﻿JFotes 
  on 
  the 
  Plug 
  Permeameter. 
  133 
  

  

  Recourse 
  was 
  therefore 
  had 
  to 
  the 
  more 
  simple 
  device 
  of 
  

   obtaining 
  some 
  specimens 
  of 
  cast 
  and 
  wrought 
  iron 
  and 
  

   steel, 
  in 
  the 
  form 
  of 
  rings 
  ; 
  testing 
  them 
  by 
  the 
  ordinary 
  

   ring 
  method, 
  and 
  afterwards 
  cutting 
  them 
  up 
  and 
  drilling, 
  

   for 
  tests 
  by 
  the 
  plug. 
  Rings 
  of 
  this 
  kind 
  were 
  made 
  for 
  us 
  

   by 
  Messrs. 
  Gr. 
  Wailes 
  of 
  Euston 
  Road, 
  and 
  were 
  of 
  ordinary 
  

   cast 
  iron 
  (O.C.I.), 
  special 
  cast 
  iron 
  (S.C.I.), 
  wrought 
  iron 
  

   (W.I.), 
  and 
  mild 
  steel 
  (M.S.). 
  Two 
  rings 
  of 
  each 
  material 
  

   were 
  tested, 
  and 
  each 
  ring 
  was 
  cut 
  into 
  four 
  quadrants. 
  

   Each 
  of 
  these 
  quadrants 
  was 
  drilled 
  in 
  both 
  ends, 
  so 
  that 
  

   eight 
  drillings 
  were 
  made 
  in 
  each 
  ring. 
  Readings 
  of 
  B 
  were 
  

   then 
  made 
  with 
  the 
  plug 
  method, 
  at 
  nominal 
  values 
  of 
  H 
  of 
  

   30 
  and 
  100 
  on 
  the 
  eight 
  drillings, 
  and 
  the 
  drilling 
  selected 
  

   for 
  final 
  test, 
  the 
  readings 
  on 
  which 
  corresponded 
  to 
  the 
  mean 
  

   of 
  the 
  eight. 
  It 
  may 
  be 
  mentioned 
  that 
  the 
  whole 
  of 
  the 
  

   61 
  drillings 
  on 
  the 
  eight 
  rings 
  were 
  made 
  with 
  the 
  same 
  

   drill, 
  which 
  was 
  none 
  the 
  worse 
  after. 
  None 
  of 
  the 
  drillings 
  

  

  Fte. 
  1. 
  

  

  gave 
  a 
  bad 
  fit 
  with 
  the 
  plug. 
  Fig. 
  1 
  shows 
  the 
  form 
  and 
  

   mode 
  of 
  cutting 
  and 
  drilling 
  the 
  ring, 
  which 
  was 
  5 
  in. 
  ex- 
  

   ternal 
  diameter 
  and 
  1 
  in. 
  square 
  in 
  section 
  ; 
  while 
  Table 
  I. 
  

   shows 
  an 
  example 
  of 
  the 
  readings 
  on 
  the 
  various 
  drillings 
  of 
  

   one 
  ring, 
  and 
  the 
  amount 
  of 
  variation 
  usually 
  found. 
  It 
  

   should 
  be 
  specially 
  noted 
  that 
  these 
  variations 
  are 
  not 
  appa- 
  

   rently 
  due 
  to 
  variation 
  in 
  the 
  fit 
  of 
  the 
  plug, 
  but 
  rather 
  to 
  

   actual 
  differences 
  in 
  the 
  magnetic 
  quality 
  of 
  the 
  iron. 
  

  

  