﻿LIMESTONES 
  OF 
  NEW 
  YORK 
  AND 
  THEIR 
  ECONOMIC 
  VALUE 
  371 
  

  

  Composition 
  of 
  limestone 
  

  

  calcitic 
  and 
  consists 
  of 
  56$ 
  of 
  oxid 
  of 
  lime 
  and 
  44$ 
  carbonic 
  

   calcite 
  and 
  consists 
  of 
  56$ 
  of 
  oxid 
  of 
  lime 
  and 
  44$ 
  carbonic 
  

   acid. 
  It 
  rarely 
  occurs 
  perfectly 
  pure 
  as 
  the 
  impurities 
  seldom 
  

   get 
  below 
  1$; 
  they 
  may 
  also 
  increase 
  to 
  such 
  an 
  extent 
  as 
  to 
  

   prohibit 
  calling 
  the 
  rock 
  a 
  limestone. 
  The 
  impurities 
  commonly 
  

   present 
  are 
  silica, 
  alumina, 
  iron, 
  magnesia 
  and 
  organic 
  matter. 
  

   Traces 
  of 
  sulfuric 
  and 
  phosphoric 
  acid 
  are 
  also 
  met 
  with. 
  

  

  The 
  silica 
  may 
  be 
  present 
  as 
  pure 
  quartz 
  or 
  combined 
  with 
  

   the 
  alumina 
  in 
  the 
  form 
  of 
  clay, 
  and 
  less 
  frequently 
  as 
  an 
  ele- 
  

   ment 
  of 
  silicate 
  minerals 
  such 
  as 
  mica, 
  hornblende 
  or 
  pyroxene. 
  

  

  It 
  may 
  practically 
  be 
  looked 
  on 
  as 
  an 
  inert 
  impurity 
  dis- 
  

   placing 
  so 
  much 
  carbonate 
  of 
  lime. 
  At 
  high 
  temperatures 
  how- 
  

   ever 
  when 
  the 
  carbonic 
  acid 
  has 
  been 
  driven 
  off 
  and 
  oxid 
  of 
  

   lime 
  left, 
  the 
  silica 
  will 
  flux 
  this 
  lime 
  with 
  great 
  eagerness. 
  

   Alumina 
  is 
  usually 
  present 
  as 
  clay. 
  With 
  an 
  increase 
  in 
  the 
  per- 
  

   centage 
  of 
  the 
  latter 
  limestone 
  passes 
  into 
  cement 
  rock. 
  If 
  

   present 
  to 
  the 
  extent 
  of 
  4$ 
  or 
  5$ 
  alumina 
  is 
  an 
  inert 
  im- 
  

   purity 
  like 
  silica, 
  but 
  when 
  present 
  in 
  larger 
  amounts 
  it 
  facili- 
  

   tates 
  the 
  expulsion 
  of 
  the 
  carbonic 
  acid 
  gas. 
  The 
  reason 
  for 
  

   this 
  is 
  that 
  clay 
  contains 
  chemically 
  combined 
  water 
  which 
  only 
  

   passes 
  off 
  at 
  a 
  red 
  heat 
  or 
  at 
  the 
  same 
  time 
  as 
  the 
  carbonic 
  acid 
  

   gas. 
  This 
  provides 
  an 
  atmosphere 
  of 
  watery 
  vapor 
  into 
  which 
  

   the 
  carbonic 
  acid 
  gas 
  escapes 
  quicker 
  than 
  it 
  would 
  if 
  passing 
  

   off 
  into 
  gas 
  of 
  its 
  own 
  kind. 
  

  

  Iron 
  and 
  alkalies 
  if 
  present 
  in 
  appreciable 
  quantity 
  render 
  the 
  

   limestone 
  more 
  easily 
  fusible, 
  and 
  may 
  necessitate 
  the 
  handpick- 
  

   ing 
  of 
  the 
  burned 
  rock 
  to'separate 
  clinkers. 
  

  

  Magnesian 
  limestones 
  are 
  known 
  as 
  dolomites 
  when 
  the 
  per- 
  

   centage 
  of 
  magnesia 
  is 
  20 
  or 
  over. 
  The 
  rock 
  may 
  have 
  special 
  

   uses, 
  but 
  when 
  in 
  smaller 
  amounts 
  as 
  2 
  to 
  12$ 
  it 
  is 
  to 
  be 
  looked 
  

   on 
  as 
  displacing 
  equal 
  quantities 
  of 
  carbonate 
  of 
  lime 
  and 
  for 
  

   certain 
  purposes 
  as 
  a 
  deleterious 
  impurity. 
  

  

  Organic 
  matter 
  is 
  rarely 
  absent 
  in 
  limestones 
  and 
  a 
  very 
  small 
  

   amount 
  may 
  impart 
  a 
  gray 
  or 
  even 
  black 
  color 
  to 
  the 
  rock. 
  

  

  