﻿376 
  new 
  york 
  State 
  museum 
  

  

  The 
  carbonic 
  acid 
  gas 
  passes 
  off 
  and 
  the 
  oxid 
  of 
  lime 
  remains 
  

   behind 
  as 
  a 
  white 
  powdery 
  or 
  lumpy 
  substance 
  but 
  may 
  be 
  more 
  

   or 
  less 
  colored 
  if 
  iron 
  is 
  present. 
  

  

  As 
  limestone 
  varies 
  in 
  composition 
  the 
  lime 
  will 
  also 
  but 
  the 
  

   percentage 
  of 
  impurities 
  in 
  the 
  lime 
  will 
  be 
  nearly 
  twice 
  what 
  

   they 
  were 
  in 
  the 
  limestone 
  for 
  the 
  latter 
  has 
  lost 
  46$ 
  of 
  carbonic 
  

   acid 
  gas. 
  

  

  Depending 
  on 
  the 
  amount 
  and 
  nature 
  of 
  the 
  impurities 
  present 
  

   we 
  may 
  divide 
  natural 
  and 
  artificial 
  limes 
  suitable 
  for 
  mortar 
  

   into 
  five 
  classes: 
  

  

  1 
  Common 
  or 
  fat 
  limes 
  

  

  2 
  Poor 
  or 
  meager 
  limes 
  /.'•"' 
  ' 
  

  

  3 
  Hydraulic 
  limes 
  ' 
  ' 
  ' 
  

  

  4 
  Hydraulic 
  cements 
  , 
  

  

  5 
  Natural 
  pozzuolanas 
  

  

  The 
  common 
  or 
  fat 
  limes 
  contain 
  less 
  than 
  10$ 
  impurities, 
  and 
  

   a 
  portion 
  of 
  the 
  latter 
  are 
  insoluble 
  in 
  water, 
  all 
  the 
  rest 
  of 
  the 
  

   lime 
  being 
  soluble. 
  They 
  do 
  not 
  harden 
  under 
  water 
  but 
  crum- 
  

   ble 
  or 
  slake 
  and 
  increase 
  in 
  volume 
  sometimes 
  threefold. 
  They 
  

   shrink 
  in 
  hardening 
  and 
  to 
  prevent 
  this 
  sand 
  must 
  be 
  added. 
  

  

  Poor 
  or 
  meager 
  limes 
  have 
  from 
  10 
  to 
  25$ 
  of 
  impurities 
  or 
  

   sometimes 
  even 
  39$. 
  

  

  Hydraulic 
  limes 
  are 
  of 
  three 
  kinds: 
  

  

  1 
  Slightly 
  hydraulic 
  ones 
  with 
  10 
  to 
  20$ 
  of 
  impurities. 
  

  

  2 
  Hydraulic 
  limes 
  with 
  17 
  to 
  24$ 
  impurities 
  

  

  3 
  Eminently 
  hydraulic 
  limes 
  with 
  20 
  to 
  35$ 
  of 
  impurities. 
  

  

  All 
  hydraulic 
  limes 
  harden 
  under 
  water. 
  Hydraulic 
  cement 
  is 
  

   an 
  artificial 
  product. 
  It 
  has 
  less 
  lime 
  than 
  the 
  other 
  classes/but 
  

   not 
  under 
  29$. 
  

  

  Natural 
  puzzuolanas 
  are 
  rocks 
  of 
  igneous 
  origin. 
  They 
  possess 
  

   hydraulicity 
  and 
  generally 
  contain 
  less 
  than 
  10$ 
  of 
  lime. 
  

  

  It 
  is 
  of 
  course 
  possible 
  to 
  find 
  all 
  intermediate 
  grades 
  between 
  

   limes 
  and 
  cements. 
  

  

  aGilmore. 
  On 
  limes, 
  hydraulic 
  cements 
  and 
  mortars, 
  p. 
  69. 
  

  

  