﻿CLAYS 
  OF 
  NEW 
  YORK 
  569 
  

  

  In 
  the 
  third 
  group, 
  which 
  includes 
  the 
  brick 
  clays, 
  ' 
  the 
  alumina 
  

   percentage 
  is 
  small 
  as 
  compared 
  with 
  the 
  ferric 
  oxid. 
  They 
  are 
  

   all 
  easily 
  fused, 
  and 
  the 
  percentage 
  of 
  lime, 
  magnesia 
  and 
  alkalis 
  

   is 
  low 
  in 
  those 
  which 
  burn 
  to 
  a 
  bright 
  color. 
  The 
  usual 
  color 
  of 
  

   such 
  clays 
  when 
  burned 
  is 
  red, 
  which 
  becomes 
  deeper 
  with 
  an 
  in- 
  

   crease 
  in 
  the 
  temperature 
  and 
  gTeater 
  density, 
  changes 
  to 
  violet 
  

   red 
  and 
  finally 
  becomes 
  black. 
  

  

  The 
  percentage 
  of 
  ferric 
  oxid 
  is 
  generally 
  one 
  third 
  to 
  one 
  half 
  

   the 
  alumina 
  percentage, 
  as 
  indicated 
  by 
  the 
  following 
  figures 
  from 
  

   five 
  examples 
  given 
  by 
  Seger. 
  

  

  Color 
  when 
  burned 
  Dark 
  red 
  ^^^i^ferrid"" 
  ch£-ry\ed 
  ^ark 
  red 
  Dark 
  red 
  

  

  Eatio 
  of 
  AlaOg: 
  FeA 
  1:2.8 
  1:1. 
  19 
  i:i.9 
  1:1.29 
  1:1.29 
  

  

  A 
  comparison 
  of 
  the 
  second 
  and 
  third 
  groups 
  shows 
  that 
  those 
  

   in 
  which 
  the 
  alumina 
  is 
  not 
  more 
  than 
  three 
  times 
  as 
  great 
  as 
  

   the 
  ferric 
  oxid 
  show 
  a 
  decided 
  red 
  color 
  ; 
  those 
  where 
  it 
  is 
  five 
  and 
  

   one 
  half 
  times 
  as 
  great 
  show 
  a 
  brown 
  to 
  yellow 
  color. 
  

  

  Probably 
  other 
  physical 
  properties 
  exert 
  an 
  influence, 
  but 
  these 
  

   are 
  not 
  clearly 
  understood. 
  

  

  The 
  fourth 
  group 
  includes 
  calcareous 
  clays, 
  and 
  in 
  this 
  the 
  

   succession 
  of 
  colors 
  produced 
  in 
  burning 
  is 
  reversed. 
  The 
  ferric 
  

   oxid 
  exerts 
  its 
  coloring 
  action 
  at 
  low* 
  temperatures, 
  but 
  at 
  higher 
  

   ones 
  the 
  influence 
  of 
  the 
  lime 
  is 
  seen 
  en 
  tlie 
  silicates 
  of 
  the 
  clay, 
  

   and 
  the 
  red 
  passes 
  into 
  yellow 
  or 
  yellowish 
  white, 
  which 
  at 
  higher 
  

   temperatures 
  grades 
  into 
  green, 
  and 
  at 
  viscosity 
  becomes 
  dark 
  

   green 
  or 
  black. 
  

  

  The 
  relations 
  between 
  iron 
  and 
  alumina, 
  and 
  iron 
  and 
  lime, 
  

   and 
  the 
  color 
  when 
  burned 
  are 
  shown 
  below. 
  

  

  Color 
  With 
  light 
  burning 
  red 
  to 
  flesh 
  red 
  ; 
  hard 
  burning 
  yellow 
  white 
  to 
  

  

  sulphur 
  yellow; 
  at 
  vitrification 
  yellow 
  green 
  to 
  green 
  

  

  FeA: 
  AlA---- 
  1:2.3 
  1:1.16 
  1:3.1 
  1:2.5 
  1:2.5 
  1:2.4 
  

   Fe203:CaO 
  1:2.9 
  1:3.2 
  1:2.2 
  1:3.0 
  1:3.5 
  1:2.2 
  

  

  The 
  iron 
  in 
  this 
  group 
  runs 
  about 
  as 
  high 
  as 
  in 
  group 
  3, 
  the 
  

   lighter 
  color 
  being 
  due 
  to 
  lime, 
  the 
  percentage 
  of 
  which 
  ranges 
  

   from 
  11^-19^. 
  

  

  