﻿CLAYS 
  OF 
  TvEW 
  YORK 
  513 
  

  

  Ammonia. 
  Olajs 
  possess 
  a 
  strong 
  absorptive 
  capacity 
  for 
  gases 
  

   and 
  in 
  consequence 
  of 
  this 
  frequently 
  contain 
  an 
  appreciable 
  

   amount 
  of 
  ammonia, 
  to 
  which 
  is 
  largely 
  attributable 
  the 
  character- 
  

   istic 
  odor 
  of 
  clay.^ 
  

  

  While 
  the 
  presence 
  of 
  this 
  compound 
  may 
  exert 
  some 
  action 
  on 
  

   the 
  plasticity 
  and 
  absorptive 
  power 
  of 
  tlie 
  clay, 
  still 
  it 
  need 
  not 
  be 
  

   considered 
  in 
  burning, 
  for 
  it 
  passes 
  off 
  as 
  a 
  vapor 
  at 
  a 
  temperature 
  

   considerably 
  below 
  dull 
  redness, 
  or 
  may 
  even 
  volatilize 
  with 
  the 
  

   moisture 
  of 
  the 
  clay 
  during 
  the 
  early 
  stages 
  of 
  burning. 
  

  

  Fixed 
  alkalis. 
  These 
  include 
  potash, 
  soda 
  and 
  lithia, 
  but 
  the 
  

   latter 
  is 
  such 
  a 
  rare 
  constituent 
  that 
  it 
  need 
  not 
  be 
  considered. 
  

   Potash 
  and 
  soda 
  are 
  present 
  in 
  nearly 
  every 
  clay, 
  in 
  amounts 
  vary- 
  

   ing 
  from 
  a 
  mere 
  trace 
  to 
  10 
  fc^ 
  but 
  the 
  usual 
  average 
  is 
  1^-3^. 
  The 
  

   chief 
  sources 
  of 
  potash 
  and 
  soda 
  are 
  the 
  different 
  species 
  of 
  feld- 
  

   spar; 
  white 
  mica 
  or 
  muscovite 
  may 
  furnish 
  potash. 
  The 
  variation 
  

   in 
  amount 
  might 
  be 
  accounted 
  for 
  by 
  the 
  presence 
  of 
  undecomposed 
  

   feldspar 
  in 
  the 
  clay, 
  the 
  common 
  feldspar 
  orthoclase 
  containing 
  17^ 
  

   of 
  potash 
  alone. 
  

  

  AVlien 
  either 
  feldspar 
  or 
  mica 
  decomposes, 
  the 
  alkalis 
  are 
  con- 
  

   verted 
  wholly 
  or 
  in 
  part 
  into 
  soluble 
  compounds, 
  and 
  thus 
  w^e 
  get 
  

   both 
  soluble 
  and 
  insoluble 
  alkaline 
  compounds. 
  

  

  Soluble 
  alkaline 
  compounds. 
  These 
  may 
  be 
  present 
  in 
  any 
  clay, 
  

   but 
  they 
  seldom 
  occur 
  in 
  large 
  quantities. 
  They 
  may 
  influence 
  the 
  

   plasticity 
  of 
  the 
  clay, 
  by 
  causing 
  a 
  flocculation 
  of 
  the 
  particles; 
  but 
  

   their 
  chief 
  importance, 
  or 
  disadvantage, 
  is 
  in 
  giving 
  rise 
  to 
  the 
  

   formation 
  of 
  efflorescence 
  on 
  the 
  surface 
  of 
  the 
  ware, 
  where 
  they 
  

   become 
  concentrated 
  by 
  the 
  evaporation 
  of 
  the 
  moisture 
  in 
  the 
  clay, 
  

   unless 
  previously 
  rendered 
  insoluble 
  by 
  the 
  addition 
  of 
  proper 
  

   chemicals. 
  This 
  crust 
  may 
  interfere 
  vdth 
  the 
  formation 
  of 
  salt 
  

   glaze, 
  or 
  the 
  adhesion 
  of 
  a 
  glaze 
  applied 
  to 
  the 
  ware 
  before 
  burning. 
  

  

  Soluble 
  alkaline 
  sulfates 
  are 
  powerful 
  fluxes. 
  They 
  cause 
  

   blistering 
  of 
  the 
  ware 
  if 
  the 
  clay 
  is 
  heated 
  sufficiently 
  high 
  to 
  de- 
  

   compose 
  the 
  sulfate 
  and 
  permit 
  the 
  escape 
  of 
  sulfuric 
  acid 
  gas. 
  

  

  [ 
  ^ 
  F. 
  Senft. 
  Die 
  Thonsubstanzen 
  p. 
  29. 
  

  

  