 
  the 
  lower 
  part 
  of 
  the 
  cooling 
  system. 
  This 
  

   is 
  the 
  position 
  shown 
  in 
  fig. 
  1. 
  The 
  lowering 
  of 
  the 
  inner 
  

   tube 
  uncovers 
  a 
  hole 
  in 
  that 
  tube, 
  previously 
  covered 
  by 
  the 
  

   rubber 
  stopper 
  E, 
  and 
  the 
  brine 
  now 
  circulates 
  only 
  through 
  

   the 
  upper 
  portion 
  of 
  the 
  cooling 
  tube 
  which 
  projects 
  from 
  the 
  

   apparatus. 
  80 
  long 
  as 
  the 
  inner 
  tube 
  is 
  in 
  this 
  lower 
  position 
  

   the 
  upper 
  part 
  of 
  the 
  cooling 
  device 
  is 
  thus 
  kept 
  at 
  a 
  tempera- 
  

   ture 
  below 
  that 
  of 
  the 
  solution, 
  and 
  by 
  an 
  amount 
  which 
  is 
  

   easily 
  regulated. 
  This 
  is 
  an 
  important 
  point 
  since 
  it 
  insures 
  

   that 
  such 
  transfer 
  of 
  heat 
  as 
  occurs 
  through 
  the 
  cooling 
  tube 
  

   shall 
  be 
  outward 
  rather 
  than 
  inward, 
  so 
  that 
  instead 
  of 
  pro- 
  

   moting 
  leakage 
  of 
  heat 
  into 
  the 
  apparatus, 
  as 
  it 
  might 
  otherwise 
  

   do, 
  the 
  cooling 
  device 
  actually 
  tends 
  to 
  compensate 
  for 
  such 
  

   leakage 
  as 
  occurs 
  elsewhere. 
  

  

  Fig. 
  2 
  shows 
  the 
  details 
  of 
  the 
  cooling 
  device, 
  though 
  with- 
  

   out 
  its 
  thermometer. 
  The 
  inner 
  tube 
  is 
  here 
  shown 
  raised, 
  in 
  

   the 
  position 
  for 
  undercooling. 
  All 
  the 
  upper 
  part 
  of 
  the 
  cool- 
  

   ing 
  tube, 
  down 
  to 
  a 
  point 
  below 
  the 
  level 
  of 
  the 
  liquid 
  into 
  

   which 
  it 
  dips, 
  is 
  surrounded 
  by 
  a 
  narrow 
  vacuum 
  jacket, 
  so 
  

   that 
  the 
  cooling 
  effect 
  is 
  exerted 
  only 
  below 
  the 
  surface 
  of 
  the 
  

   liquid. 
  This 
  prevents 
  accumulation 
  of 
  frost 
  on 
  the 
  cooling 
  

   tube 
  above 
  the 
  liquid, 
  which 
  would 
  be 
  apt 
  to 
  cause 
  premature 
  

   freezing, 
  and 
  therefore 
  permits 
  the 
  use 
  of 
  a 
  much 
  colder 
  brine, 
  

   making 
  the 
  whole 
  determination 
  a 
  great 
  deal 
  more 
  rapid. 
  An 
  

   unjacketed 
  cooling 
  tube 
  can 
  be 
  used 
  with 
  equally 
  accurate 
  

   results, 
  but 
  only 
  at 
  a 
  considerable 
  sacrifice 
  in 
  convenience. 
  

  

  The 
  brine 
  is 
  drawn 
  through 
  a 
  strainer 
  of 
  fine 
  wire 
  gauze 
  

   from 
  a 
  large 
  ice 
  and 
  salt 
  mixture 
  placed 
  slightly 
  above 
  tho 
  

   level 
  of 
  the 
  apparatus, 
  and 
  circulates 
  through 
  the 
  system 
  b}' 
  

   gravity, 
  the 
  rate 
  of 
  flow 
  being 
  regulated 
  by 
  screw 
  pinch-cocks 
  

   on 
  the 
  rubber 
  connecting 
  tubes. 
  It 
  is 
  collected 
  in 
  another 
  

  

  * 
  It 
  is 
  assumed 
  here 
  and 
  in 
  what 
  follows 
  that 
  we 
  are 
  dealing 
  with 
  the 
  meas- 
  

   urement 
  of 
  freezing 
  point 
  of 
  water 
  solutions, 
  since 
  this 
  is 
  by 
  far 
  the 
  common- 
  

   est 
  and 
  most 
  important 
  case, 
  and 
  is 
  the 
  one 
  to 
  which 
  our 
  practical 
  experience 
  

   with 
  the 
  apparatus 
  has 
  been 
  confined. 
  The 
  adaptability 
  of 
  the 
  method 
  for 
  

   other 
  solvents, 
  of 
  widely 
  differing 
  melting 
  points, 
  is, 
  however, 
  quite 
  obvious. 
  

  

  