﻿744 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Min. 
  per 
  Max. 
  per 
  Averas-p 
  

   cent 
  cent 
  Average 
  

  

  Moisture 
  .5 
  3.0 
  1.5 
  

  

  Silica 
  49.0 
  75.0 
  56.0 
  

  

  Alumina 
  11.0 
  26.0 
  22.5 
  

  

  Ferric 
  oxid 
  2.0 
  9.0 
  6.7 
  

  

  Lime 
  .* 
  .2 
  3.5 
  1.2 
  

  

  Magnesia 
  .1 
  3.0 
  1.4 
  

  

  Alkalis 
  1.0 
  5.5 
  3.7 
  

  

  Water 
  (loss 
  on 
  ign.) 
  3.0 
  13.0 
  7.0 
  

  

  Totalfluxes 
  13.0 
  

  

  In 
  addition 
  to 
  having 
  the 
  proper 
  chemical 
  composition, 
  it 
  should 
  

   also 
  possess 
  the 
  necessary 
  physical 
  properties. 
  

  

  Proper 
  plasticity 
  is 
  of 
  vital 
  importance, 
  but 
  its 
  excessive 
  develop- 
  

   ment 
  is 
  equally 
  injurious. 
  The 
  reason 
  plasticity 
  has 
  such 
  import- 
  

   ance 
  is 
  that 
  clay 
  when 
  molded 
  by 
  the 
  stiff 
  mud 
  process 
  is 
  very 
  apt 
  

   to 
  tear 
  when 
  issuing 
  from 
  the 
  die, 
  unless 
  of 
  proper 
  plasticity. 
  

   Excessive 
  plasticity 
  tends 
  to 
  produce 
  a 
  laminated 
  brick 
  when 
  auger 
  

   machines 
  are 
  used. 
  The 
  effect 
  of 
  these 
  laminations 
  will 
  be 
  seen 
  in 
  

   the 
  tests 
  given 
  below. 
  

  

  As 
  paving 
  brick, 
  unless 
  made 
  of 
  fire 
  clay, 
  should 
  be 
  burned 
  to 
  the 
  

   point 
  of 
  vitrification, 
  it 
  is 
  essential 
  that 
  in 
  clays 
  used 
  for 
  this 
  pur- 
  

   pose 
  the 
  points 
  of 
  viscosity 
  and 
  incipient 
  fusion 
  should 
  lie 
  well 
  

   apart, 
  not 
  less 
  than 
  250° 
  F. 
  and 
  preferably 
  400° 
  F^ 
  

  

  The 
  color 
  of 
  a 
  paving 
  brick 
  is 
  no 
  indication 
  of 
  its 
  quality. 
  

  

  The 
  clay 
  should 
  not 
  show 
  any 
  disposition 
  to 
  blister 
  as 
  the 
  point 
  

   of 
  vitrification 
  is 
  approached, 
  but 
  this 
  is 
  likely 
  to 
  occur 
  if 
  an 
  excess 
  

   of 
  iron 
  is 
  present. 
  

  

  In 
  order 
  to 
  demonstrate 
  somewhat 
  definitely 
  what 
  are 
  the 
  char- 
  

   acters 
  of 
  a 
  good 
  paving 
  brick 
  shale, 
  the 
  tests 
  of 
  a 
  sample 
  utilized 
  

   in 
  Illinois 
  for 
  the 
  manufacture 
  of 
  paving 
  blocks 
  is 
  given 
  herewith. 
  

  

  The 
  shale 
  is 
  rather 
  fine-grained, 
  and 
  breaks 
  up 
  quite 
  easily 
  in 
  

   grinding. 
  It 
  was 
  ground 
  to 
  pass 
  through 
  a 
  30 
  mesh 
  sieve. 
  28,*^ 
  of 
  

  

  ' 
  OlchewRky 
  in 
  Post. 
  chem. 
  tech. 
  anolyf<e. 
  18^0; 
  VVheelfr 
  in 
  Vitrified 
  

   paving 
  trick. 
  1895. 
  

  

  