﻿538 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Whether 
  it 
  will 
  be 
  of 
  practical 
  advantage 
  to 
  carry 
  out 
  a 
  rational 
  

   analysis 
  to 
  this 
  extent 
  still 
  remains 
  to 
  be 
  seen. 
  In 
  its 
  simpler 
  form, 
  

   however, 
  when 
  applied 
  to 
  high 
  grade 
  clays, 
  the 
  rational 
  analysis 
  has 
  

   been 
  found 
  to 
  possess 
  great 
  practical 
  value, 
  owing 
  to 
  the 
  fact 
  that 
  if 
  

   two 
  clays 
  have 
  the 
  same 
  rational 
  composition 
  they 
  will, 
  other 
  things 
  

   being 
  equal, 
  behave 
  much 
  alike 
  when 
  burned. 
  This 
  fact 
  is 
  made 
  

   use 
  of 
  by 
  the 
  potter, 
  for 
  example, 
  in 
  the 
  preparation 
  of 
  his 
  porcelain 
  

   or 
  white 
  earthenware 
  mixture, 
  also 
  by 
  manufacturers 
  of 
  encaustic 
  

   tiles, 
  fire 
  brick, 
  etc. 
  

  

  To 
  illustrate 
  this 
  point 
  we 
  may 
  take 
  the 
  manufacture 
  of 
  porce- 
  

   lain. 
  Porcelain 
  is 
  made 
  from 
  a 
  mixture 
  of 
  kaolin, 
  quartz 
  and 
  

   feldspar. 
  Suppose 
  that 
  we 
  are 
  using 
  for 
  the 
  manufacture 
  of 
  porce- 
  

   lain 
  or 
  fire 
  brick 
  a 
  kaolin 
  which 
  has 
  67.82^ 
  of 
  clay 
  substance, 
  

   30.93 
  of 
  quartz, 
  and 
  1.25 
  of 
  feldspar, 
  and 
  that 
  to 
  100 
  parts 
  of 
  this 
  

   are 
  added 
  50 
  partfe 
  of 
  feldspar. 
  This 
  would 
  give 
  us 
  a 
  mixture 
  of 
  

   45.21^ 
  of 
  clay 
  substance, 
  20.62 
  of 
  quartz, 
  and 
  34.17 
  of 
  feldspar. 
  

  

  If 
  now 
  for 
  the 
  clay 
  we 
  had 
  been 
  using 
  we 
  substituted 
  one 
  with 
  

   66.33^ 
  of 
  clay 
  substance, 
  15.61 
  of 
  quartz, 
  and 
  18.91 
  of 
  feldspar, 
  

   and 
  made 
  no 
  other 
  changes, 
  the 
  mixture 
  would 
  then 
  contain 
  44.22;^ 
  

   of 
  clay 
  substance, 
  10.41 
  of 
  quartz, 
  and 
  45.98 
  of 
  feldspar. 
  

  

  This 
  last 
  mixture 
  shows 
  such 
  an 
  increase 
  in 
  feldspar 
  that 
  it 
  must 
  

   give 
  much 
  greater 
  shrinkage 
  and 
  fusibility; 
  but, 
  knowing 
  the 
  

   rational 
  analysis 
  of 
  the 
  new 
  clay, 
  it 
  would 
  be 
  easy, 
  by 
  making 
  a 
  

   simple 
  calculation, 
  to 
  ascertain 
  how 
  much 
  quartz 
  or 
  feldspar 
  should 
  

   be 
  added 
  to 
  bring 
  the 
  mixture 
  back 
  to 
  its 
  normal 
  composition. 
  

  

  Physical 
  properties 
  

  

  These 
  properties 
  are 
  fully 
  as 
  important 
  as 
  the 
  chemical, 
  if 
  not 
  

   more, 
  plasticity 
  for 
  instance 
  being 
  one 
  of 
  the 
  twO' 
  characters 
  in 
  

   clay 
  which 
  make 
  it 
  of 
  such 
  inestimable 
  value 
  to 
  man. 
  Similarity 
  

   in 
  chemical 
  composition 
  counts 
  for 
  little 
  in 
  the 
  comparison 
  of 
  two 
  

   clays, 
  if 
  they 
  do 
  not 
  agree 
  in 
  physical 
  characters. 
  

  

  The 
  physical 
  properties 
  of 
  the 
  most 
  importance 
  from 
  a 
  practical 
  

   standpoint 
  are 
  plasticity, 
  fusibility, 
  shrinkage, 
  tensile 
  strength, 
  

   slaking, 
  absorption 
  and 
  density. 
  

  

  