﻿512 
  NEW 
  YOEK 
  STATE 
  MUSEUM 
  

  

  compounds 
  or 
  mineral 
  species, 
  wliieli 
  eitlier 
  already 
  exist 
  in 
  the 
  

   clay 
  or 
  may 
  be 
  added 
  to 
  it 
  artificially. 
  The 
  influence 
  of 
  fluxes 
  in- 
  

   creases 
  not 
  only 
  with 
  the 
  amount 
  present 
  but 
  also 
  with 
  the 
  state 
  

   of 
  division, 
  they 
  being 
  the 
  more 
  active 
  the 
  more 
  finely 
  they 
  are 
  

   divided. 
  If 
  the 
  flux 
  is 
  present 
  in 
  the 
  form 
  of 
  large 
  grains^ 
  

   these 
  grains 
  will 
  only 
  exert 
  a 
  fluxing 
  action 
  on 
  their 
  surface, 
  

   whereas 
  the 
  single 
  gi-ains 
  alone 
  will 
  act 
  more 
  like 
  quartz 
  grains, 
  

   that 
  is, 
  as 
  diluents 
  of 
  the 
  shrinkage. 
  The 
  minerals 
  which 
  may 
  

   be 
  present 
  as 
  fluxes 
  or 
  may 
  sometimes 
  be 
  added 
  are 
  mica, 
  feld- 
  

   spar, 
  and 
  similar 
  silicates, 
  slags, 
  lime 
  carbonate, 
  magnesia 
  car- 
  

   bonate, 
  and 
  various 
  compounds 
  of 
  iron 
  and 
  manganese. 
  In 
  addi- 
  

   tion 
  they 
  may 
  be 
  present 
  as 
  soluble 
  salts. 
  It 
  i» 
  usually 
  the 
  oxids 
  

   of 
  iron, 
  manganese, 
  and 
  complex 
  silicates 
  containing 
  these 
  as 
  well 
  

   as 
  lime, 
  magnesium, 
  potash, 
  and 
  soda 
  that 
  determine 
  the 
  degree 
  of 
  

   fusibility 
  of 
  the 
  clay. 
  

  

  The 
  amount 
  of 
  fluxes 
  which 
  a 
  clay 
  contains 
  has 
  an 
  important 
  

   bearing 
  on 
  its 
  applicability. 
  For 
  some 
  purposes 
  it 
  is 
  desirable 
  as 
  

   well 
  as 
  necessary 
  that 
  the 
  percentage 
  of 
  fluxes 
  should 
  be 
  low 
  

   (producing 
  refractory 
  wares), 
  not 
  only 
  with 
  a 
  view 
  to 
  refractoriness, 
  

   but 
  also, 
  as 
  in 
  porcelain 
  or 
  white 
  earthenware 
  manufacture, 
  to 
  

   prevent 
  discoloration 
  of 
  the 
  ware. 
  Again, 
  the 
  combination 
  of 
  

   fluxes 
  in 
  large 
  amount 
  may 
  be 
  desirable 
  for 
  the 
  production 
  of 
  a 
  

   vitrified 
  body, 
  such 
  as 
  is 
  required 
  for 
  paving 
  brick 
  or 
  se^^er 
  pipe. 
  

  

  In 
  kaolins 
  the 
  amount 
  of 
  fluxes 
  may 
  be 
  as 
  high 
  as 
  7fo 
  provided 
  

   they 
  do 
  not 
  exert, 
  a 
  coloring 
  action. 
  Some 
  of 
  the 
  best 
  kaolins 
  known 
  

   contain 
  about 
  S6fo 
  of 
  feldspar, 
  which 
  means 
  about 
  5.6fo 
  of 
  potash. 
  

   In 
  fire 
  clay 
  4-5^ 
  is 
  the 
  permissible 
  limit, 
  depending 
  on 
  the 
  physical 
  

   properties 
  of 
  the 
  clay, 
  while 
  in 
  a 
  paving 
  brick 
  clay 
  the 
  total 
  of 
  

   fluxes 
  may 
  run 
  as 
  high 
  as 
  16^. 
  

  

  Alkalis 
  

   These 
  are 
  never 
  present 
  in 
  a 
  clay 
  in 
  the 
  form 
  in 
  which 
  they 
  are 
  

   determined 
  in 
  the 
  ordinary 
  quantitative 
  analysis, 
  but 
  generally 
  as 
  

   a 
  constituent 
  element 
  of 
  one 
  or 
  more 
  minerals. 
  Clay 
  may 
  contain 
  

   two 
  classes 
  of 
  alkalis, 
  fixed 
  and 
  volatile. 
  The 
  former 
  arc 
  soda, 
  

   potash 
  and 
  lithia, 
  the 
  latter 
  ammonia. 
  

  

  