﻿230 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  19 
  2 
  9 
  

  

  Primitive 
  man 
  found 
  that 
  an 
  over 
  supply 
  of 
  meat 
  from 
  a 
  success- 
  

   ful 
  hunt 
  could 
  be 
  preserved 
  for 
  a 
  longer 
  period 
  of 
  time 
  if 
  he 
  kept 
  it 
  

   in 
  an 
  underground 
  cavern, 
  a 
  well, 
  or 
  in 
  the 
  water 
  from 
  a 
  spring 
  or 
  

   other 
  relatively 
  cool 
  place. 
  In 
  a 
  temperate 
  climate 
  like 
  that 
  in 
  

   New 
  England, 
  the 
  temperature 
  of 
  the 
  air 
  may 
  vary 
  as 
  much 
  as 
  40° 
  in 
  

   a 
  day 
  and 
  as 
  much 
  as 
  100° 
  throughout 
  the 
  year. 
  The 
  daily 
  variation 
  

   affects 
  underground 
  temperatures 
  only 
  to 
  a 
  slight 
  extent 
  at 
  a 
  depth 
  

   of 
  2 
  or 
  3 
  feet, 
  while 
  the 
  annual 
  variation 
  is 
  lost 
  at 
  a 
  depth 
  of 
  25 
  to 
  

   50 
  feet. 
  There 
  the 
  temperature 
  remains 
  practically 
  constant 
  through- 
  

   out 
  the 
  year 
  and 
  usually 
  approximates 
  the 
  average 
  yearly 
  tempera- 
  

   ture 
  of 
  the 
  surface. 
  For 
  this 
  reason, 
  water 
  from 
  deep 
  wells 
  usually 
  

   has 
  a 
  temperature 
  that 
  is 
  the 
  same 
  throughout 
  the 
  year; 
  similarly, 
  

   spring 
  water 
  is 
  at 
  almost 
  constant 
  temperature 
  because 
  this 
  water 
  

   comes 
  from 
  a 
  considerable 
  depth 
  below 
  the 
  ground 
  surface. 
  Anyone 
  

   who 
  has 
  had 
  the 
  opportunity 
  to 
  visit 
  caves 
  in 
  different 
  seasons, 
  nearly 
  

   always 
  finds 
  them 
  warm 
  in 
  winter 
  and 
  cool 
  in 
  summer. 
  This 
  and 
  

   the 
  common 
  method 
  of 
  placing 
  water 
  pipes 
  a 
  few 
  feet 
  underground 
  

   to 
  prevent 
  freezing 
  in 
  cold 
  weather, 
  illustrate 
  the 
  fact 
  that 
  the 
  

   variation 
  in 
  air 
  temperature 
  soon 
  disappears 
  at 
  a 
  sufficient 
  depth 
  

   underground. 
  

  

  Nearly 
  everyone 
  is 
  familiar 
  with 
  the 
  use 
  of 
  ice 
  and 
  salt 
  to 
  produce 
  

   temperatures 
  low 
  enough 
  to 
  freeze 
  ice 
  cream. 
  If 
  ice 
  and 
  salt 
  are 
  

   mixed 
  in 
  proper 
  proportions, 
  it 
  is 
  not 
  difficult 
  to 
  produce 
  a 
  tempera- 
  

   ture 
  of 
  0° 
  F., 
  and 
  by 
  using 
  calcium 
  chloride 
  in 
  place 
  of 
  salt, 
  con- 
  

   siderably 
  lower 
  temperatures 
  may 
  be 
  attained. 
  There 
  are 
  many 
  

   other 
  substances 
  that 
  may 
  be 
  used 
  with 
  ice 
  to 
  produce 
  temperatures 
  

   below 
  the 
  freezing 
  point 
  of 
  water, 
  such 
  as 
  ammonium 
  nitrate, 
  alcohol, 
  

   hydrochloric 
  acid, 
  and 
  so 
  on. 
  The 
  use 
  of 
  niter 
  (potassium 
  nitrate) 
  

   with 
  snow 
  or 
  ice 
  has 
  long 
  been 
  known. 
  As 
  early 
  as 
  1550 
  it 
  is 
  said 
  

   the 
  Roman 
  nobles 
  cooled 
  their 
  wines 
  by 
  snow 
  and 
  niter. 
  

  

  In 
  temperate 
  climates, 
  ice 
  has 
  for 
  many 
  years 
  been 
  used 
  to 
  produce 
  

   low 
  temperatures. 
  Its 
  melting 
  point 
  is 
  32° 
  F. 
  which 
  represents 
  the 
  

   lowest 
  temperature 
  that 
  one 
  can 
  expect 
  to 
  reach 
  with 
  the 
  use 
  of 
  ice 
  

   alone, 
  but 
  the 
  ordinary 
  domestic 
  ice 
  box 
  is 
  more 
  frequently 
  in 
  the 
  

   neighborhood 
  of 
  50° 
  F. 
  as 
  a 
  recent 
  survey 
  of 
  a 
  large 
  number 
  of 
  

   refrigerators 
  determined. 
  Despite 
  the 
  enormous 
  sales 
  of 
  electrical 
  

   and 
  gas-heated 
  refrigerators 
  in 
  recent 
  years, 
  ice 
  will 
  continue 
  to 
  

   be 
  used, 
  probably 
  in 
  somewhat 
  lesser 
  quantities, 
  for 
  many 
  years 
  to 
  

   come, 
  because 
  of 
  the 
  low 
  cost 
  and 
  the 
  lack 
  of 
  many 
  minor 
  troubles 
  

   that 
  are 
  bound 
  to 
  arise 
  from 
  any 
  mechanical 
  unit. 
  

  

  The 
  cooling 
  effect 
  of 
  evaporation 
  has 
  been 
  utilized 
  for 
  centuries 
  

   by 
  the 
  peoples 
  living 
  in 
  hot, 
  dry 
  climates 
  who 
  store 
  their 
  drinking 
  

   water 
  in 
  porous 
  earthenware 
  jars. 
  Moisture 
  oozes 
  through 
  the 
  walls 
  

   to 
  the 
  outside 
  of 
  the 
  vessel 
  v/here 
  it 
  evaporates, 
  the 
  effect 
  of 
  which 
  is 
  

   sufficient 
  to 
  lower 
  the 
  temperature 
  of 
  the 
  water 
  from 
  10° 
  to 
  20° 
  

  

  