﻿390 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  are 
  now 
  classed 
  as 
  hydraulic 
  agents, 
  hydraulic 
  limes, 
  slag^ 
  

   cements, 
  natural 
  cements 
  and 
  portland 
  cements. 
  Hydraulio 
  

   agents 
  are 
  materials 
  which 
  cause 
  silica 
  and 
  clay 
  to 
  unite 
  

   with 
  the 
  lime 
  of 
  common 
  mortar, 
  giving 
  us 
  a 
  combination 
  

   of 
  slow 
  hardening. 
  Such 
  hydraulic 
  agents 
  may 
  be 
  natural 
  or 
  

   they 
  may 
  be 
  artificial. 
  The 
  natural 
  ones 
  are 
  represented 
  by 
  the 
  

   pozzuolana 
  of 
  Italy, 
  and 
  the 
  trass 
  of 
  the 
  Rhine 
  valley 
  in 
  Ger- 
  

   many. 
  In 
  this 
  country 
  they 
  are 
  only 
  known 
  in 
  the 
  far 
  west. 
  

   The 
  artificial 
  hydraulic 
  agents 
  include 
  slag, 
  burned 
  clay, 
  shales, 
  

   ashes, 
  silicate 
  of 
  soda 
  or 
  any 
  inorganic 
  material 
  that 
  contains 
  

   clay 
  and 
  silica 
  in 
  a 
  form 
  permitting 
  its 
  solution 
  in 
  acids. 
  

  

  Hydraulic 
  limes 
  

   Schoeh 
  divides 
  these 
  into 
  three 
  classes 
  : 
  

  

  True 
  hydraulic 
  limes. 
  These 
  contain 
  over 
  70$ 
  of 
  lime 
  carbon- 
  

   ate 
  

  

  2 
  Roman 
  cements, 
  with 
  50$ 
  to 
  70$ 
  of 
  lime 
  carbonates 
  

  

  3 
  Dolomitic 
  cements 
  or 
  magnesian 
  cements 
  

  

  1 
  Hydraulic 
  lime. 
  When 
  the 
  clayey 
  impurities 
  increase 
  in 
  ordi- 
  

   nary 
  quicklime, 
  it 
  assumes 
  hydraulic 
  properties 
  and 
  the 
  lime 
  is 
  

   known 
  as 
  hydraulic. 
  Sand 
  is 
  an 
  impurity 
  which 
  is 
  not 
  too 
  large 
  

   to 
  prevent 
  its 
  slaking 
  but 
  simply 
  retards 
  this 
  operation. 
  Hy- 
  

   draulic 
  limes 
  with 
  only 
  5 
  to 
  15$ 
  of 
  silicates 
  will 
  harden 
  in 
  from 
  

   8 
  to 
  20 
  days, 
  but 
  with 
  a 
  larger 
  amount 
  in 
  from 
  one 
  to 
  four 
  days. 
  

   No 
  sharp 
  line 
  can 
  be 
  drawn 
  between 
  pure 
  cements 
  and 
  hydraulic 
  

   limes. 
  

  

  True 
  hydraulic 
  limes 
  generally 
  have 
  18 
  to 
  25$ 
  of 
  clay, 
  free 
  

   silicia 
  and 
  combined 
  silica, 
  iron 
  oxid 
  and 
  alumina, 
  sometimes 
  

   magnesia 
  and 
  alkalies. 
  

  

  The 
  burning 
  of 
  hydraulic 
  lime 
  must 
  be 
  carried 
  on 
  very 
  slowly. 
  

   The 
  higher 
  the 
  percentage 
  of 
  total 
  silicates, 
  the 
  lower 
  must 
  be 
  

   the 
  temperature 
  of 
  burning 
  for 
  under 
  no 
  circumstances 
  should 
  

   the 
  material 
  be 
  allowed 
  to 
  sinter 
  as 
  it 
  does 
  in 
  the 
  case 
  of 
  portland 
  

   cement. 
  Such 
  overburned 
  pieces 
  slake 
  very 
  slowly. 
  Further- 
  

   more 
  the 
  burning 
  should 
  only 
  go 
  to 
  the 
  point 
  of 
  driving 
  off 
  the 
  

  

  