﻿552 
  Is'EW 
  YOEK 
  STATE 
  MUSEUM 
  

  

  clays 
  tliey 
  may 
  not 
  be 
  over 
  50° 
  F. 
  apart, 
  while 
  in 
  refractory 
  clays 
  

   they 
  are 
  separated 
  sometimes 
  by 
  an 
  interval 
  of 
  700° 
  or 
  

   800° 
  F. 
  The 
  glass 
  pot 
  clays 
  approach 
  the. 
  latter 
  condition. 
  The 
  

   majority 
  of 
  clays 
  show 
  a 
  difference 
  of 
  200°-400° 
  between 
  the 
  

   points 
  of 
  incipient 
  fusion 
  and 
  viscosity. 
  

  

  The 
  practical 
  bearing 
  of 
  this 
  will 
  be 
  easily 
  seen, 
  when 
  one 
  re- 
  

   members 
  that 
  in 
  the 
  manufacture 
  of 
  many 
  kinds 
  of 
  clay 
  products, 
  

   the 
  body 
  has 
  to 
  be 
  vitrified. 
  Consequently 
  the 
  greater 
  the 
  differ- 
  

   ence 
  between 
  the 
  temperature 
  of 
  vitrification 
  and 
  that 
  of 
  viscosity, 
  

   the 
  easier 
  will 
  it 
  be 
  to 
  bring 
  a 
  kiln 
  of 
  ware 
  up 
  to 
  the 
  one 
  without 
  

   ovei^tepping 
  it 
  and 
  reaching 
  thje 
  other, 
  for 
  kilns 
  can 
  not 
  be 
  regu- 
  

   lated 
  within 
  a 
  range 
  of 
  a 
  few 
  degrees 
  of 
  temperature. 
  

  

  In 
  many 
  clays 
  the 
  point 
  of 
  vitrification 
  is 
  midway 
  between 
  in- 
  

   cipient 
  fusion 
  and 
  viscosity, 
  but 
  in 
  others 
  it 
  is 
  not. 
  

  

  Temperature 
  of 
  fusion. 
  The 
  fusibility 
  of 
  a 
  clay 
  depends 
  on: 
  

  

  1 
  The 
  amount 
  of 
  fluxes 
  

  

  2 
  The 
  size 
  of 
  the 
  grain 
  of 
  the 
  refractory 
  and 
  nonrefractory 
  con- 
  

   stituents 
  

  

  3 
  The 
  condition 
  of 
  the 
  fire, 
  whether 
  oxidizing 
  or 
  reducing 
  

  

  All 
  the 
  fluxing 
  impurities 
  do 
  not 
  act 
  with 
  the 
  same 
  intensity. 
  

   Fine-grained 
  clays 
  fuse 
  at 
  lower 
  temperatures 
  than 
  coarse-gTained 
  

   ones, 
  other 
  things 
  being 
  equal."" 
  

  

  In 
  order 
  to 
  express 
  the 
  relative 
  fusibility 
  of 
  clays 
  numerically, 
  

   Bischof-^, 
  on 
  the 
  assumption 
  that 
  the 
  refractoriness 
  of 
  a 
  clay 
  is 
  

   directly 
  as 
  the 
  square 
  of 
  the 
  alumina 
  and 
  inversely 
  as 
  the 
  silica 
  and 
  

   fluxes, 
  deduced 
  the 
  following 
  formula, 
  in 
  which 
  F. 
  Q. 
  stands 
  for 
  

   the 
  ^' 
  refractory 
  quotient 
  ''. 
  

   F 
  Q 
  = 
  i^i^^ 
  

  

  SiO-^xRO 
  

   This 
  has 
  been 
  found 
  incorrect 
  when 
  there 
  is 
  a 
  variation 
  in 
  the 
  

   fineness 
  and 
  density 
  of 
  the 
  clay, 
  and 
  in 
  order 
  to 
  recogTiize 
  the 
  effect 
  

   of 
  these 
  two 
  features, 
  Wheeler^ 
  has 
  suggested 
  the 
  formula 
  : 
  F. 
  F.= 
  

  

  T. 
  , 
  ,„ 
  I 
  ^ 
  , 
  in 
  which 
  F. 
  F. 
  is 
  called 
  the 
  fusibility 
  factor. 
  

  

  '^ 
  Die 
  feuerfesten 
  thone, 
  p. 
  71. 
  1876. 
  

   ^Eng. 
  and 
  min. 
  jour. 
  10 
  Mar. 
  1894. 
  

  

  