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  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1929 
  

  

  mal 
  contact 
  with 
  materials 
  that 
  one 
  wishes 
  to 
  cool; 
  consequently, 
  it 
  

   is 
  frequently 
  mixed 
  with 
  alcohol 
  or 
  ether 
  to 
  overcome 
  this 
  disad- 
  

   vantage 
  of 
  poor 
  contact. 
  

  

  Within 
  the 
  last 
  few 
  years 
  methods 
  have 
  been 
  devised 
  to 
  use 
  this 
  

   carbon 
  dioxide 
  snow 
  industrially. 
  The 
  snow 
  as 
  formed 
  above 
  can 
  be 
  

   compressed 
  in 
  hydraulic 
  presses 
  so 
  as 
  to 
  form 
  a 
  dense, 
  hard 
  cake 
  with 
  

   a 
  specific 
  gravity 
  of 
  about 
  1.1 
  or 
  slightly 
  heavier 
  than 
  water. 
  This 
  

   dense 
  snow 
  or 
  "dry 
  ice, 
  " 
  as 
  it 
  is 
  called, 
  because 
  it 
  goes 
  directly 
  into 
  a 
  

   gas 
  from 
  the 
  solid, 
  is 
  being 
  used 
  to 
  a 
  considerable 
  extent 
  for 
  pacldng 
  

   ice 
  cream 
  or 
  frozen 
  fish 
  where 
  the 
  temperature 
  must 
  be 
  kept 
  consid- 
  

   erably 
  below 
  the 
  freezing 
  point. 
  One 
  large 
  manufacturer 
  of 
  ice 
  cream 
  

   in 
  Cambridge, 
  Mass., 
  is 
  shipping 
  75 
  per 
  cent 
  of 
  his 
  ice 
  cream 
  packed 
  

   in 
  carbon 
  dioxide 
  snow 
  rather 
  than 
  with 
  the 
  old 
  salt 
  and 
  ice 
  mixture. 
  

   One 
  gallon 
  of 
  ice 
  cream 
  is 
  placed 
  in 
  a 
  corrugated 
  cardboard 
  box 
  and 
  

   then 
  a 
  small 
  paper 
  bag 
  is 
  placed 
  on 
  top 
  containing 
  from 
  one 
  to 
  two 
  

   pounds 
  of 
  ''dry 
  ice," 
  depending 
  upon 
  the 
  atmospheric 
  temperature. 
  

   This 
  will 
  keep 
  the 
  ice 
  cream 
  in 
  excellent 
  condition 
  for 
  from 
  six 
  to 
  

   eight 
  hours, 
  and 
  there 
  are 
  many 
  obvious 
  advantages, 
  such 
  as 
  less 
  

   bulk 
  to 
  the 
  containers, 
  inexpensive 
  containers 
  that 
  can 
  be 
  discarded, 
  

   thus 
  saving 
  a 
  collection 
  trip, 
  and 
  no 
  wet 
  mixture 
  of 
  salt 
  and 
  ice 
  

   required. 
  

  

  Ice 
  cream 
  can 
  be 
  sliipped 
  long 
  distances 
  by 
  this 
  method 
  and 
  frozen 
  

   fish 
  have 
  remained 
  in 
  freight 
  cars 
  for 
  over 
  five 
  days 
  without 
  attention 
  

   when 
  packed 
  with 
  this 
  material. 
  It 
  has 
  been 
  recently 
  stated 
  that 
  in 
  

   shipping 
  ice 
  cream 
  from 
  Philadelphia 
  to 
  New 
  York 
  City, 
  200 
  pounds 
  

   of 
  "dry 
  ice 
  " 
  at 
  from 
  5 
  to 
  10 
  cents 
  per 
  pound 
  has 
  replaced 
  3,000 
  pounds 
  

   of 
  water 
  ice 
  and 
  GOO 
  pounds 
  of 
  salt. 
  In 
  this 
  case 
  3,400 
  pounds 
  of 
  extra 
  

   freight 
  is 
  avoided 
  besides 
  the 
  other 
  advantages. 
  Dry 
  ice 
  lasts 
  excep- 
  

   tionally 
  well 
  even 
  when 
  exposed 
  to 
  a 
  temperature 
  of 
  70° 
  F. 
  Recently 
  

   a 
  25-pound 
  cake 
  was 
  left 
  on 
  the 
  lecture 
  table 
  for 
  24 
  hours 
  exposed 
  to 
  

   room 
  temperature 
  and 
  even 
  after 
  that 
  period 
  of 
  time 
  2 
  or 
  3 
  pounds 
  

   were 
  still 
  left. 
  When 
  packed 
  in 
  insulated 
  contamers, 
  it 
  will, 
  of 
  

   course, 
  last 
  longer. 
  It 
  is 
  reported 
  that 
  a 
  New 
  York 
  apartment 
  house 
  

   is 
  using 
  it 
  in 
  all 
  its 
  refrigerators. 
  

  

  Another 
  recent 
  use 
  of 
  carbon 
  dioxide 
  snow 
  is 
  the 
  carbon 
  dioxide 
  

   snow 
  fire 
  extinguisher. 
  This 
  is 
  merely 
  a 
  tank 
  of 
  liquid 
  cat"bon 
  

   dioxide 
  under 
  pressure 
  with 
  a 
  hose 
  and 
  nozzle 
  connected 
  so 
  that 
  when 
  

   the 
  valve 
  is 
  opened, 
  carbon 
  dioxide 
  gas 
  and 
  snow 
  will 
  be 
  delivered 
  

   from 
  the 
  nozzle. 
  This 
  extinguisher 
  is 
  particularly 
  eft'ective 
  on 
  

   electrical 
  fires, 
  such 
  as 
  generators 
  or 
  telephone 
  switchboards, 
  because 
  

   it 
  will 
  not 
  conduct 
  electricity 
  and 
  does 
  not 
  injure 
  the 
  electrical 
  

   apparatus. 
  It 
  is 
  also 
  very 
  efi^ective 
  on 
  gasoline 
  or 
  oil 
  fires. 
  Since 
  

   the 
  gas 
  is 
  much 
  heavier 
  than 
  air, 
  the 
  fire 
  is 
  smothered 
  and 
  the 
  

   extremely 
  low 
  temperature 
  of 
  the 
  snow 
  cools 
  the 
  burning 
  material 
  

   below 
  the 
  ignition 
  temperature. 
  

  

  