﻿542 
  NEW 
  yore: 
  state 
  museum 
  

  

  that 
  it 
  is 
  the 
  rule, 
  and 
  that 
  high 
  tensile 
  strength 
  always 
  denotes 
  

   high 
  plasticity. 
  There 
  are 
  clays 
  running 
  low 
  in 
  their 
  tensile 
  

   strength 
  that 
  eixhibit 
  marked 
  plasticity, 
  as 
  for 
  example 
  some 
  of 
  the 
  

   JSTew 
  Jersey 
  clays, 
  or 
  some 
  English 
  ball-clays, 
  but 
  on 
  the 
  other 
  

   hand 
  it 
  can 
  be 
  said 
  that 
  probably 
  no 
  clay 
  of 
  low 
  plasticity 
  Las 
  

   high 
  tensile 
  strength. 
  

  

  A 
  means 
  of 
  measuring 
  the 
  plasticity 
  of 
  a 
  clay 
  and 
  expressing 
  it 
  

   numerically 
  for 
  purposes 
  of 
  comparison 
  has 
  been 
  the 
  one 
  aim 
  of 
  

   clay 
  technologists. 
  Several 
  methods 
  have 
  been 
  suggested, 
  none 
  

   meeting 
  with 
  universal, 
  and 
  few 
  with 
  even 
  partial 
  adoption. 
  One 
  

   of 
  the 
  more 
  important 
  is 
  testing 
  with 
  Yicat's 
  needle. 
  

  

  The 
  clay 
  is 
  reduced, 
  with 
  water 
  to 
  a 
  mass 
  of 
  the 
  proper 
  con- 
  

   sistency 
  for 
  ordinary 
  working. 
  It 
  is 
  then 
  forced 
  into 
  a 
  metal 
  

   ring, 
  and 
  the 
  resistance 
  which 
  it 
  offers 
  to 
  a 
  steel 
  wire 
  of 
  given 
  

   size 
  under 
  known 
  pressure 
  is 
  noted. 
  This 
  method 
  is 
  followed 
  in 
  

   cement 
  testing, 
  and 
  the 
  apparatus 
  is 
  known 
  as 
  Yicat's 
  needle. 
  It 
  

   gives 
  the 
  most 
  satisfaction 
  for 
  comparative 
  testing, 
  that 
  is 
  for 
  de- 
  

   termining 
  the 
  relative 
  plasticities 
  of 
  several 
  clays 
  examined 
  at 
  the 
  

   same 
  time. 
  

  

  A 
  second 
  method 
  is 
  to 
  mold 
  the 
  plastic 
  clay 
  in 
  a 
  briquet 
  

   mold 
  similar 
  to 
  that 
  used 
  in 
  testing 
  cement, 
  care 
  being 
  taken 
  that 
  

   the 
  clay 
  briquet 
  is 
  homogeneous 
  throughout 
  and 
  contains 
  no 
  

   flaws. 
  It 
  is 
  then 
  allowed 
  tO' 
  dry 
  thoroughly, 
  and 
  subsequently 
  

   pulled 
  apart 
  in 
  a 
  cement 
  testing 
  machine, 
  the 
  tensile 
  strength 
  being 
  

   expressed 
  in 
  pounds 
  per 
  square 
  inch. 
  As 
  the 
  clay 
  shrinks 
  in 
  dry- 
  

   ing, 
  it 
  is 
  necessary 
  to 
  measure 
  thei 
  crossHsection 
  of 
  the 
  briquet 
  be- 
  

   fore 
  breaking 
  it, 
  and 
  to 
  calculate 
  from 
  this 
  the 
  strength 
  of 
  a 
  

   briquet 
  whose 
  cross-section 
  is 
  one 
  square 
  inch. 
  

  

  Another 
  method 
  is 
  to 
  form 
  the 
  plastic 
  clay 
  into 
  a 
  <3ylinder, 
  

   which 
  is 
  placed 
  horizontally 
  in 
  a 
  semicircular 
  channel 
  of 
  the 
  same 
  

   diameter, 
  and 
  so 
  arranged 
  that 
  a 
  wire 
  can 
  be 
  laid 
  across 
  it 
  at 
  right 
  

   angles. 
  A 
  weight 
  is 
  attached 
  to- 
  the 
  wire, 
  and 
  the 
  time 
  which 
  ia 
  

   required 
  for 
  the 
  wire 
  to 
  cut 
  through 
  the 
  clay 
  observed.^ 
  

  

  « 
  

  

  ^ 
  C. 
  F. 
  Binus. 
  Ceramic 
  technology, 
  p. 
  86. 
  

  

  